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CCNA Route Summarization Questions

75 of 76 questions · Page 1/2 · Route Summarization topic · Answers revealed

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1
MCQmedium

Consider the following partial EIGRP configuration on router R1: router eigrp 100 network 10.0.0.0 network 192.168.1.0 summary-address 10.0.0.0 255.255.255.0 5 What is the effect of the 'summary-address 10.0.0.0 255.255.255.0 5' command?

A.It creates a summary route 10.0.0.0/24 with an administrative distance of 5, advertised out all EIGRP-enabled interfaces.
B.It creates a summary route 10.0.0.0/24 and sets the metric to 5.
C.It creates a summary route 10.0.0.0/24 and suppresses more specific routes with a metric of 5.
D.It creates a summary route 10.0.0.0/24 with a tag of 5.
AnswerA

Correct. The summary-address command creates a summary route and the optional distance value sets the administrative distance for that summary.

Why this answer

The 'summary-address' command in EIGRP creates a summary route and advertises it out all interfaces enabled for EIGRP. The administrative distance value (5) is optional and sets the distance for the summary route.

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2
MCQmedium

A network engineer runs the following command on Router R1: R1# show ip ospf database summary 172.16.0.0 OSPF Router with ID (1.1.1.1) (Process ID 1) Summary Net Link States (Area 0) LS age: 100 Options: (No TOS-capability, DC) LS Type: Summary Links(Network) Link State ID: 172.16.0.0 (Summary Network Number) Advertising Router: 2.2.2.2 LS Seq Number: 80000001 Checksum: 0x1234 Length: 28 Network Mask: /20 TOS: 0 Metric: 10 Based on this output, what does this LSA represent?

A.It is a router LSA from R1.
B.It is a summary route for 172.16.0.0/20 advertised by ABR 2.2.2.2.
C.It is an external route from ASBR.
D.It is a network LSA for the 172.16.0.0 network.
AnswerB

This Type 3 LSA advertises a summary route for 172.16.0.0/20 from ABR 2.2.2.2.

Why this answer

This is a Type 3 Summary LSA, which is used to advertise inter-area routes. The Advertising Router is 2.2.2.2, an ABR.

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3
MCQhard

A large enterprise network is experiencing intermittent reachability to a specific /24 subnet (192.168.10.0/24) from remote sites. Router R1 has the following relevant configuration: interface GigabitEthernet0/0 ip address 10.0.1.1 255.255.255.0 ! router eigrp 100 network 10.0.0.0 network 192.168.0.0 ! interface GigabitEthernet0/1 ip address 192.168.1.1 255.255.255.0 ip summary-address eigrp 100 192.168.0.0 255.255.252.0 ! Router R2 shows: R2# show ip route 192.168.10.0 Routing entry for 192.168.0.0/22, supernet Known via "eigrp 100", distance 90, metric 30720, type internal Last update from 10.0.1.1 on GigabitEthernet0/0, 00:00:15 ago * 10.0.1.1, via GigabitEthernet0/0, 00:00:15 ago What is the root cause?

A.The summary route 192.168.0.0/22 does not include 192.168.10.0/24, so the specific route is not advertised and is missing from R2's routing table.
B.EIGRP has a metric mismatch between the summary and the specific route, causing the specific route to be suppressed.
C.The network command for 192.168.0.0 is missing, causing EIGRP to not advertise any 192.168.x.x routes.
D.R2 has a static route for 192.168.10.0/24 that is overriding the EIGRP route.
AnswerA

The summary covers only 192.168.0.0-192.168.3.255, excluding 192.168.10.0/24.

Why this answer

The summary route 192.168.0.0/22 is being advertised by R1, but it blocks the more specific /24 route 192.168.10.0/24 if that subnet is not within the summary range (192.168.0.0/22 covers 192.168.0.0 to 192.168.3.255). Since 192.168.10.0/24 is outside this range, it is not summarized and is not advertised separately, causing reachability failure. The correct fix is to adjust the summary prefix to include the missing subnet, or to not summarize.

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4
MCQmedium

Review the following OSPF configuration on router R4: router ospf 1 network 10.0.0.0 0.255.255.255 area 0 area 1 range 10.0.0.0 255.255.255.0 What is missing or incorrect in this configuration for proper route summarization?

A.The router must have interfaces in area 1 for the summarization to take effect.
B.The mask should be 0.0.0.255 instead of 255.255.255.0.
C.The command should be 'summary-address' instead of 'area range'.
D.The network statement should include area 1.
AnswerA

Correct. The area range command only works if the router is an ABR, meaning it has interfaces in multiple areas.

Why this answer

The area range command is used on an ABR to summarize routes from one area into another. Here, area 1 is specified, but router R4 only has network statements in area 0, so it is not an ABR for area 1. The command will have no effect.

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5
MCQmedium

A network engineer is troubleshooting a route summarization issue in a network using RIP. Router R1 is configured with the 'ip summary-address rip 192.168.0.0 255.255.252.0' command on its serial interface. After the configuration, R2, which is connected via that interface, can no longer reach the 192.168.1.0/24 subnet, although other subnets within the summary are reachable. What is the most likely cause?

A.The 192.168.1.0/24 subnet is not directly connected to R1, so it cannot be summarized.
B.The summary route 192.168.0.0/22 is being advertised with a higher metric than the specific routes, causing R2 to prefer a different path.
C.The summary address command was applied on the wrong interface, causing the summary to be sent out all interfaces, including the one facing the 192.168.1.0/24 subnet's origin.
D.The 192.168.1.0/24 subnet is not included in the summary range because the summary mask is /22, but the subnet's network address is 192.168.1.0, which is within the range, but the RIP process may have a split-horizon issue preventing the route from being advertised.
AnswerD

Correct. In RIP, split horizon prevents a route from being advertised out the interface it was learned on. If the 192.168.1.0/24 subnet was learned on the same interface where the summary is applied, it will not be advertised, causing loss of connectivity.

Why this answer

In RIP, the summary-address command suppresses the advertisement of more specific routes. However, if the summary route is not installed in the routing table (e.g., due to a metric issue), the specific routes may still be suppressed, causing loss of connectivity.

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6
MCQmedium

In EIGRP, what is the default behavior of auto-summary in IOS-XE versions 15.0 and later?

A.Auto-summary is enabled by default.
B.Auto-summary is disabled by default.
C.Auto-summary is enabled only for EIGRP named mode.
D.Auto-summary is disabled only for EIGRP classic mode.
AnswerB

Cisco changed the default to disabled starting with IOS-XE 15.0.

Why this answer

Cisco IOS-XE 15.0 and later have auto-summary disabled by default for EIGRP, unlike older IOS versions where it was enabled by default.

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7
MCQhard

An engineer configures OSPF on two routers connected via a point-to-point link. The routers are stuck in EXSTART state. 'show ip ospf neighbor' shows neighbor state EXSTART/EXCHANGE. Which is the most likely explanation?

A.The OSPF network type is mismatched (point-to-point vs broadcast).
B.The MTU on the interfaces is mismatched.
C.The OSPF router IDs are identical.
D.The hello/dead intervals are mismatched.
AnswerB

An MTU mismatch prevents DBD packets from being exchanged, causing the adjacency to remain in EXSTART.

Why this answer

In OSPF, the EXSTART state involves negotiating the master/slave relationship and the Database Description (DBD) packet size. If the MTU on the interfaces differs, the larger DBD packet from the router with the larger MTU will be dropped by the router with the smaller MTU, causing the adjacency to remain stuck in EXSTART. This is a common edge case that is often overlooked.

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8
MCQhard

MPLS LDP neighbor mismatch is causing label distribution failures for summary routes. Router R1 and R2 are LDP peers. R1 has: mpls ip ! interface GigabitEthernet0/0 ip address 10.0.0.1 255.255.255.0 mpls ip ! router ospf 1 network 10.0.0.0 0.0.0.255 area 0 area 0 range 10.0.0.0 255.255.252.0 ! R2 shows: R2# show mpls ldp neighbor Peer LDP Ident: 10.0.0.2:0, Transport address: 10.0.0.2 TCP connection: 10.0.0.2.646 - 10.0.0.1.646 State: Oper, Msgs sent/rcvd: 10/10 R2# show mpls forwarding-table 10.0.0.0/22 Local tag outgoing tag prefix tag(s) next-hop 16 Untagged 10.0.0.0/22 0 10.0.0.1 But R2 cannot forward traffic for 10.0.1.0/24. What is the root cause?

A.The OSPF summary suppresses the /24 routes, so LDP does not assign labels to them, causing forwarding failures.
B.LDP is not enabled on the interface, so no labels are exchanged.
C.The OSPF area range command is not supported with MPLS.
D.R2 has a static route for 10.0.1.0/24 that overrides LDP.
AnswerA

LDP only labels routes present in the routing table; the /24 routes are missing.

Why this answer

The OSPF area range command creates a summary route 10.0.0.0/22 in the routing table, but LDP assigns labels only to routes that are in the routing table. The more specific /24 routes are suppressed by the summary, so LDP does not have labels for them. When R2 receives a packet for 10.0.1.0/24, it looks up the route, finds the summary, and forwards it to R1 with a label, but R1 may not have a label for the specific /24, causing a label mismatch or blackholing.

