300-410 BGP Troubleshooting Practice Test 4 — 15 Questions

Question 1

A network engineer runs the following command to troubleshoot a BGP Troubleshooting issue:

R1# show ip bgp vpnv4 vrf CUSTOMER 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
Route Distinguisher: 100:1 (default for vrf CUSTOMER)
*> 10.0.0.0/24      10.1.1.2                 0    100      0 65001 i
*> 192.168.1.0/24   10.1.1.2                 0    100      0 65001 i

Total number of prefixes 2

What does this output indicate?

Accepted Answer

The VRF CUSTOMER has two routes, both learned via BGP from AS 65001.. The show ip bgp vpnv4 vrf CUSTOMER routes command displays BGP VPNv4 routes for a specific VRF. The output shows two routes with route distinguisher 100:1, received from AS 65001. These are the routes available in the VRF CUSTOMER.

Answer

The VRF CUSTOMER is not receiving any routes because the RD is incorrect.

Answer

The VRF CUSTOMER has two routes, but they are not installed in the routing table.

Answer

The VRF CUSTOMER has two routes, but they are filtered by RT import policy.

Question 2

A network engineer runs the following command to troubleshoot a BGP Troubleshooting issue:

R1# debug ip bgp 10.1.1.2 updates
BGP: 10.1.1.2 sending UPDATE with 2 prefixes, 0 withdrawn
BGP: 10.1.1.2 sending UPDATE with 0 prefixes, 1 withdrawn

What does this output indicate?

Accepted Answer

The neighbor 10.1.1.2 is receiving two new routes and one route withdrawal.. The debug ip bgp updates with neighbor IP shows updates sent to the neighbor. The first line indicates an update with two prefixes advertised. The second line indicates an update with one prefix withdrawn. This is normal BGP operation.

Answer

The neighbor 10.1.1.2 is sending two new routes and one route withdrawal.

Answer

The BGP session with 10.1.1.2 is flapping.

Answer

The neighbor 10.1.1.2 is not reachable.

Question 3

A network engineer runs the following command to troubleshoot a BGP Troubleshooting issue:

R1# show bgp ipv4 unicast summary
BGP router identifier 1.1.1.1, local AS number 65000
BGP table version is 15, main routing table version 15
2 network entries using 288 bytes of memory
2 path entries using 160 bytes of memory
2/2 BGP path/bestpath attribute entries using 296 bytes of memory
1 BGP AS-PATH entries using 24 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
Bitfield cache entries: current 1 (at peak 1) using 32 bytes of memory
BGP using 800 total bytes of memory
BGP activity 6/0 prefixes, 6/0 paths, scan interval 60 secs

Neighbor        V           AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
10.1.1.2        4        65001      15      15       15    0    0 00:12:34        2
10.2.2.2        4        65002      10      12       15    0    0 00:08:21        0

What does this output indicate?

Accepted Answer

Neighbor 10.2.2.2 is not sending any routes, possibly due to filtering or no routes to advertise.. The show bgp summary output shows BGP neighbor states and prefix counts. Neighbor 10.1.1.2 is up and has sent 2 prefixes. Neighbor 10.2.2.2 is up but has sent 0 prefixes, indicating a possible issue with route advertisement or filtering.

Answer

Both neighbors are fully operational and exchanging routes.

Answer

Neighbor 10.1.1.2 is not sending any routes.

Answer

The BGP session with 10.2.2.2 is down.

Question 4

A network engineer runs the following command to troubleshoot a BGP Troubleshooting issue:

R1# show bgp ipv4 unicast 192.168.1.0/24
BGP routing table entry for 192.168.1.0/24, version 12
Paths: (1 available, best #1, table default)
  Advertised to update-groups:
     1          
  Refresh Epoch 1
  65001, (received & used)
    10.1.1.2 from 10.1.1.2 (10.1.1.2)
      Origin IGP, metric 0, localpref 100, valid, external, best
      Community: 100:200

What does this output indicate?

Accepted Answer

The prefix 192.168.1.0/24 has a community attribute of 100:200, which may affect routing decisions.. The show bgp output for a specific prefix shows one path with community 100:200 attached. The community is a BGP community value that can be used for route tagging and policy enforcement. The path is valid and best.

Answer

The prefix 192.168.1.0/24 is not installed in the routing table.

Answer

The prefix 192.168.1.0/24 is being filtered due to the community value.

Answer

The community 100:200 indicates the prefix is from a confederation.

