BGP Troubleshooting

A network engineer is troubleshooting a BGP peering issue between two directly connected routers, R1 and R2. R1 is configured with 'neighbor 10.1.1.2 remote-as 65002' and 'neighbor 10.1.1.2 update-source Loopback0', while R2 uses 'neighbor 10.1.1.1 remote-as 65001' and 'neighbor 10.1.1.1 update-source Loopback0'. The loopback interfaces are not advertised into any IGP, and there is no static route for the loopback addresses. The BGP session remains in Idle state. What is the most likely cause?

An engineer is troubleshooting a missing BGP route on R3. R3 has an eBGP session with R4 (AS 65004) and an iBGP session with R1 (AS 65003). R4 advertises a prefix 192.168.1.0/24 to R3, and R3's BGP table shows the route with next-hop 10.1.4.4. However, R3 does not install this route in its routing table. The output of 'show ip bgp 192.168.1.0/24' on R3 shows the route as valid but not best. What is the most likely cause?

A network engineer is troubleshooting a BGP route advertisement issue. Router R1 in AS 65001 is configured to redistribute connected routes into BGP. The route 10.10.10.0/24 is learned via BGP on R2 (AS 65002), but R2's iBGP neighbor R3 (AS 65002) does not receive this route. R2 and R3 have a full iBGP mesh, and the BGP session is established. The output of 'show ip bgp' on R2 shows the route with the 'r' flag (RIB-failure). What is the most likely cause?

An engineer is troubleshooting a BGP peering problem between two routers, R1 (AS 65001) and R2 (AS 65002), connected via a firewall. The BGP session is flapping every few seconds. The engineer notices that the TCP connection is established, but BGP OPEN messages are not exchanged. The firewall logs show that TCP port 179 is allowed, but packets with the BGP marker (0xFFFFFFFF) are being dropped. What is the most likely cause?

A network engineer is troubleshooting missing BGP routes on R3. R1 (AS 65001) is an eBGP peer of R2 (AS 65002), and R2 is an iBGP peer of R3 (AS 65002). R1 advertises the prefix 172.16.1.0/24 to R2. On R2, 'show ip bgp' shows the prefix with next-hop 10.1.1.1 (R1's interface). R3's BGP table does not contain this prefix. R2 and R3 are not route reflectors, and there are no other iBGP peers. What is the most likely cause?

An engineer is troubleshooting a BGP route selection issue. Router R1 receives two paths for prefix 10.0.0.0/8: one from eBGP peer R2 (AS 65002) with weight 0, local preference 100, and AS path 65002; and another from eBGP peer R3 (AS 65003) with weight 0, local preference 200, and AS path 65003 65004. R1's BGP table shows the path from R3 as the best route. The engineer wants the path from R2 to be preferred. What should the engineer do?

A network engineer is troubleshooting a BGP route advertisement issue. Router R1 (AS 65001) has an eBGP session with R2 (AS 65002). R1 is advertising the prefix 192.168.1.0/24 to R2. On R2, the route appears in the BGP table but is not installed in the routing table. The output of 'show ip bgp 192.168.1.0/24' on R2 shows the route as valid, best, but with the 'r' flag (RIB-failure). The routing table on R2 shows a static route for 192.168.1.0/24 with administrative distance 1. What is the most likely cause?

An engineer is troubleshooting a BGP peering issue between two routers, R1 and R2, connected via a serial link. The BGP session is established, but routes are not being exchanged. The engineer checks the BGP configuration and sees that both routers have the 'neighbor' commands correctly configured. The output of 'show ip bgp summary' shows the session is in the Established state, but the prefix counts are zero. What is the most likely cause?

A network engineer is troubleshooting a BGP route advertisement issue. Router R1 (AS 65001) is an eBGP peer of R2 (AS 65002). R1 is advertising the prefix 10.0.0.0/8 to R2. R2 has an iBGP session with R3 (AS 65002). R3's BGP table shows the prefix 10.0.0.0/8 with next-hop 10.1.1.1 (R1's interface). However, R3 does not install this route in its routing table. The output of 'show ip route 10.0.0.0' on R3 shows no route. The engineer checks the routing table on R3 and sees that the interface connected to 10.1.1.0/24 is down. What is the most likely cause?