The fix is to not summarize or to use label binding for more specific prefixes.

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9
MCQhard

An engineer configures route summarization in OSPF using the 'area range' command. After configuration, some routes are missing from the routing table of other routers. Which is the most likely explanation?

A.The 'area range' command is configured with the 'not-advertise' keyword, suppressing the summary.
B.The summary route is being filtered by a distribute-list on the receiving router.
C.The component routes are not present in the OSPF database.
D.The summary route is being advertised with a metric that is too high.
AnswerA

The 'not-advertise' keyword explicitly prevents the summary route from being advertised, which would cause the routes to be missing.

Why this answer

The 'area range' command in OSPF creates a summary route that is advertised as a Type 3 LSA. However, if the 'not-advertise' keyword is used, the summary route is suppressed. Additionally, if the summary route is more specific than the component routes, it may be rejected by the receiving router due to OSPF's route selection rules.

Another edge case is that the summary route may be created but the component routes are still advertised individually if the 'advertise' keyword is not explicitly used (default is advertise).

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10
MCQhard

A network engineer is troubleshooting an OSPF network where routers R1, R2, and R3 are in area 0. R1 has a summary route 192.168.0.0/22 configured on its interface to R2, summarizing four /24 subnets (192.168.0.0/24 through 192.168.3.0/24). After the configuration, R3 loses connectivity to the 192.168.0.0/24 subnet, although other subnets are reachable. What is the most likely cause?

A.The summary route 192.168.0.0/22 is being advertised with a metric of 0, causing R3 to prefer a less specific route from another source.
B.The summary-address command was applied on R1 as an ABR, but R1 is not an ABR because it is in area 0 only; the command is ignored.
C.The 192.168.0.0/24 subnet is not included in the summary because the summary mask is /22, but the subnet mask of 192.168.0.0/24 is not contiguous with the others due to a configuration error.
D.The summary-address command on R1 is configured with the 'not-advertise' keyword, suppressing the summary but not the specific routes, causing a routing black hole for the 192.168.0.0/24 subnet.
AnswerD

Correct. The 'not-advertise' keyword in OSPF summary-address prevents the summary from being advertised, but the specific routes may still be suppressed if the command is misapplied, leading to loss of connectivity to the specific subnet.

Why this answer

The issue is that the summary route may be suppressing the more specific routes, but the summary itself might not be installed due to a mismatch or missing component. In OSPF, the summary-address command on an ASBR or ABR can cause issues if the metric or type is misconfigured.

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11
MCQmedium

A network engineer is troubleshooting a BGP route summarization issue. Router R1 is configured with the 'aggregate-address 192.168.0.0 255.255.252.0' command without any keywords. The engineer notices that the ISP neighbor is receiving both the aggregate route and the more specific routes (192.168.0.0/24, 192.168.1.0/24, etc.), causing the ISP to prefer the specific routes. What should the engineer do to ensure the aggregate route is preferred?

A.Add the 'summary-only' keyword to the aggregate-address command.
B.Remove the network statements for the specific subnets from the BGP process.
C.Configure a route-map to set a higher local preference on the aggregate route.
D.Use the 'aggregate-address' command with the 'as-set' keyword.
AnswerA

Correct. The summary-only keyword suppresses the advertisement of more specific routes, leaving only the aggregate route.

Why this answer

By default, BGP prefers more specific routes over less specific ones. To make the aggregate route preferred, the engineer can use the 'summary-only' keyword to suppress specific routes, or use attributes like AS_PATH to make the aggregate more attractive.

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12
MCQhard

A network engineer runs the following command on Router R1: R1# show ip eigrp topology summary IP-EIGRP Topology Table for AS(100)/ID(1.1.1.1) Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply, r - reply Status, s - sia Status P 10.0.0.0/8, 1 successors, FD is 2812416, serno 10 via Summary (2812416/0), Null0 P 10.0.0.0/24, 1 successors, FD is 2172416, serno 5 via 192.168.1.2 (2172416/2812416), GigabitEthernet0/0 P 10.0.1.0/24, 1 successors, FD is 2172416, serno 6 via 192.168.1.2 (2172416/2812416), GigabitEthernet0/0 Based on this output, what is the purpose of the route 10.0.0.0/8 via Null0?

A.It is a default route for unknown destinations.
B.It is a discard route to prevent routing loops.
C.It is a route learned from a neighbor.
D.It is a connected route.
AnswerB

The Null0 interface indicates this is a discard route, commonly used with summarization to avoid loops.

Why this answer

The route 10.0.0.0/8 via Null0 is a summary route created by the 'summary-address' command in EIGRP, used to prevent routing loops by discarding packets that do not match more specific routes.

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13
MCQhard

A network engineer is troubleshooting a route summarization issue in a network using OSPFv3. Router R1 is configured with the 'ipv6 summary-address 2001:db8:0:1::/64' command under the OSPFv3 process. After the configuration, routers in the same area lose connectivity to the 2001:db8:0:1:1::/80 subnet, which is one of the component routes. What is the most likely cause?

A.The summary-address command in OSPFv3 requires a prefix-length, not a mask; the engineer used a /64 prefix, which is too specific to summarize the /80 subnet.
B.The OSPFv3 process is not enabled on the interface facing the 2001:db8:0:1:1::/80 subnet.
C.The summary-address command should be applied on the interface, not under the OSPFv3 process.
D.The 2001:db8:0:1:1::/80 subnet is not in the OSPFv3 database because it is redistributed from another protocol.
AnswerA

Correct. The summary-address command in OSPFv3 uses a prefix length. A /64 summary will not include a /80 subnet because the /80 is more specific and falls outside the summary range.

Why this answer

In OSPFv3, the summary-address command works similarly to OSPFv2. The issue may be that the summary route is not being generated because the component routes are not in the OSPFv3 database, or the summary mask is too specific.

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14
Drag & Drophard

Drag and drop the steps to troubleshoot route summarization adjacency or connectivity failures into the correct order, from first to last.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps
Order
1Step 1
2Step 2
3Step 3
4Step 4
5Step 5

Why this order

Start by verifying that the summarization router has a route to the null0 interface to prevent loops. Then, confirm that the summary route is being advertised to neighbors using show ip route. Next, check that the neighbor router receives the summary in its routing table.

After that, examine the neighbor's routing table for the specific summarized prefix. Finally, test end-to-end connectivity using ping or traceroute to ensure the summary works.

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15
MCQhard

A network engineer is troubleshooting an OSPF network where an ABR (R1) is configured with the 'area 1 range 10.0.0.0 255.255.0.0' command to summarize routes from area 1 into area 0. After the configuration, routers in area 0 lose connectivity to the 10.0.1.0/24 subnet, although the summary route 10.0.0.0/16 is present in their routing tables. What is the most likely cause?

A.The summary route 10.0.0.0/16 is being advertised with a metric of 0, causing routers to prefer a default route instead.
B.The ABR is not generating the summary route because the component routes are not all in the same area.
C.The 10.0.1.0/24 subnet is not included in the summary range because the range command uses a network mask that does not match the subnet's network address.
D.The summary route is installed, but the next-hop IP address for the summary route is not reachable from routers in area 0, causing traffic to be dropped.
AnswerD

Correct. In OSPF, the summary route's next hop is set to the ABR's interface IP. If that interface is down or the path is not reachable, traffic to the summary may fail, and since specific routes are suppressed, connectivity to the subnet is lost.

Why this answer

The issue is that the summary route may be installed, but the more specific routes are suppressed. If the summary route points to a next hop that is not reachable or has a higher metric, traffic may be black-holed.

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16
Multi-Selecthard

An engineer is troubleshooting an OSPF network where route summarization is configured on an ABR. Which TWO statements correctly describe the behavior of OSPF inter-area route summarization using the 'area range' command? (Choose TWO.)

Select 2 answers
A.The 'area range' command creates a single Type 3 LSA for the summary prefix and suppresses the advertisement of individual Type 3 LSAs for the component networks.
B.The cost of the summary LSA is set to the lowest cost among the component routes within the range.
C.The 'area range' command also summarizes external routes redistributed into OSPF from other protocols.
D.The summary route is advertised with a metric type of E1 or E2, depending on the original external metric type.
E.The 'area range' command can be configured only on ABRs and not on ASBRs.
AnswersA, E

Correct. The ABR generates one Type 3 LSA for the range and does not advertise the individual Type 3 LSAs for the more specific routes.

Why this answer

The 'area range' command on an ABR summarizes routes from one area into another. It creates a single Type 3 LSA for the summary prefix, suppresses the individual Type 3 LSAs for the component networks, and does not affect Type 1 or Type 2 LSAs within the area. The summary LSA is advertised with a cost equal to the highest cost among the component routes, not the lowest.

The command does not automatically summarize redistributed routes; that requires the 'summary-address' command under the OSPF process.

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17
MCQmedium

Consider this EIGRP configuration on router R5: interface GigabitEthernet0/0 ip summary-address eigrp 100 10.10.0.0 255.255.0.0 5 router eigrp 100 network 10.0.0.0 What is the effect of the 'ip summary-address eigrp' command on interface GigabitEthernet0/0?

