300-410 BGP Troubleshooting Practice Test 2 — 15 Questions

Question 1

A network engineer runs the following command on Router R1:

R1# show bgp ipv4 unicast 10.4.4.0/24
BGP routing table entry for 10.4.4.0/24, version 8
Paths: (1 available, best #1, table default)
  Not advertised to any peer
  Refresh Epoch 1
  65006
    10.1.16.6 from 10.1.16.6 (10.6.6.6)
      Origin IGP, metric 0, localpref 100, valid, external, best
      rx pathid: 0, tx pathid: 0x0

Based on this output, what is the most likely reason the route is not advertised to any peer?

Accepted Answer

There is an outbound route-map or prefix-list filtering the route.. The route is valid and best, but not advertised. This could be due to outbound filtering (route-map, prefix-list) applied to the BGP neighbor, or the neighbor might not be configured to receive this prefix. Another possibility is that the route is suppressed by a policy.

Answer

The route has a local preference of 100, which is too low.

Answer

The BGP session to the neighbor is down.

Answer

The route is not in the routing table.

Question 2

A network engineer runs the following command on Router R1:

R1# show bgp neighbors 10.1.12.2 received-routes
BGP table version is 15, local router ID is 10.1.1.1
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
*> 10.2.2.0/24      10.1.12.2                0             0 65002 i

Total number of prefixes 1

Based on this output, what can be inferred about the BGP session?

Accepted Answer

The BGP session is established and the neighbor is advertising one prefix.. The output shows that R1 has received one prefix (10.2.2.0/24) from neighbor 10.1.12.2. The prefix is valid and best. This indicates the BGP session is established and exchanging routes.

Answer

The BGP session is not established.

Answer

The BGP session is in Active state.

Answer

The BGP session is in Idle state.

Question 3

A network engineer runs the following command on Router R1:

R1# show bgp ipv4 unicast 10.5.5.0/24
BGP routing table entry for 10.5.5.0/24, version 12
Paths: (1 available, best #1, table default)
  Advertised to update-groups:
     1
  Refresh Epoch 1
  65007
    10.1.17.7 from 10.1.17.7 (10.7.7.7)
      Origin IGP, metric 0, localpref 100, valid, external, best
      rx pathid: 0, tx pathid: 0x0

Based on this output, what does the 'r' in the status codes indicate if present? (Not shown here, but the engineer notices a similar route with 'r' status.)

Accepted Answer

The route is a RIB-failure, meaning it is not installed in the routing table because another route with a lower administrative distance exists.. The 'r' status code stands for RIB-failure, meaning the route is valid in BGP but not installed in the routing table because a route with a lower administrative distance (e.g., from OSPF or EIGRP) already exists.

Answer

The route is suppressed by a route-map.

Answer

The route is not valid due to next-hop unreachability.

Answer

The route is dampened.

Question 4

Given the following BGP configuration on router R1:

router bgp 65001
 bgp router-id 1.1.1.1
 neighbor 10.1.1.2 remote-as 65002
 neighbor 10.1.1.2 route-map SET-MED out
!
route-map SET-MED permit 10
 match ip address prefix-list LOOPBACKS
 set metric 100
!
route-map SET-MED permit 20
!
ip prefix-list LOOPBACKS permit 192.168.0.0/24

What is the effect of this configuration?

Accepted Answer

All routes are advertised to 10.1.1.2; the 192.168.0.0/24 route has MED 100, others have no MED.. The route-map SET-MED has two sequences. Sequence 10 matches prefix-list LOOPBACKS (192.168.0.0/24) and sets MED to 100. Sequence 20 permits everything else without setting MED, so other routes are advertised with their original MED.

Answer

Only the 192.168.0.0/24 route is advertised to 10.1.1.2, with MED 100.

Answer

All routes are advertised with MED 100 because the route-map is applied outbound.

Answer

Only the 192.168.0.0/24 route is advertised with no MED because the set metric is ignored.

Question 5

Consider the following BGP configuration on router R2:

router bgp 65002
 bgp router-id 2.2.2.2
 neighbor 10.2.2.1 remote-as 65001
 neighbor 10.2.2.1 route-map FILTER in
!
route-map FILTER deny 10
 match ip address prefix-list BLOCKED
!
route-map FILTER permit 20
!
ip prefix-list BLOCKED permit 10.0.0.0/8 le 32

Which statement is true about routes received from 10.2.2.1?

Accepted Answer

Routes with prefix 10.0.0.0/8 or more specific are denied; all others are permitted.. The route-map FILTER is applied inbound. Sequence 10 denies any route matching prefix-list BLOCKED (10.0.0.0/8 and more specific). Sequence 20 permits all other routes. Routes with 10.x.x.x are denied.

Answer

All routes are accepted because the deny statement is misconfigured.

Answer

Only routes exactly matching 10.0.0.0/8 are denied; other 10.x.x.x routes are permitted.

Answer

The route-map is applied outbound, so it affects routes sent to 10.2.2.1.

Question 6

Examine this BGP configuration on router R3:

router bgp 65003
 bgp router-id 3.3.3.3
 neighbor 10.3.3.2 remote-as 65002
 neighbor 10.3.3.2 ebgp-multihop 2
 neighbor 10.3.3.2 update-source Loopback0
!
interface Loopback0
 ip address 3.3.3.3 255.255.255.255

What is the likely issue with this configuration?

Accepted Answer

The neighbor 10.3.3.2 must be reachable via the loopback address 3.3.3.3; otherwise, the session will not come up.. The ebgp-multihop 2 allows the neighbor to be two hops away, but the update-source is set to Loopback0 (3.3.3.3). The neighbor 10.3.3.2 must be reachable via the loopback. If 10.3.3.2 is not reachable from 3.3.3.3, the session will not establish.

