300-410 Route Summarization — Timed 20 Questions

Question 1

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?

Accepted Answer

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.. 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.

Answer

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.

Answer

The WAN link is down, causing R2 to lose the summary route.

Answer

The engineer forgot to configure the summary address on the interface facing R2 for the new subnet.

Question 2

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?

Accepted Answer

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.. 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.

Answer

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.

Answer

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.

Answer

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.

Question 3

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?

Accepted Answer

Use the 'aggregate-address 172.16.0.0 255.255.0.0 summary-only' command under the BGP process.. In BGP, to suppress more specific routes when advertising a summary, the engineer must use the 'aggregate-address' command with the 'summary-only' keyword.

Answer

Configure the 'network' command for the summary route and remove the network statements for the specific subnets.

Answer

Apply a route-map to the neighbor to filter out the specific routes using an ACL.

Answer

Configure the 'summary-address' command under the BGP process.

Question 4

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?

Accepted Answer

The summary route 10.0.0.0/8 is not being generated because the component routes are not all present in the OSPF database.. 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.

Answer

The summary-address command on R1 is configured with the 'tag' keyword, causing the summary to be ignored by other routers.

Answer

The OSPF neighbor relationship is down due to a mismatch in area IDs.

Answer

The engineer forgot to configure the 'network' command for the summary route under OSPF.

Question 5

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?

Accepted Answer

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.. 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.

Answer

The 192.168.1.0/24 subnet is not directly connected to R1, so it cannot be summarized.

Answer

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.

Answer

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.

Question 6

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?

Accepted Answer

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.. 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.

Answer

The summary route 10.0.0.0/16 is being advertised with a metric of 0, causing routers to prefer a default route instead.

Answer

The ABR is not generating the summary route because the component routes are not all in the same area.

Answer

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.

Question 7

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?

Accepted Answer

Add the 'summary-only' keyword to the aggregate-address command.. 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.

Answer

Remove the network statements for the specific subnets from the BGP process.

Answer

Configure a route-map to set a higher local preference on the aggregate route.

Answer

Use the 'aggregate-address' command with the 'as-set' keyword.

Question 8

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?

Accepted Answer

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.. 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.

Answer

The summary route 10.0.0.0/8 is being advertised with a metric of infinity, causing it to be ignored.

Answer

The 10.1.0.0/16 subnet is not directly connected to R1, so it cannot be summarized.

Answer

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.

Question 9

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?

Accepted Answer

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.. 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.

Answer

The OSPFv3 process is not enabled on the interface facing the 2001:db8:0:1:1::/80 subnet.

Answer

The summary-address command should be applied on the interface, not under the OSPFv3 process.

Answer

The 2001:db8:0:1:1::/80 subnet is not in the OSPFv3 database because it is redistributed from another protocol.

Question 10

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?

Accepted Answer

The route is a summary route learned from R2.. 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.

Answer

The route is a summary route generated by R1.

Answer

The route is an external route redistributed into EIGRP.

Answer

The route is in active state and being queried.

Question 11

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?

Accepted Answer

The route is an inter-area summary route.. 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.

Answer

The route is a default route.

Answer

The route is an external route.

Answer

The route is a connected route.

Question 12

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?

Accepted Answer

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

Answer

The route is a learned route from AS 65002.

Answer

The route is a default route.

Answer

The route is suppressed.

Question 13

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?

Accepted Answer

It advertises a summary route 10.0.0.0/8 to neighbors.. 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.

Answer

It filters all routes in the 10.0.0.0/8 range.

Answer

It redistributes connected routes.

Answer

It disables split horizon.

Question 14

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?

Accepted Answer

It is a summary route for 172.16.0.0/20 advertised by ABR 2.2.2.2.. 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.

Answer

It is a router LSA from R1.

Answer

It is an external route from ASBR.

Answer

It is a network LSA for the 172.16.0.0 network.

Question 15

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?

Accepted Answer

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

Answer

The routing table is too small.

Answer

There are too many OSPF routes.

Answer

The routing table is empty.

Question 16

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?

Accepted Answer

The router is advertising overlapping prefixes, including both summary and specific routes.. 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.

Answer

The router is not advertising any routes.

Answer

The router is only advertising the summary route.

Answer

The router is using incorrect next-hop.

Question 17

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?

Accepted Answer

The summary route is not suppressing the more specific route 10.0.1.0/24.. 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.

Answer

The summary route is working correctly and suppressing all specifics.

Answer

The summary route has a better metric than the specific route.

Answer

The summary route is not installed in the routing table.

Question 18

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?

Accepted Answer

It is a discard route to prevent routing loops.. 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.

Answer

It is a default route for unknown destinations.

Answer

It is a route learned from a neighbor.

Answer

It is a connected route.

Question 19

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?

Accepted Answer

It creates a summary route 10.0.0.0/24 with an administrative distance of 5, advertised out all EIGRP-enabled interfaces.. 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.

Answer

It creates a summary route 10.0.0.0/24 and sets the metric to 5.

Answer

It creates a summary route 10.0.0.0/24 and suppresses more specific routes with a metric of 5.

Answer

It creates a summary route 10.0.0.0/24 with a tag of 5.

Question 20

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?

Accepted Answer

Router R2 will advertise a summary route 10.0.0.0/22 into area 0 from other areas.. 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.

Answer

Router R2 will summarize routes from area 0 into other areas.

Answer

Router R2 will create a static route for 10.0.0.0/22.

Answer

Router R2 will filter all routes not within 10.0.0.0/22.