A.It creates a summary route 10.10.0.0/16 with administrative distance 5, advertised only out GigabitEthernet0/0.
B.It creates a summary route 10.10.0.0/16 with metric 5, advertised out all interfaces.
C.It creates a summary route 10.10.0.0/16 and suppresses all more specific routes globally.
D.It creates a summary route 10.10.0.0/16 and redistributes it into other routing protocols.
AnswerA

Correct. The command is interface-specific and the distance value is optional.

Why this answer

The interface-level 'ip summary-address eigrp' command creates a summary route that is advertised out that specific interface. The optional administrative distance (5) sets the distance for the summary route.

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18
MCQhard

A network engineer runs the following command on Router R1: R1# show ip route 10.0.0.0 255.255.252.0 longer-prefixes Routing entry for 10.0.0.0/22 Known via "eigrp 100", distance 90, metric 2172416, type internal Last update from 192.168.1.2 on GigabitEthernet0/0, 00:00:10 ago Routing Descriptor Blocks: * 192.168.1.2, from 192.168.1.2, 00:00:10 ago, via GigabitEthernet0/0 Route metric is 2172416, traffic share count is 1 Routing entry for 10.0.1.0/24 Known via "eigrp 100", distance 90, metric 2812416, type internal Last update from 192.168.1.2 on GigabitEthernet0/0, 00:00:10 ago Routing Descriptor Blocks: * 192.168.1.2, from 192.168.1.2, 00:00:10 ago, via GigabitEthernet0/0 Route metric is 2812416, traffic share count is 1 Based on this output, what is the effect of the summary route 10.0.0.0/22?

A.The summary route is working correctly and suppressing all specifics.
B.The summary route is not suppressing the more specific route 10.0.1.0/24.
C.The summary route has a better metric than the specific route.
D.The summary route is not installed in the routing table.
AnswerB

Both the summary and a more specific route are in the table, indicating the summary is not suppressing specifics.

Why this answer

The presence of both the summary route (10.0.0.0/22) and a more specific route (10.0.1.0/24) in the routing table indicates that the summary route is not suppressing the more specific routes, possibly due to a configuration issue or because the summary is not configured as a discard route.

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19
MCQmedium

Examine this BGP configuration on router R3: router bgp 65001 neighbor 10.1.1.1 remote-as 65002 address-family ipv4 network 192.168.0.0 mask 255.255.252.0 aggregate-address 192.168.0.0 255.255.252.0 summary-only What is the effect of the 'aggregate-address' command with the 'summary-only' keyword?

A.It advertises the aggregate 192.168.0.0/22 and suppresses all more specific routes from being advertised to neighbor 10.1.1.1.
B.It advertises both the aggregate and all more specific routes.
C.It creates a static route for the aggregate.
D.It removes all more specific routes from the BGP table.
AnswerA

Correct. The summary-only keyword ensures only the aggregate is advertised, not the specifics.

Why this answer

The aggregate-address command creates an aggregate route in BGP. The summary-only keyword suppresses more specific routes from being advertised.

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20
MCQmedium

A network engineer runs the following command on Router R1: R1# show ip bgp 192.168.0.0 255.255.252.0 BGP routing table entry for 192.168.0.0/22, version 5 Paths: (1 available, best #1, table default) Advertised to update-groups: 1 Refresh Epoch 1 65001 10.1.1.1 from 10.1.1.1 (10.1.1.1) Origin IGP, metric 0, localpref 100, valid, external, best Community: 65001:100 rx pathid: 0, tx pathid: 0x0 Aggregator: 65001, 10.1.1.1 Based on this output, what is true about this route?

A.The route is a summary route aggregated by 10.1.1.1.
B.The route is a learned route from AS 65002.
C.The route is a default route.
D.The route is suppressed.
AnswerA

The Aggregator field shows 65001, 10.1.1.1, indicating this route is an aggregate.

Why this answer

The presence of 'Aggregator' indicates route summarization (aggregation) was performed by the router with IP 10.1.1.1 in AS 65001.

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21
MCQmedium

Which BGP attribute is used as the first tie-breaker when selecting the best path for route summarization?

A.Local preference
B.Weight
C.AS path length
D.MED
AnswerB

Weight is Cisco-specific and is checked first.

Why this answer

The highest weight (locally configured) is the first tie-breaker in BGP path selection, before local preference.

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22
Multi-Selecthard

Which TWO statements correctly describe the behavior of route summarization in RIP? (Choose TWO.)

Select 2 answers
A.RIPv2 automatically summarizes routes to their classful boundary by default, and this behavior can be disabled with the 'no auto-summary' command.
B.Manual route summarization in RIP is configured using the 'network' command under the RIP process.
C.When manual summarization is configured, RIP automatically installs a discard route for the summary prefix to prevent routing loops.
D.The summary route in RIP is advertised with a metric equal to the lowest hop count among the component routes.
E.RIP supports both automatic and manual summarization only for classful networks.
AnswersA, C

Correct. RIPv2 has auto-summary enabled by default, which causes classful summarization. It can be disabled to allow VLSM and CIDR prefixes.

Why this answer

RIP version 2 supports automatic summarization by default (enabled with 'auto-summary'), which summarizes networks at classful boundaries. This can be disabled with 'no auto-summary'. Manual summarization is configured using 'ip summary-address rip' under an interface.

The summary route is advertised with the metric of the best component route, and a discard route is automatically installed to prevent loops. RIP does not support VLSM summarization by default unless auto-summary is disabled.

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23
MCQmedium

Which OSPF LSA type is used to advertise a summary route for a network outside the area but within the same OSPF domain?

A.Type 1
B.Type 2
C.Type 3
D.Type 5
AnswerC

Type 3 LSAs are Summary LSAs, used for inter-area routes.

Why this answer

Type 3 LSAs (Summary LSAs) are generated by Area Border Routers (ABRs) to advertise inter-area routes.

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24
MCQhard

BGP route summarization is causing unexpected path selection for prefix 172.16.0.0/16. Router R1 (AS 65001) has: router bgp 65001 neighbor 10.0.0.2 remote-as 65002 network 172.16.0.0 mask 255.255.0.0 aggregate-address 172.16.0.0 255.255.0.0 summary-only ! Router R2 (AS 65002) receives the aggregate and shows: R2# show ip bgp 172.16.0.0/16 BGP routing table entry for 172.16.0.0/16, version 2 Paths: (1 available, best #1) 65001, (aggregated by 65001 10.0.0.1) 10.0.0.1 from 10.0.0.1 (10.0.0.1) Origin IGP, localpref 100, valid, external, best However, R2 has a more specific route for 172.16.1.0/24 via another path with higher local preference. What is the root cause?

A.The summary-only keyword suppresses all more specific routes, so the /24 route is not advertised to R2, forcing R2 to use the aggregate.
B.The aggregate-address command is missing the as-set keyword, causing the aggregate to have incorrect path attributes.
C.R2's local preference for the /24 is lower than the aggregate, so it prefers the aggregate.
D.The network command for 172.16.0.0/16 is missing, so the aggregate is not generated.
AnswerA

summary-only prevents any more specific routes from being advertised.

Why this answer

The aggregate-address with summary-only suppresses all more specific routes, so R2 does not see the /24 route. Even if R2 had a better path for the /24, it is not advertised due to summary-only. This can cause suboptimal routing or blackholing if the aggregate points to a less preferred path.

The fix is to remove summary-only or use suppress-map to selectively suppress.

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25
MCQhard

Which OSPF network type defaults to a 30-second hello interval and requires a DR/BDR election?

A.Broadcast
B.Point-to-point
C.Non-broadcast (NBMA)
D.Point-to-multipoint
AnswerC

NBMA uses 30-second hello interval and elects DR/BDR.

Why this answer

Non-broadcast (NBMA) network type uses a 30-second hello interval and elects a DR/BDR, as per RFC 2328.

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26
Multi-Selecthard

Which TWO statements correctly describe the behavior of BGP route summarization using the 'aggregate-address' command? (Choose TWO.)

Select 2 answers
A.By default, the aggregate route is advertised with the ATOMIC_AGGREGATE attribute set.
B.The 'aggregate-address' command automatically suppresses the advertisement of all more specific routes.
C.The aggregate route inherits the AS_PATH of the longest matching more specific route.
D.The 'aggregate-address' command can be used to summarize both IPv4 and IPv6 prefixes in the same configuration.
E.The aggregate route is installed in the BGP table only if at least one more specific route exists in the BGP table.
AnswersA, E

Correct. When an aggregate is created, BGP sets the ATOMIC_AGGREGATE attribute to indicate that the path information might be incomplete.

Why this answer

The BGP 'aggregate-address' command creates a summary route in the BGP table. By default, the summary is advertised with the ATOMIC_AGGREGATE attribute and the aggregator router ID, but the more specific routes are still advertised unless the 'summary-only' keyword is used. The summary inherits the AS_PATH from the component routes, but the 'as-set' keyword is required to include the AS_PATH information in the aggregate.

The summary does not automatically suppress the component routes.

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27
Multi-Selecthard

Which THREE symptoms indicate that route summarization may be causing routing issues in a network? (Choose THREE.)