Question 5

A network engineer runs the following command to troubleshoot a BGP Troubleshooting issue:

R1# show bgp ipv4 unicast 192.168.1.0/24
BGP routing table entry for 192.168.1.0/24, version 12
Paths: (2 available, best #2, table default)
  Advertised to update-groups:
     1          
  Refresh Epoch 1
  65001
    10.1.1.2 from 10.1.1.2 (10.1.1.2)
      Origin IGP, metric 0, localpref 100, valid, external
  Refresh Epoch 2
  65002
    10.2.2.2 from 10.2.2.2 (10.2.2.2)
      Origin IGP, metric 0, localpref 100, valid, external, best

What does this output indicate?

Accepted Answer

The path from AS 65002 is best due to a tie-breaking rule, such as lower neighbor router ID.. The output shows two paths with equal local preference and metric. The best path is from AS 65002, likely due to a tie-breaking rule such as lower router ID or older route. The path from AS 65001 is valid but not best.

Answer

Both paths are equally preferred, and BGP load-balances traffic.

Answer

The path from AS 65002 is best because it has a higher local preference.

Answer

The path from AS 65001 is best because it was received first.

Question 6

What is the default BGP keepalive timer value in Cisco IOS-XE?

Accepted Answer

60 seconds. The default BGP keepalive timer is 60 seconds, as defined in RFC 4271 and implemented in Cisco IOS-XE.

Answer

30 seconds

Answer

90 seconds

Answer

180 seconds

Question 7

Which BGP message type is used to advertise, withdraw, and update routes?

Accepted Answer

UPDATE. BGP UPDATE messages carry path attributes and NLRI for route advertisements and withdrawals.

Answer

OPEN

Answer

NOTIFICATION

Answer

KEEPALIVE

Question 8

What is the default BGP hold timer value in Cisco IOS-XE?

Accepted Answer

180 seconds. The default BGP hold timer is 180 seconds, as per RFC 4271 and Cisco IOS-XE defaults.

Answer

90 seconds

Answer

120 seconds

Answer

240 seconds

Question 9

Which BGP loop prevention mechanism relies on the AS_PATH attribute?

Accepted Answer

AS_PATH loop detection. BGP uses AS_PATH loop detection: a router rejects a route if its own AS number appears in the AS_PATH.

Answer

Split horizon

Answer

TTL expiration

Answer

Route poisoning

Question 10

What is the default BGP administrative distance for routes learned from an external peer (eBGP) in Cisco IOS-XE?

Accepted Answer

20. Cisco IOS-XE assigns eBGP routes an administrative distance of 20 by default.

Answer

200

Answer

110

Answer

120

Question 11

Which BGP attribute is used as the first tie-breaker in the route selection process when comparing routes from different peers?

Accepted Answer

WEIGHT. BGP selects the route with the highest WEIGHT (Cisco proprietary) first, then LOCAL_PREF.

Answer

LOCAL_PREF

Answer

AS_PATH length

Answer

MED

Question 12

What is the default behavior of BGP synchronization in Cisco IOS-XE?

Accepted Answer

Disabled by default. BGP synchronization is disabled by default in IOS-XE; routes can be advertised without being in the IGP.

Answer

Enabled by default

Answer

Enabled only for iBGP

Answer

Disabled only for eBGP

Question 13

Which BGP message type is sent when a fatal error is detected, causing the BGP session to close?

Accepted Answer

NOTIFICATION. NOTIFICATION messages are sent to report errors and terminate the BGP session.

Answer

OPEN

Answer

UPDATE

Answer

KEEPALIVE

Question 14

What is the default BGP update timer interval in Cisco IOS-XE?

Accepted Answer

30 seconds for eBGP, 0 seconds for iBGP. BGP does not have a fixed update timer like RIP; updates are triggered by changes, but the default minimum route advertisement interval (MRAI) is 30 seconds for eBGP and 0 seconds for iBGP.

Answer

60 seconds for both eBGP and iBGP

Answer

5 seconds for eBGP, 15 seconds for iBGP

Answer

0 seconds for eBGP, 30 seconds for iBGP

Question 15

Drag and drop the steps to establish an eBGP session between two IOS routers into the correct order, from first to last.

Accepted Answer

Configure BGP router ID under router bgp. The correct order starts with configuring the BGP router ID, then the local AS and neighbor remote AS, followed by specifying the neighbor update source, enabling the neighbor, and finally verifying the session.