Answer

The ebgp-multihop value should be 1 for directly connected neighbors.

Answer

The remote-as 65002 should be the same as the local AS for eBGP.

Answer

The update-source command is not needed when using ebgp-multihop.

Question 7

A network engineer configures BGP on router R4:

router bgp 65004
 bgp router-id 4.4.4.4
 neighbor 10.4.4.3 remote-as 65003
 neighbor 10.4.4.3 password BGPsecret
!

What is the effect of the password command?

Accepted Answer

It enables MD5 authentication for the TCP session; the neighbor must also have the same password.. The password command enables MD5 authentication for the TCP connection between BGP peers. Both peers must have the same password; otherwise, the session will not establish.

Answer

It encrypts the BGP updates using the password as a key.

Answer

It sets a simple password that is sent in clear text with each BGP update.

Answer

It has no effect unless the neighbor is configured with the same password.

Question 8

Consider the following BGP configuration on router R5:

router bgp 65005
 bgp router-id 5.5.5.5
 neighbor 10.5.5.6 remote-as 65006
 neighbor 10.5.5.6 route-map SET-LP in
!
route-map SET-LP permit 10
 set local-preference 150
!

What is the result of this configuration?

Accepted Answer

All routes from 10.5.5.6 have their local preference set to 150, making them more preferred.. The route-map SET-LP is applied inbound. It sets the local preference to 150 for all routes received from 10.5.5.6. This makes those routes more preferred within the local AS compared to routes with default local preference (100).

Answer

Only routes that match a prefix-list are affected; otherwise, default local preference is used.

Answer

Local preference is set to 150 for routes sent to 10.5.5.6.

Answer

The route-map is ignored because local-preference can only be set outbound.

Question 9

Examine this BGP configuration on router R6:

router bgp 65006
 bgp router-id 6.6.6.6
 neighbor 10.6.6.7 remote-as 65007
 neighbor 10.6.6.7 weight 200
!

What is the effect of the weight command?

Accepted Answer

It sets the weight of all routes learned from 10.6.6.7 to 200, making them preferred over routes with lower weight.. The weight command assigns a weight value to routes from a specific neighbor. Weight is a Cisco-specific attribute that is local to the router. Higher weight is preferred over other routes. The default weight for eBGP routes is 0, so weight 200 makes routes from this neighbor preferred.

Answer

It sets the weight of routes sent to 10.6.6.7 to 200.

Answer

It has no effect because weight is only configurable under route-map.

Answer

It sets the MED value to 200 for routes from this neighbor.

Question 10

What is the default BGP keepalive interval and hold time for eBGP peers in Cisco IOS?

Accepted Answer

Keepalive 60 seconds, hold time 180 seconds. The default keepalive interval is 60 seconds, and the hold time is 180 seconds (three times the keepalive).

Answer

Keepalive 30 seconds, hold time 90 seconds

Answer

Keepalive 10 seconds, hold time 30 seconds

Answer

Keepalive 120 seconds, hold time 360 seconds

Question 11

Which BGP attribute is used for loop prevention in eBGP?

Accepted Answer

AS_PATH. The AS_PATH attribute contains the list of AS numbers a route has traversed. If a BGP router receives a route with its own AS number in the AS_PATH, it discards the route to prevent loops.

Answer

NEXT_HOP

Answer

LOCAL_PREF

Answer

MED

Question 12

In BGP, what is the default administrative distance for eBGP routes?

Accepted Answer

20. The default administrative distance for eBGP is 20, while for iBGP it is 200. This means eBGP routes are more trusted than iBGP routes.

Answer

200

Answer

120

Answer

110

Question 13

Which TWO commands would a network engineer use to verify the BGP next-hop reachability issue when a route is not being installed in the routing table? (Choose TWO.)

Accepted Answer

show ip bgp. The show ip bgp command displays the BGP table with status codes; if the next hop is not reachable, the route will show as 'r' (RIB-failure) or not be installed. The show ip route command verifies if the next-hop IP is present in the routing table. show ip bgp neighbors displays neighbor state but not next-hop reachability. show ip bgp summary shows neighbor summary, not route details. debug ip bgp updates is a debug command, not a verification command.

Answer

show ip bgp neighbors

Answer

show ip bgp summary

Answer

debug ip bgp updates

Question 14

Which TWO statements about BGP route reflectors are true when troubleshooting route propagation issues? (Choose TWO.)

Accepted Answer

A route reflector forwards routes received from a non-client peer to all client and non-client peers.. Route reflectors pass routes from non-client peers to all other peers (including other clients and non-clients) without requiring full mesh, but they do not modify the AS_PATH. The cluster ID is used to prevent loops within a cluster. Option B is incorrect because route reflectors do not prepend the AS_PATH. Option D is incorrect because clients must peer only with the route reflector, not with each other. Option E is incorrect because the next-hop is not changed by default.

Answer

A route reflector appends its own AS number to the AS_PATH when reflecting routes.

Answer

Clients in a route reflector cluster must be fully meshed with each other.

Answer

A route reflector changes the next-hop attribute to its own address when reflecting routes.

Question 15

Which THREE symptoms indicate a BGP route dampening issue that is causing routes to be suppressed? (Choose THREE.)

Accepted Answer

The show ip bgp command displays the route with a 'd' status code.. Route dampening suppresses routes that flap frequently. Symptoms include routes showing as 'dampened' in the BGP table, routes being absent from the routing table despite being in the BGP table, and the show ip bgp dampened-paths command listing those routes. Option A is incorrect because dampening does not affect the neighbor state. Option E is incorrect because the prefix-list is not directly related to dampening.

Answer

The BGP neighbor state flaps between Established and Idle.

Answer

The show ip prefix-list command indicates that routes are being filtered.