Select 3 answers
A.Suboptimal routing paths are observed for certain destinations.
B.Traffic to some subnets is dropped (black hole) even though the summary route exists.
C.Routing loops occur due to less specific summary routes pointing to routers that lack the specific subnet.
D.High CPU utilization on routers due to frequent SPF calculations.
E.Duplicate IP addresses are detected in the network.
AnswersA, B, C

Summarization can cause routers to choose a less specific route, leading to suboptimal paths.

Why this answer

Route summarization can cause suboptimal routing because the summary route may point to a less specific path. It can also cause black holes if the summary route is advertised but the specific subnets are not reachable. Additionally, summarization can hide more specific routes, leading to routing loops if the summary route is less specific and points to a router that does not have the specific subnet.

High CPU usage is not a direct symptom of summarization issues, and duplicate IP addresses are unrelated.

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28
MCQhard

An engineer configures IPsec between two routers. The tunnel does not come up. 'show crypto isakmp sa' shows MM_NO_STATE. Which is the most likely explanation?

A.The IKE mode is mismatched: the initiator is using aggressive mode, but the responder expects main mode.
B.The pre-shared key is mismatched.
C.The transform-set is mismatched.
D.The access-list for interesting traffic is misconfigured.
AnswerA

Aggressive mode and main mode are incompatible. If one side uses aggressive mode and the other uses main mode, the IKE exchange will fail, resulting in MM_NO_STATE.

Why this answer

MM_NO_STATE indicates that IKE Phase 1 has not started. In aggressive mode, the initiator sends all IKE parameters in the first packet, and if the responder does not have a matching policy, the exchange fails. However, a common edge case is that the responder is configured for main mode while the initiator is configured for aggressive mode, causing the exchange to fail before any state is established.

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29
Multi-Selecthard

Which TWO statements correctly describe the behavior of EIGRP route summarization when using the 'summary-address' command under an interface? (Choose TWO.)

Select 2 answers
A.A summary route is advertised with the metric equal to the best metric among the component routes.
B.The summary route is automatically assigned an administrative distance of 90 by default.
C.A local discard route (null0) is automatically installed for the summary prefix to prevent routing loops.
D.The 'summary-address' command also summarizes connected routes that fall within the summary range.
E.More specific routes are still advertised out the same interface even after the summary is configured.
AnswersA, C

Correct. EIGRP uses the best (lowest) metric from the component routes for the summary route advertisement.

Why this answer

EIGRP route summarization using the interface-level 'summary-address' command creates a local discard route to prevent routing loops, suppresses more specific routes from being advertised out that interface, and does not automatically summarize connected routes unless they are redistributed. The summary route is advertised with the metric of the best component route, and the administrative distance of the summary is set to 5 by default, not 90.

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30
MCQmedium

A network engineer runs the following command to troubleshoot a Route Summarization issue: R1# show ip access-lists CoPP-ACL extended IP access list CoPP-ACL 10 permit eigrp any any (100 matches) 20 permit ospf any any (50 matches) 30 permit bgp any any (200 matches) 40 deny ip any any (0 matches) What does this output indicate?

A.CoPP is permitting routing protocol traffic, including EIGRP, OSPF, and BGP, which are used for route summarization. No drops indicate CoPP is not blocking summarization.
B.CoPP is dropping all routing protocol traffic, preventing route summarization.
C.CoPP is only allowing BGP traffic, blocking EIGRP and OSPF summarization.
D.CoPP is not configured because the access list is empty.
AnswerA

The permit statements with matches show that routing protocol traffic is allowed, and no drops mean CoPP is not interfering.

Why this answer

This output shows an access list used for Control Plane Policing (CoPP). The match counts indicate that EIGRP, OSPF, and BGP traffic are being permitted. The absence of matches on the deny statement suggests that no traffic is being dropped, which could indicate that CoPP is not affecting route summarization traffic.

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31
MCQhard

OSPF network type mismatch on a multi-access link is causing route summarization issues. Router R1 and R2 are connected via Ethernet, but R1 has: interface GigabitEthernet0/0 ip address 10.0.0.1 255.255.255.0 ip ospf network point-to-point ip ospf 1 area 0 ! Router R2 has default OSPF network type (broadcast). R1 is configured with: router ospf 1 area 0 range 10.0.0.0 255.255.255.0 ! R2 shows: R2# show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.0.0.1 0 FULL/ - 00:00:30 10.0.0.1 GigabitEthernet0/0 But R2 does not have the summary route in its routing table. What is the root cause?

A.R1 is not an ABR (only area 0), so the area range command does not generate a summary route.
B.The network type mismatch causes OSPF to not exchange LSAs correctly, preventing the summary.
C.The summary route is suppressed because the interface is point-to-point.
D.R2 has a static route that overrides the summary.
AnswerA

Area range only works on ABRs that connect multiple areas.

Why this answer

The network type mismatch (point-to-point on R1, broadcast on R2) prevents proper adjacency formation. Although the neighbor state shows FULL, the DR/BDR election is affected. R1's point-to-point setting means it does not participate in DR election, and R2 expects a DR.

This can cause LSA flooding issues, and the area range summary may not be advertised correctly. The summary route is generated by the ABR, but if R1 is not an ABR (area 0 only), the range command has no effect. The root cause is that R1 is not an ABR, so area range does not apply.

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32
MCQmedium

A network engineer runs the following command to troubleshoot a Route Summarization issue: R1# debug eigrp packets EIGRP: Sending HELLO on Serial0/0/0 src 10.1.1.1, dst 224.0.0.10 EIGRP: Received UPDATE on Serial0/0/0 from 10.1.1.2 src 10.1.1.2, dst 224.0.0.10 update type: route prefix 10.0.0.0/16 metric 128576 EIGRP: Sending UPDATE on Serial0/0/0 to 10.1.1.2 update type: summary prefix 10.0.0.0/16 metric 128576 What does this output indicate?

A.R1 is receiving and re-advertising the summary route 10.0.0.0/16, likely configured with a summary address.
B.R1 is only receiving the summary route and not advertising it.
C.The summary route is being suppressed due to a route filter.
D.The summary route is learned via OSPF and redistributed into EIGRP.
AnswerA

The 'summary' update type indicates R1 is actively summarizing and advertising the route.

Why this answer

The debug output shows EIGRP packet exchanges. R1 receives an UPDATE for prefix 10.0.0.0/16 and then sends an UPDATE with type 'summary' for the same prefix. This indicates that R1 is both learning and advertising a summary route.

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33
MCQmedium

A network engineer runs the following command on Router R1: R1# show ip route 172.16.0.0 255.255.240.0 Routing entry for 172.16.0.0/20 Known via "ospf 1", distance 110, metric 20, type intra area Last update from 192.168.1.2 on GigabitEthernet0/0, 00:00:15 ago Routing Descriptor Blocks: * 192.168.1.2, from 192.168.1.2, 00:00:15 ago, via GigabitEthernet0/0 Route metric is 20, traffic share count is 1 Based on this output, what can be concluded about the route 172.16.0.0/20?

A.The route is a default route.
B.The route is an inter-area summary route.
C.The route is an external route.
D.The route is a connected route.
AnswerB

The metric of 20 and intra-area type suggest it is a summary route from an ABR (type 3 LSA).

Why this answer

The OSPF route is learned via intra-area (type intra area) with a metric of 20, which is characteristic of a summary LSA type 3, but the output shows intra area, indicating it is a summary route from an ABR.

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34
MCQhard

An engineer configures a DMVPN Phase 2 network. Spoke-to-spoke tunnels are not forming. Which is the most likely explanation?

A.NHRP redirect is not configured on the hub.
B.The spoke routers have different tunnel keys.
C.The NHRP authentication string is mismatched.
D.The IPsec transform-set is mismatched.
AnswerA

In Phase 2, the hub must send NHRP redirect messages to trigger spoke-to-spoke tunnel establishment. Without it, traffic will always go through the hub.

Why this answer

In DMVPN Phase 2, spoke-to-spoke tunnels require that the spoke routers have a route to the destination network via the tunnel interface, and that NHRP redirect is enabled on the hub. Without NHRP redirect, the hub will not send redirect messages to the spoke, and the spoke will not initiate a direct tunnel to the other spoke.

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35
MCQhard

A network engineer runs the following command on Router R1: R1# show ip route summary IP routing table maximum-paths: 32 IP routing table has 15 routes, using 900 bytes of memory Number of prefixes: /8: 1, /16: 2, /20: 3, /24: 9 Route types: Connected: 4, Static: 1, OSPF: 10 Route sources: OSPF: 10, Connected: 4, Static: 1 Based on this output, what is a potential issue regarding route summarization?

A.The routing table is too small.
B.There are too many /24 prefixes, suggesting poor summarization.
C.There are too many OSPF routes.
D.The routing table is empty.
AnswerB

Having 9 /24 prefixes indicates that more specific routes are present, and summarization could reduce the table size.

Why this answer

The routing table has many /24 prefixes (9), indicating that route summarization is not being used effectively, leading to a larger routing table.

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36
MCQmedium

A network engineer is troubleshooting an EIGRP network where route summarization is configured. Router R1 has the 'ip summary-address eigrp 100 10.0.0.0 255.0.0.0' command on its interface facing R2. After the configuration, R2 loses connectivity to the 10.1.0.0/16 subnet, which is one of the component routes. The engineer checks the routing table on R2 and sees the summary route 10.0.0.0/8 but not the specific route. What is the most likely cause?