A network engineer runs the following command on Router R1: R1# show bgp summary BGP router identifier 10.1.1.1, local AS number 65001 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 2/1 BGP path/bestpath attribute entries using 288 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 BGP using 736 total bytes of memory BGP activity 4/2 prefixes, 4/2 paths, scan interval 60 secs Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 10.1.12.2 4 65002 1023 1047 15 0 0 00:12:34 0 192.168.1.2 4 65003 0 0 0 0 0 never Active Based on this output, what is the problem with the BGP session to 192.168.1.2?

A network engineer runs the following command on Router R1: R1# show bgp ipv4 unicast 10.1.1.0/24 BGP routing table entry for 10.1.1.0/24, version 2 Paths: (1 available, best #1, table default) Advertised to update-groups: 1 Refresh Epoch 1 Local 10.1.1.1 from 0.0.0.0 (10.1.1.1) Origin IGP, metric 0, localpref 100, weight 32768, valid, sourced, best rx pathid: 0, tx pathid: 0x0 Based on this output, which statement is correct?

A network engineer runs the following command on Router R1: R1# show ip bgp neighbors 10.1.12.2 BGP neighbor is 10.1.12.2, remote AS 65002, external link BGP version 4, remote router ID 10.2.2.2 BGP state = Idle Last read 00:00:00, last write 00:00:00, hold time is 180, keepalive interval is 60 seconds Neighbor sessions: 1 active, is not multisession capable (disabled) Neighbor capabilities: Route refresh: advertised and received(new) Four-octets ASN Capability: advertised and received Address family IPv4 Unicast: advertised and received Enhanced Refresh Capability: advertised Multisession Capability: State is never active Message statistics: InQ depth is 0 OutQ depth is 0 Based on this output, what is the most likely cause of the BGP session being in Idle state?

A network engineer runs the following command on Router R1: R1# show bgp ipv4 unicast 10.2.2.0/24 BGP routing table entry for 10.2.2.0/24, version 5 Paths: (1 available, best #1, table default) Not advertised to any peer Refresh Epoch 1 65002 10.1.12.2 from 10.1.12.2 (10.2.2.2) Origin IGP, metric 0, localpref 100, valid, external, best rx pathid: 0, tx pathid: 0x0 Based on this output, what is a potential issue with this route?

A network engineer runs the following command on Router R1: R1# show bgp ipv4 unicast 10.3.3.0/24 BGP routing table entry for 10.3.3.0/24, version 10 Paths: (2 available, best #2, table default) Advertised to update-groups: 1 Refresh Epoch 1 65003 65004 10.1.13.3 from 10.1.13.3 (10.3.3.3) Origin IGP, metric 0, localpref 100, valid, external rx pathid: 0, tx pathid: 0 Refresh Epoch 1 65005 10.1.15.5 from 10.1.15.5 (10.5.5.5) Origin IGP, metric 0, localpref 200, valid, external, best rx pathid: 0, tx pathid: 0x0 Based on this output, why is the path via 10.1.15.5 chosen as best?

A network engineer runs the following command on Router R1: R1# show bgp neighbors 10.1.12.2 advertised-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 *> 10.1.1.0/24 0.0.0.0 0 32768 i *> 10.2.2.0/24 10.1.12.2 0 0 65002 i Total number of prefixes 2 Based on this output, what can be concluded about the route 10.2.2.0/24?

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?

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?

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.)

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?

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?

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?

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?

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?

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?

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

Which BGP attribute is used for loop prevention in eBGP?

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

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.)

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

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

Which TWO configuration steps are required to troubleshoot and fix a BGP route that is not being advertised to an EBGP neighbor due to the next-hop-self issue? (Choose TWO.)

Which THREE conditions must be met for a BGP route to be considered the best path and installed in the routing table? (Choose THREE.)