A.The summary route 10.0.0.0/8 is being advertised with a metric of infinity, causing it to be ignored.
B.The 10.1.0.0/16 subnet is not directly connected to R1, so it cannot be summarized.
C.The summary address command was applied on the wrong interface, causing the summary to be sent out all interfaces, including the one facing the 10.1.0.0/16 subnet's origin.
D.The 10.1.0.0/16 subnet is not included in the summary range because the summary mask is /8, but the subnet's network address is 10.1.0.0, which is within the range, but the EIGRP process may have a split-horizon issue or the component route is not in the EIGRP topology table.
AnswerD

Correct. If the component route is not in the EIGRP topology table (e.g., due to a missing network statement or a passive interface), the summary route may still be generated, but the specific route is not advertised, causing loss of connectivity.

Why this answer

In EIGRP, the summary address command suppresses the advertisement of more specific routes and generates the summary. However, if the summary route is not installed in the routing table (e.g., due to a missing component), the specific routes may still be suppressed, causing a black hole.

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37
Drag & Dropmedium

Drag and drop the steps to verify and validate route summarization operational state into the correct order, from first to last.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps
Order
1Step 1
2Step 2
3Step 3
4Step 4
5Step 5

Why this order

Begin by checking the routing table on the summarizing router to see the summary route. Then, inspect the OSPF database to confirm the summary LSA. Next, verify that the summary is not causing suboptimal routing by checking for more specific routes.

After that, use show ip protocols to confirm summarization is enabled. Finally, test reachability to a host within the summarized range.

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38
MCQhard

An engineer configures mutual redistribution between OSPF and EIGRP on a router. After configuration, routing loops occur. Which is the most likely explanation?

A.The administrative distance of the redistributed routes is not modified, causing the redistributed route to be preferred over the original.
B.The seed metric is not configured for EIGRP redistribution.
C.The OSPF process ID is mismatched.
D.The redistribute command is missing the subnets keyword.
AnswerA

Without adjusting the administrative distance (e.g., using 'distance' command on redistributed routes), the redistributed route may have a lower AD than the original, leading to a routing loop.

Why this answer

Mutual redistribution without route tagging or filtering can cause routing loops. When a route redistributed from OSPF into EIGRP is then redistributed back into OSPF, it can be preferred over the original route if the administrative distance is lower, creating a loop. This is a classic edge case that requires careful use of route tags and distribute-lists.

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39
MCQmedium

A network engineer runs the following command on Router R1: R1# show ip eigrp interfaces detail GigabitEthernet0/0 IP-EIGRP interfaces for process 100 Interface Peers Xmit Queue Mean Pacing Time Multicast Pending Un/Reliable SRTT Un/Reliable Flow Timer Routes Gi0/0 1 0/0 10 0/10 50 0 Hello interval: 5 sec, Hold time: 15 sec Split horizon is enabled Summary address: 10.0.0.0/8 Next xmit serial <none> Un/reliable mcasts: 0/0 Un/reliable ucasts: 0/0 Mcast exceptions: 0 CR packets: 0 ACKs suppressed: 0 Retransmissions: 0 Retry timer: 15 Hello packets sent: 100, received: 99 Based on this output, what is the purpose of the summary address configured on this interface?

A.It filters all routes in the 10.0.0.0/8 range.
B.It advertises a summary route 10.0.0.0/8 to neighbors.
C.It redistributes connected routes.
D.It disables split horizon.
AnswerB

The summary address configuration causes R1 to advertise a summary route 10.0.0.0/8 on this interface.

Why this answer

The 'Summary address: 10.0.0.0/8' line shows that a manual summary route is configured on this interface, which will be advertised to EIGRP neighbors.

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40
Multi-Selectmedium

Which TWO commands can be used to verify route summarization on a Cisco router running OSPF? (Choose TWO.)

Select 2 answers
A.show ip route summary
B.show ip ospf border-routes
C.show ip protocols
D.show ip route
E.show ip ospf database
AnswersA, B

This command provides a summary of the routing table, including the number of routes and memory usage, which helps verify summarization.

Why this answer

The 'show ip route summary' command provides a summary of the routing table including the number of routes and the memory used, while 'show ip ospf border-routes' displays the OSPF route table entries for ABRs and ASBRs, which can include summary routes. 'show ip protocols' does not directly show summarization details. 'show ip route' alone does not summarize. 'show ip ospf database' shows the LSDB, not the summarized routing table.

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41
Multi-Selectmedium

Which TWO statements about route summarization in BGP are true? (Choose TWO.)

Select 2 answers
A.The 'aggregate-address' command creates a summary route in the BGP table.
B.The 'summary-only' keyword can be used with 'aggregate-address' to suppress more specific routes.
C.The 'network' command is used to create a summary route in BGP.
D.BGP summarization requires a route-map to suppress more specific routes.
E.Route summarization in BGP can only be configured on route reflectors.
AnswersA, B

This command is used to create an aggregate route in BGP, which can then be advertised to peers.

Why this answer

In BGP, the 'aggregate-address' command creates a summary route in the BGP table, and it can suppress more specific routes using the 'summary-only' keyword. The 'network' command is used to advertise a specific prefix, not to summarize. The 'aggregate-address' command does not require a route-map to suppress specifics; the 'summary-only' keyword does that.

BGP summarization can be done on any BGP speaker, not just route reflectors.

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42
MCQmedium

A network engineer runs the following command to troubleshoot a Route Summarization issue: R1# debug ip routing IP: route table change: 10.0.0.0/16 via 10.1.1.2, Serial0/0/0, distance 90, metric 128576 IP: route table change: 10.0.1.0/24 via 10.1.1.2, Serial0/0/0, distance 90, metric 128576 IP: route table change: 10.0.2.0/24 via 10.1.1.2, Serial0/0/0, distance 90, metric 128576 What does this output indicate?

A.Both the summary route 10.0.0.0/16 and more specific /24 routes are being installed, which could indicate that summarization is not properly filtering the specific routes.
B.Only the summary route is being installed, and the /24 routes are being ignored.
C.The summary route is being replaced by the more specific routes.
D.The routes are being learned via different routing protocols.
AnswerA

The presence of both summary and specific routes suggests that the summary is not suppressing the specifics.

Why this answer

The debug output shows that multiple routes (a /16 and two /24s) are being installed into the routing table via the same next hop. This indicates that both the summary route and more specific routes are present, which may be a sign of inconsistent summarization or a leak of more specific routes.

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44
MCQmedium

A network engineer runs the following command to troubleshoot a Route Summarization issue: R1# show ip nhrp detail 10.0.0.0/16 via 10.1.1.2, Tunnel0 created 00:01:00, expire 01:59:00 Type: summary, Flags: used NBMA address: 192.168.1.2 Registration: never What does this output indicate?

A.The summary route 10.0.0.0/16 is learned via NHRP and is active, with the next hop being 192.168.1.2 over Tunnel0.
B.The summary route is not being used because the 'used' flag is not set.
C.The summary route is learned via EIGRP, not NHRP.
D.The summary route is a static route configured on the router.
AnswerA

The 'summary' type and 'used' flag confirm this is an active NHRP summary route.

Why this answer

This output shows an NHRP cache entry for the summary route 10.0.0.0/16. The type is 'summary', indicating that this is a summary route learned via NHRP. The 'used' flag and NBMA address show that the route is active and pointing to a specific tunnel destination.

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45
MCQhard

A redistribution setup between OSPF and EIGRP is causing a routing loop for subnet 10.1.1.0/24. Router R1 runs OSPF and EIGRP with redistribution. R1's configuration: router ospf 1 redistribute eigrp 100 subnets ! router eigrp 100 redistribute ospf 1 metric 10000 100 255 1 1500 ! interface GigabitEthernet0/0 ip address 10.1.1.1 255.255.255.0 ip summary-address eigrp 100 10.1.0.0 255.255.255.0 ! Router R2 (EIGRP neighbor) shows: R2# show ip route 10.1.1.0 Routing entry for 10.1.0.0/24, supernet Known via "eigrp 100", distance 90, metric 30720, type internal Last update from 10.1.1.1 on GigabitEthernet0/0, 00:00:05 ago What is the root cause?

A.The summary route 10.1.0.0/24 is less specific and can cause routing loops when combined with redistribution because R2 may send traffic for 10.1.1.0/24 back to R1.
B.The redistribution metric is too high, causing EIGRP to prefer the OSPF route via another path.
C.OSPF does not support subnets keyword, so the route is not redistributed correctly.
D.EIGRP is not enabled on the interface, so the summary is not advertised.
AnswerA

The summary creates a less specific route that can be redistributed, leading to a loop.

Why this answer

The summary route 10.1.0.0/24 is being advertised via EIGRP, but it is a less specific prefix than the actual /24. When R1 redistributes OSPF into EIGRP, the summary may cause R2 to prefer the summary over a more specific route, and if R2 sends traffic back to R1 for 10.1.1.0/24, R1 might forward it to R2 again if the OSPF route is not present, creating a loop. The summary should match the exact subnet or be more specific to avoid loops.

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46
Multi-Selecthard

Which TWO statements about route summarization in EIGRP are true? (Choose TWO.)

Select 2 answers
A.EIGRP automatic summarization is enabled by default for classful networks.
B.Manual summarization can be configured using the 'ip summary-address eigrp' command under interface configuration.
C.EIGRP supports automatic summarization for all types of networks, including discontiguous subnets.
D.Route summarization in EIGRP requires the use of a route-map to define the summary prefix.
E.Manual summarization can only be applied to serial interfaces.
AnswersA, B

By default, EIGRP summarizes routes at classful boundaries when automatic summarization is enabled.

Why this answer

EIGRP supports manual summarization on any interface using the 'ip summary-address eigrp' command, and automatic summarization is enabled by default for classful networks. EIGRP does not support automatic summarization at the classful boundary for all networks; it is only for major network boundaries. Summarization in EIGRP does not require a route-map, and it can be configured on any interface, not just serial interfaces.

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47
MCQhard

A network engineer runs the following command on Router R1: R1# show ip bgp neighbors 10.1.1.1 advertised-routes BGP table version is 10, local router ID is 1.1.1.1 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter, x best-external, a additional-path, c RIB-compressed, Origin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path *> 10.0.0.0/8 0.0.0.0 0 32768 i *> 10.1.0.0/16 0.0.0.0 0 32768 i *> 10.1.1.0/24 0.0.0.0 0 32768 i *> 10.1.2.0/24 0.0.0.0 0 32768 i Based on this output, what is a problem with the BGP advertisements?

A.The router is not advertising any routes.
B.The router is advertising overlapping prefixes, including both summary and specific routes.
C.The router is only advertising the summary route.
D.The router is using incorrect next-hop.
AnswerB

The presence of 10.0.0.0/8 and more specific prefixes like 10.1.1.0/24 indicates overlapping advertisements, which is inefficient.

Why this answer

The router is advertising both a summary route (10.0.0.0/8) and more specific routes (10.1.0.0/16, 10.1.1.0/24, etc.), which defeats the purpose of summarization and can cause routing loops or suboptimal routing.

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48
Drag & Dropmedium

Drag and drop the steps to configure OSPF inter-area summarization on an ABR into the correct order, from first to last.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps
Order
1Step 1
2Step 2
3Step 3
4Step 4
5Step 5

Why this order

First, enter OSPF configuration mode for the process. Then, configure the area where the routes originate. Next, apply the range command to summarize prefixes into that area.

After that, verify the summary route is present in the routing table. Finally, check that the summary is advertised to neighboring areas.

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49
MCQmedium

A network engineer runs the following command to troubleshoot a Route Summarization issue: R1# show ip eigrp topology 10.0.0.0/16 IP-EIGRP topology entry for 10.0.0.0/16 State is Passive, Query origin flag is 1, 1 Successor(s), FD is 128576 Routing Descriptor Blocks: 10.1.1.2 (Serial0/0/0), from 10.1.1.2, Send flag is 0x0 Composite metric is (128576/156160), Route is Internal Vector metric: Minimum bandwidth is 10000 Kbit Total delay is 2000 microseconds Reliability is 255/255 Load is 1/255 Minimum MTU is 1500 Hop count is 2 What does this output indicate?

A.The summary route 10.0.0.0/16 is installed in the routing table and reachable via 10.1.1.2.
B.The summary route is in active state, indicating a query is in progress.
C.The summary route is not being advertised because the FD is too high.
D.The summary route is learned via redistribution, not summarization.
AnswerA

The output shows a valid successor and passive state, confirming the route is installed and reachable.

Why this answer

This output shows the EIGRP topology table entry for the summary route 10.0.0.0/16. The state is Passive, meaning the route is stable and reachable. The presence of a successor and the metric details indicate that the summary route is being advertised and learned via EIGRP.

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50
MCQmedium

A network engineer runs the following command to troubleshoot a Route Summarization issue: R1# show ip bgp 10.0.0.0/16 BGP routing table entry for 10.0.0.0/16, version 2 Paths: (1 available, best #1, table default) Advertised to update-groups: 1 Refresh Epoch 1 Local, (aggregated by 65000 1.1.1.1) 10.1.1.2 from 10.1.1.2 (2.2.2.2) Origin IGP, metric 0, localpref 100, valid, external, best Atomic-aggregate What does this output indicate?

A.The route 10.0.0.0/16 is an aggregate route, and the atomic-aggregate attribute indicates that the AS path may be incomplete.
B.The route is a normal BGP learned route without summarization.
C.The route is suppressed and not advertised to neighbors.
D.The route is learned via redistribution from OSPF.
AnswerA

The 'aggregated' keyword and 'Atomic-aggregate' attribute confirm this is a summary route with potential AS path loss.

Why this answer

This output shows the BGP table entry for prefix 10.0.0.0/16. The path is marked as 'aggregated', indicating it is a summary route. The 'Atomic-aggregate' attribute suggests that the route is an aggregate and may have lost some AS path information.

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51
MCQmedium

A network engineer is troubleshooting a connectivity issue between two branches connected via a WAN link. Router R1 (10.1.0.0/16) is summarizing its directly connected subnets (10.1.1.0/24, 10.1.2.0/24, 10.1.3.0/24) as a single 10.1.0.0/16 route to Router R2 via EIGRP. Users at R2 report that they cannot reach the 10.1.4.0/24 subnet, which was recently added to R1. What is the most likely cause of the problem?

A.The summary route 10.1.0.0/16 was configured manually, and the new subnet 10.1.4.0/24 is not within the summary range because the mask is too specific.
B.The new subnet 10.1.4.0/24 was not advertised because the summary address command suppresses more specific routes, but the summary itself is not being generated due to a missing network statement under the EIGRP process.
C.The WAN link is down, causing R2 to lose the summary route.
D.The engineer forgot to configure the summary address on the interface facing R2 for the new subnet.
AnswerB

Correct. In EIGRP, a manually configured summary address suppresses the advertisement of more specific routes and generates the summary only if the component routes exist. If the new subnet is not in the EIGRP network, the summary may not be generated or the specific route is missing.

Why this answer

The summary route 10.1.0.0/16 includes the new subnet 10.1.4.0/24, but the issue indicates that the summary is not being updated or is too broad, causing a mismatch. The most likely cause is that the summary address was configured manually and does not automatically include new subnets unless the summary range is adjusted.

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52
MCQeasy

What is the default OSPF reference bandwidth used in the cost calculation formula on Cisco IOS?

A.10 Mbps
B.100 Mbps
C.1000 Mbps
D.1 Gbps
AnswerB

Cisco IOS uses 100 Mbps as the reference bandwidth by default.

Why this answer

The default reference bandwidth is 100 Mbps, meaning the cost is calculated as 100,000,000 / interface bandwidth in bps.

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53
MCQeasy

What is the maximum hop count for a route in RIPv2 by default?

A.15
B.16
C.255
D.32
AnswerA

15 is the maximum metric; 16 means infinity (unreachable).

Why this answer

RIP uses a maximum hop count of 15, with 16 considered unreachable, to prevent routing loops.

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54
MCQhard

A network engineer is troubleshooting a redistribution issue between EIGRP and OSPF. Router R1 redistributes EIGRP routes into OSPF. The engineer configured a summary route 10.0.0.0/8 using the 'summary-address' command under the OSPF process. After the configuration, OSPF neighbors lose connectivity to the 10.1.0.0/16 subnet, which is one of the component routes. What is the most likely cause?

A.The summary-address command on R1 is configured with the 'tag' keyword, causing the summary to be ignored by other routers.
B.The summary route 10.0.0.0/8 is not being generated because the component routes are not all present in the OSPF database.
C.The OSPF neighbor relationship is down due to a mismatch in area IDs.
D.The engineer forgot to configure the 'network' command for the summary route under OSPF.
AnswerB

Correct. In OSPF, the summary-address command generates a summary only if at least one component route exists in the OSPF database. If the component route is missing due to redistribution issues, the summary may not be generated, and the specific routes may be suppressed.

Why this answer

The issue is that the summary-address command in OSPF can suppress the advertisement of more specific routes, but if the summary route is not installed due to a missing component or metric issue, it can cause a routing black hole.

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56
MCQmedium

A network engineer runs the following command on Router R1: R1# show ip eigrp topology 10.0.0.0 255.255.252.0 IP-EIGRP (AS 100): Topology entry for 10.0.0.0/22 State: Passive, Origin: Internal, Metric [90/2172416], Tag 0 Number of successors: 1 FD is 2172416, Serno: 5 Route is Summary Advertised by R2 (via Serial0/0/0) Reply status: 0 Based on this output, what is true about the route 10.0.0.0/22?

A.The route is a summary route generated by R1.
B.The route is a summary route learned from R2.
C.The route is an external route redistributed into EIGRP.
D.The route is in active state and being queried.
AnswerB

The output shows 'Advertised by R2' and 'Route is Summary', indicating it is a summary route received from neighbor R2.

Why this answer

The 'Route is Summary' line indicates this is a summary route in the EIGRP topology table. The output shows it is passive and has a successor, confirming it is a valid summary route.

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57
MCQmedium

A network engineer is troubleshooting BGP route summarization on a border router that advertises a summary route 172.16.0.0/16 to an ISP neighbor. The engineer notices that the ISP is receiving the summary route but also receiving the more specific routes (172.16.1.0/24, 172.16.2.0/24), causing suboptimal routing. What should the engineer do to ensure only the summary route is advertised?