A large enterprise network is experiencing intermittent loss of reachability to a set of prefixes originated by R2. R1 (AS 65001) and R2 (AS 65002) are eBGP peers. R1 has the following relevant configuration: router bgp 65001, neighbor 10.1.1.2 remote-as 65002, neighbor 10.1.1.2 route-map RM_IN in. The route-map RM_IN has a clause: match ip address prefix-list PL_ALLOW, set local-preference 200. The prefix-list PL_ALLOW permits 10.0.0.0/8 le 24. R2 advertises 10.0.0.0/8 and more specific prefixes including 10.1.0.0/16. R1 shows: BGP table has 10.0.0.0/8 with local-pref 200, but 10.1.0.0/16 is missing. What is the root cause?

A network engineer redistributes OSPF routes into BGP on router R1. R1 has: router bgp 65001, redistribute ospf 1 route-map RM_OSPF. The route-map RM_OSPF sets metric 100. OSPF routes from area 0 are redistributed, but routes from area 1 are missing in BGP. R1 shows: show ip ospf database shows area 1 routes as inter-area (IA). What is the root cause?

R1 and R2 are iBGP peers in AS 65001. R1 has: neighbor 10.1.1.2 route-reflector-client. R2 advertises a prefix 192.168.1.0/24 with next-hop 10.1.1.2. R3, another iBGP speaker not a client of R1, receives the prefix but the next-hop is unchanged (10.1.1.2) and R3 cannot reach it because 10.1.1.2 is not directly connected. R1 has no other configuration. What is the root cause?

R1 and R2 are eBGP peers. R1 advertises a summary route 10.0.0.0/8 via aggregate-address 10.0.0.0 255.0.0.0 summary-only. R2 receives the summary but also expects to receive more specific routes (e.g., 10.1.0.0/16) for traffic engineering. R2's BGP table shows only the summary, and the more specific routes are missing. R1's configuration includes: router bgp 65001, network 10.1.0.0 mask 255.255.0.0, and aggregate-address 10.0.0.0 255.0.0.0 summary-only. What is the root cause?

R1 and R2 are iBGP peers. R1 has: neighbor 10.1.1.2 route-map RM_SET in. The route-map RM_SET sets community 100:100. R2 advertises a prefix 172.16.1.0/24 with community 200:200. R1 receives the prefix and the community is changed to 100:100. However, R1's BGP table shows the prefix with community 100:100, but R1 does not propagate this prefix to its other iBGP peer R3. R3 has no special configuration. What is the root cause?

R1 and R2 are eBGP peers. R1 advertises a prefix 192.168.1.0/24 with MED 50. R2 also receives the same prefix from another eBGP peer R3 with MED 100. R2's BGP best path selection chooses the path via R1 because of lower MED. However, R2's routing table shows the next-hop for 192.168.1.0/24 as 10.1.1.1 (R1), but R2 cannot ping 192.168.1.1. R2 has: interface GigabitEthernet0/0, ip address 10.1.1.2 255.255.255.0, and no ip route to 192.168.1.0/24 other than BGP. R1's interface to R2 has ip address 10.1.1.1 255.255.255.0. R1's BGP table shows the prefix with next-hop 10.1.1.1 (self). What is the root cause?

R1 and R2 are iBGP peers in AS 65001. R1 has: neighbor 10.1.1.2 route-reflector-client. R2 advertises a prefix 10.0.0.0/8 with a community of no-export. R1 reflects this prefix to its other client R3. R3 is in a different AS (65002) via eBGP. R3 receives the prefix but does not advertise it to its eBGP neighbor R4 in AS 65003. What is the root cause?

R1 and R2 are eBGP peers. R1 advertises a prefix 172.16.1.0/24 with AS_PATH 65001 65002. R2 receives the prefix and its BGP table shows AS_PATH 65001 65002. R2 has a route-map applied inbound that sets local-preference 150 for routes with AS_PATH containing 65002. R2 also has another eBGP peer R3 that advertises the same prefix with AS_PATH 65001 65003. R2's BGP best path selection chooses the path via R3 because of shorter AS_PATH length (2 vs 3). However, the network engineer expects the path via R1 to be preferred due to the higher local-preference. What is the root cause?