A.Configure the 'network' command for the summary route and remove the network statements for the specific subnets.
B.Use the 'aggregate-address 172.16.0.0 255.255.0.0 summary-only' command under the BGP process.
C.Apply a route-map to the neighbor to filter out the specific routes using an ACL.
D.Configure the 'summary-address' command under the BGP process.
AnswerB

Correct. The aggregate-address with summary-only keyword creates the summary and suppresses all more specific routes from being advertised.

Why this answer

In BGP, to suppress more specific routes when advertising a summary, the engineer must use the 'aggregate-address' command with the 'summary-only' keyword.

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58
MCQmedium

A network engineer runs the following command to troubleshoot a Route Summarization issue: R1# show ip ospf database summary 10.0.0.0 OSPF Router with ID (1.1.1.1) (Process ID 1) Summary Net Link States (Area 0) LS age: 100 Options: (No TOS-capability, DC) LS Type: Summary Links(Network) Link State ID: 10.0.0.0 (summary Network Number) Advertising Router: 2.2.2.2 LS Seq Number: 80000001 Checksum: 0x1234 Length: 28 Network Mask: /16 TOS: 0 Metric: 20 What does this output indicate?

A.The summary route 10.0.0.0/16 is being advertised by router 2.2.2.2 as a Type 3 LSA into Area 0.
B.The summary route is a Type 5 external LSA from an ASBR.
C.The summary route is a Type 1 router LSA from router 2.2.2.2.
D.The summary route is not installed because the metric is too high.
AnswerA

The LS Type and advertising router confirm it is a Type 3 summary LSA.

Why this answer

This output shows the OSPF database entry for a summary route 10.0.0.0/16. The LS Type is Summary Links, indicating it is a Type 3 LSA generated by an ABR (advertising router 2.2.2.2). The metric of 20 suggests it is a summary route injected into Area 0.

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59
MCQhard

DMVPN spoke-to-spoke tunnel failures are occurring due to route summarization. Hub router R1 has: interface Tunnel0 ip address 172.16.0.1 255.255.255.0 ip nhrp network-id 1 ip nhrp map multicast dynamic tunnel source GigabitEthernet0/0 tunnel mode gre multipoint ! router eigrp 100 network 172.16.0.0 ! Spoke R2 has: interface Tunnel0 ip address 172.16.0.2 255.255.255.0 ip nhrp network-id 1 ip nhrp nhs 172.16.0.1 tunnel source GigabitEthernet0/0 tunnel mode gre multipoint ! R1 also has: interface GigabitEthernet0/0 ip summary-address eigrp 100 10.0.0.0 255.255.252.0 ! Spokes cannot establish direct tunnels to each other for subnets within 10.0.0.0/22. What is the root cause?

A.The summary route causes spokes to forward traffic to the hub instead of establishing direct tunnels, as the summary is preferred over more specific routes.
B.NHRP is not configured correctly on the spokes, so they cannot register.
C.EIGRP is not enabled on the tunnel interface, so routes are not exchanged.
D.The tunnel mode is not multipoint on the spokes.
AnswerA

Spokes use the summary route to reach the hub, bypassing NHRP redirect.

Why this answer

The summary route 10.0.0.0/22 is advertised by R1 to all spokes. When a spoke wants to reach a subnet within that summary on another spoke, it sends traffic to R1 (the summary route) instead of using the NHRP redirect to establish a spoke-to-spoke tunnel. The summary overrides the more specific routes that would trigger NHRP redirects.

The fix is to use a leak-map to advertise specific routes or disable summarization.

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60
MCQhard

An engineer configures EIGRP named mode on a router. After configuration, a directly connected EIGRP neighbor is not forming an adjacency. 'show ip eigrp neighbors' shows nothing. Which is the most likely explanation?

A.The 'network' command was used under the EIGRP process, but the 'af-interface' configuration was omitted.
B.The EIGRP autonomous system number is mismatched.
C.The K-values are mismatched between the routers.
D.The passive-interface default command is configured.
AnswerA

In named mode, the 'af-interface' command is required to enable EIGRP on an interface; the 'network' command alone does not activate the interface.

Why this answer

In EIGRP named mode, the network statement is not used. Instead, the 'af-interface' configuration under the address-family is mandatory to enable EIGRP on an interface. If the engineer only uses the classic 'network' command under the router eigrp process (which is still accepted in named mode for backward compatibility but does not activate the interface), the interface will not be enabled for EIGRP.

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61
MCQmedium

A network engineer runs the following command to troubleshoot a Route Summarization issue: R1# show ip route summary IP routing table maximum-paths limit: 32 IP routing table entry count: 15 IP routing table active entry count: 15 Number of prefixes: 15 Number of /0: 0 Number of /8: 1 Number of /16: 2 Number of /24: 12 Number of /32: 0 What does this output indicate?

A.The routing table contains 2 /16 summary routes, likely summarizing the 12 /24 subnets, indicating successful route summarization.
B.The routing table has no summarization, as all routes are /24 or smaller.
C.The routing table is full and cannot accept more routes.
D.The summary routes are not being used because they are inactive.
AnswerA

The presence of fewer /16 routes than /24 routes suggests summarization is working.

Why this answer

This output shows a summary of the IP routing table. The prefix length distribution indicates that there are 2 /16 routes and 12 /24 routes. This suggests that route summarization is in effect, as the /16 routes likely summarize the /24 subnets.

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62
MCQmedium

Given the following OSPF configuration on router R2: router ospf 1 network 10.0.0.0 0.255.255.255 area 0 area 0 range 10.0.0.0 255.255.252.0 Which statement is true about this configuration?

A.Router R2 will advertise a summary route 10.0.0.0/22 into area 0 from other areas.
B.Router R2 will summarize routes from area 0 into other areas.
C.Router R2 will create a static route for 10.0.0.0/22.
D.Router R2 will filter all routes not within 10.0.0.0/22.
AnswerA

Correct. The area range command on an ABR summarizes routes from other areas into area 0.

Why this answer

The 'area range' command is used for inter-area route summarization on an ABR. It summarizes routes from one area into another, but only if the router is an ABR.

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63
MCQmedium

Which of the following best describes the behavior of BGP when an 'aggregate-address' command is used without the 'summary-only' keyword?

A.The aggregate route is advertised, and all more specific routes are also advertised.
B.Only the aggregate route is advertised.
C.The aggregate route is not advertised unless a network command exists for it.
D.The more specific routes are withdrawn from the BGP table.
AnswerA

Correct. Without summary-only, both aggregate and specifics are advertised.

Why this answer

Without the summary-only keyword, BGP advertises both the aggregate route and the more specific routes that are in the BGP table.

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64
MCQmedium

Which EIGRP packet type is used to confirm receipt of a route update during reliable transport?

A.Hello
B.Update
C.ACK
D.Query
AnswerC

ACK packets are Hello packets with no data, used to acknowledge received updates.

Why this answer

EIGRP uses ACK packets (which are Hello packets with no data) to acknowledge reliable updates.

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65
MCQeasy

In OSPF, what is the default metric for a Type 3 summary LSA generated by an ABR using the 'area range' command?

A.The lowest metric among the summarized routes.
B.The highest metric among the summarized routes.
C.The sum of all metrics.
D.The metric is set to 1 by default.
AnswerA

Correct. OSPF uses the best (lowest) metric from the component routes for the summary LSA.

Why this answer

The default metric for a Type 3 summary LSA is the lowest metric among the component routes being summarized.

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66
MCQmedium

Given this partial configuration on router R6: router bgp 65000 neighbor 192.168.1.1 remote-as 65001 address-family ipv4 network 172.16.0.0 mask 255.255.0.0 aggregate-address 172.16.0.0 255.255.0.0 What is missing if the administrator wants to ensure that only the aggregate route is advertised to neighbor 192.168.1.1?

A.The 'summary-only' keyword is missing from the aggregate-address command.
B.The 'network' command should be removed.
C.The 'synchronization' command must be enabled.
D.The 'neighbor 192.168.1.1 route-map' command is needed.
AnswerA

Correct. Without summary-only, more specific routes are still advertised.

Why this answer

The aggregate-address command without the summary-only keyword will advertise both the aggregate and the more specific routes. To suppress the specifics, the summary-only keyword is required.

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67
Multi-Selectmedium

Which TWO configuration steps are required to implement manual route summarization in OSPF on an ABR? (Choose TWO.)

Select 2 answers
A.Configure the 'area area-id range network mask' command under router OSPF configuration.
B.Ensure the summary address is a supernet of the networks being summarized.
C.Use the 'summary-address network mask' command under router OSPF configuration.
D.Apply the 'ip summary-address ospf' command under the interface connecting to the backbone.
E.Configure a 'network' statement that matches the summary address.
AnswersA, B

This command creates a summary route for networks in the specified area, which is the correct method for ABR summarization.

Why this answer

In OSPF, manual summarization on an ABR is done using the 'area range' command under router configuration mode, which summarizes routes from one area into another. The summary address must be within the range of networks in the area. The 'summary-address' command is used for external routes on ASBRs, not for inter-area summarization. 'network' commands define interfaces, not summarization. 'default-information originate' is for default routes.

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68
MCQhard

EIGRP stuck-in-active (SIA) is occurring due to route summarization. Router R1 is the hub in a hub-and-spoke topology with R2 and R3 as spokes. R1's configuration: interface GigabitEthernet0/0 ip address 10.0.0.1 255.255.255.0 ip summary-address eigrp 100 10.0.0.0 255.255.252.0 ! router eigrp 100 network 10.0.0.0 ! R2 and R3 are connected via Frame Relay. R2 shows: R2# show ip eigrp topology 10.0.1.0/24 P 10.0.1.0/24, 1 successors, FD is 30720 via 10.0.0.1 (30720/28160), GigabitEthernet0/0 R3 has a similar entry. However, when R1's summary is active, R2 and R3 go into active state for the summary. What is the root cause?

A.The summary route causes EIGRP queries to loop between spokes when one loses connectivity, leading to SIA.
B.The Frame Relay network is not supporting multicast, so EIGRP hello packets are lost.
C.The summary route metric is too high, causing EIGRP to not install it.
D.EIGRP is not enabled on the spoke interfaces.
AnswerA

Spokes query each other for the summary, and if neither has a route, they query the hub again, causing a loop.

Why this answer

The summary route 10.0.0.0/22 is advertised by R1 to both spokes. If one spoke loses connectivity to R1, it queries the other spoke for the summary. The spoke may not have a route to the summary, causing it to query R1 again, leading to a query loop and SIA.

The summary should be configured with a leak-map to allow specific routes, or the query scope should be limited.

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69
MCQhard

An engineer configures a BGP route reflector in a network. After configuration, some iBGP routes are being dropped, causing routing loops. Which is the most likely explanation?

A.The route reflector is configured with the same cluster ID as another route reflector in the same AS.
B.The next-hop-self command is not configured on the route reflector.
C.The BGP synchronization rule is enabled.
D.The route reflector is not a client of itself.
AnswerA

If two route reflectors share the same cluster ID, a route reflected by one may be dropped by the other because it sees its own cluster ID in the CLUSTER_LIST, preventing proper propagation and potentially causing loops.

Why this answer

BGP route reflectors use the ORIGINATOR_ID and CLUSTER_LIST attributes to prevent loops. If a route reflector receives a route with its own CLUSTER_LIST or ORIGINATOR_ID, it will drop the route. This can happen if there is a misconfiguration where the route reflector's cluster ID is not unique, or if a route reflector reflects a route back to the client that originated it, causing a loop.

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70
MCQhard

An ACL implicit deny is blocking management traffic due to route summarization. Router R1 has: access-list 100 permit ip 10.0.0.0 0.0.3.255 any ! interface GigabitEthernet0/0 ip access-group 100 in ! router eigrp 100 network 10.0.0.0 ! R1 also has: interface GigabitEthernet0/1 ip address 192.168.1.1 255.255.255.0 ip summary-address eigrp 100 10.0.0.0 255.255.252.0 ! A management station at 10.0.1.100 cannot SSH to R1's loopback 0 (10.0.0.1). What is the root cause?

A.The summary route changes the return path for traffic to the management station, and the return interface has an ACL with implicit deny blocking the SSH reply.
B.The ACL does not permit SSH traffic (port 22).
C.The summary route is not installed, so traffic is dropped.
D.EIGRP is not advertising the loopback route.
AnswerA

The summary can cause asymmetric routing, and the return path ACL blocks the traffic.

Why this answer

The ACL permits traffic from 10.0.0.0/22 (10.0.0.0-10.0.3.255) to any, but the summary route is also 10.0.0.0/22. However, the ACL is applied inbound on GigabitEthernet0/0. The management station's traffic comes from 10.0.1.100, which is within the permitted range, so the ACL should allow it.

But the summary route may cause the return traffic to be sent via a different interface, and if that interface has an ACL with implicit deny, the SSH session fails. The root cause is that the summary route changes the path, and the return path has an ACL blocking traffic.

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71
MCQhard

An engineer configures unicast Reverse Path Forwarding (uRPF) in strict mode on an interface. After configuration, legitimate traffic from a directly connected network is being dropped. Which is the most likely explanation?

A.Asymmetric routing is causing the return path to use a different interface.
B.The 'allow-default' option is not configured, and a default route exists.
C.The interface is configured with an IP address that is not in the routing table.
D.The routing table has a more specific route for the source network via a different interface.
AnswerA

Strict uRPF requires the source IP to be reachable via the same interface it arrived on. Asymmetric routing violates this, causing drops.

Why this answer

Strict uRPF checks that the source IP address of incoming packets has a route in the routing table that points back to the same interface. If there is asymmetric routing where the return path uses a different interface, strict uRPF will drop the traffic. This is a common edge case in networks with multiple paths.

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72
MCQhard

An engineer configures Control Plane Policing (CoPP) on a router. After configuration, OSPF neighbors are flapping. Which is the most likely explanation?

A.The class-default is configured with a police action that drops OSPF packets exceeding the rate.
B.The CoPP policy is applied to the wrong direction (input vs output).
C.The access-list used to classify OSPF packets is missing the 'permit' statement for OSPF protocol.
D.The CoPP policy uses 'drop' action for OSPF class.
AnswerA

If OSPF packets are not explicitly classified and permitted, they fall into class-default. The police action in class-default will drop packets that exceed the configured rate, causing OSPF hello packets to be dropped and neighbors to flap.

Why this answer

CoPP applies a policy-map to the control plane. If the default class-default is used without an explicit permit for OSPF packets, the implicit deny at the end of the policy-map will drop OSPF packets. The default class-default action is 'drop' if not explicitly configured, but even if a 'police' action is configured, the default behavior is to drop packets that exceed the rate.

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73
Multi-Selecthard

Which TWO statements correctly describe the verification of route summarization using Cisco IOS commands? (Choose TWO.)

Select 3 answers
A.The 'show ip route' command displays the summary route with a next-hop of Null0 for EIGRP and OSPF summarization.
B.The 'show ip eigrp topology' command displays all configured summary addresses and their metrics.
C.The 'show ip protocols' command lists the configured summary-address ranges under each routing process.
D.The 'debug ip routing' command provides detailed information about summary route creation and suppression.
E.The 'show ip ospf database summary' command displays the Type 3 LSAs, including those generated by the 'area range' command.
AnswersA, C, E

Correct. Both EIGRP and OSPF install a discard route (to Null0) for the summary prefix to prevent loops, visible in 'show ip route'.

Why this answer

To verify route summarization, engineers use 'show ip route' to see the summary route and discard entry, 'show ip protocols' to view configured summary addresses, and 'show ip ospf database' to see Type 3 summary LSAs. The 'show ip eigrp topology' command does not show summary routes by default, and 'debug ip routing' shows routing table changes but not summary-specific events.

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74
MCQmedium

A network engineer runs the following command to troubleshoot a Route Summarization issue: R1# show mpls ldp bindings 10.0.0.0/16 tib entry: 10.0.0.0/16, rev 1 local binding: label: 16 remote binding: lsr: 2.2.2.2:0, label: 17 What does this output indicate?

A.The summary route 10.0.0.0/16 has both a local and remote label binding, indicating MPLS LDP is operational for this prefix.
B.The summary route is not label-switched because no local binding exists.
C.The remote binding indicates that the route is not being summarized.
D.The label bindings are for the more specific /24 routes, not the summary.
AnswerA

The presence of both local and remote bindings confirms LDP is working for the summary route.

Why this answer

This output shows MPLS LDP label bindings for the prefix 10.0.0.0/16. There is a local label (16) and a remote label (17) from LSR 2.2.2.2. This indicates that the summary route is label-switched, and LDP has successfully assigned labels for it.

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75
MCQhard

CoPP rate-limit is impacting legitimate traffic due to route summarization. Router R1 has: access-list 100 permit ip 10.0.0.0 0.0.3.255 any ! class-map match-all COPP-CLASS match access-group 100 ! policy-map COPP-POLICY class COPP-CLASS police 10000 conform-action transmit exceed-action drop ! control-plane service-policy input COPP-POLICY ! router eigrp 100 network 10.0.0.0 ! interface GigabitEthernet0/0 ip summary-address eigrp 100 10.0.0.0 255.255.252.0 ! R2 (10.0.1.1) sends EIGRP packets to R1, but they are being dropped. What is the root cause?

A.The CoPP policy matches EIGRP traffic from the summarized range and polices it, causing EIGRP packets to be dropped.
B.The summary route causes EIGRP to send packets to the control plane at a high rate, exceeding the policer.
C.EIGRP is not enabled on the interface, so packets are dropped.
D.The control-plane policy is applied in the wrong direction.
AnswerA

EIGRP packets are within the ACL range and are rate-limited.

Why this answer

The CoPP policy matches traffic from 10.0.0.0/22 and polices it to 10 kbps. EIGRP packets from R2 (10.0.1.1) are within this range and are subject to policing. If the EIGRP traffic rate exceeds 10 kbps, packets are dropped, causing neighbor flapping.

The summary route itself does not cause the drop, but the CoPP policy inadvertently includes EIGRP traffic. The fix is to create a separate class for EIGRP or adjust the ACL.

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