R1 and R2 are iBGP peers in AS 65001. R1 has: neighbor 10.1.1.2 next-hop-self. R2 advertises a prefix 10.0.0.0/8 with next-hop 10.1.1.2. R1 receives the prefix and changes the next-hop to 10.1.1.1 (its own IP) due to next-hop-self. R1 then advertises this prefix to its eBGP peer R3 in AS 65002. R3 receives the prefix with next-hop 10.1.1.1. R3 has a static route to 10.1.1.0/24 via its interface to R1. However, R3 cannot reach 10.0.0.0/8 because R1 does not have a route to 10.0.0.0/8 in its routing table. What is the root cause?

A network engineer runs the following command to troubleshoot a BGP Troubleshooting issue: R1# debug ip bgp updates BGP(0): 10.1.1.2 UPDATE rcvd w/ attr: nexthop 10.1.1.2, origin i, localpref 100, metric 0 BGP(0): 10.1.1.2 rcvd 192.168.1.0/24 BGP(0): 10.1.1.2 rcvd UPDATE w/ attr: nexthop 10.1.1.2, origin i, localpref 100, metric 0 BGP(0): 10.1.1.2 rcvd 192.168.2.0/24 BGP(0): 10.1.1.2 rcvd UPDATE w/ attr: nexthop 10.1.1.2, origin i, localpref 100, metric 0 -- unreachable BGP(0): 10.1.1.2 rcvd 192.168.3.0/24 What does this output indicate?

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, best Refresh Epoch 2 65002 10.2.2.2 from 10.2.2.2 (10.2.2.2) Origin IGP, metric 0, localpref 50, valid, external What does this output indicate?

A network engineer runs the following command to troubleshoot a BGP Troubleshooting issue: R1# show bgp neighbors 10.1.1.2 advertised-routes BGP table version is 14, 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 *> 10.0.0.0/24 0.0.0.0 0 32768 i *> 192.168.1.0/24 0.0.0.0 0 32768 i Total number of prefixes 2 What does this output indicate?

A network engineer runs the following command to troubleshoot a BGP Troubleshooting issue: R1# show bgp neighbors 10.1.1.2 received-routes BGP table version is 14, 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 *> 10.0.0.0/24 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?

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?

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?

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?

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?

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?

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

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

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

Which BGP loop prevention mechanism relies on the AS_PATH attribute?

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

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

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

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

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

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

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

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

Which TWO statements correctly describe the behavior of BGP conditional route injection? (Choose TWO.)

An engineer is troubleshooting a BGP route advertisement issue. Which TWO commands can be used to verify whether a prefix is being advertised to a specific BGP neighbor? (Choose TWO.)

Which TWO actions will prevent a BGP route from being installed in the routing table (RIB) while still being present in the BGP table? (Choose TWO.)

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

An engineer is troubleshooting BGP convergence issues. Which THREE commands can be used to verify BGP path selection and best path criteria? (Choose THREE.)

An engineer configures a route reflector cluster with two route reflectors in the same cluster ID. After convergence, some iBGP routes are missing on clients, and 'show ip bgp' shows the path with 'r' flag. What is the most likely explanation?

A network engineer configures BGP synchronization on an iBGP router. The IGP (OSPF) does not carry the BGP routes. Unexpectedly, the router does not advertise these iBGP routes to eBGP neighbors. What is the most likely explanation?

An engineer configures AS path prepending on an eBGP route to influence inbound traffic. However, traffic from a specific iBGP neighbor still prefers the prepended path. What is the most likely explanation?

An engineer configures mutual redistribution between OSPF and EIGRP without route tagging. After convergence, some routes oscillate between the two protocols. What is the most likely explanation?

An engineer configures a DMVPN Phase 2 network. Spoke-to-spoke tunnels are established, but traffic between spokes is not using the direct tunnel. What is the most likely explanation?

An engineer configures IPsec with a transform set that includes ESP-SHA-HMAC and ESP-AES-256. The VPN tunnel fails to establish, and debug shows 'transform set mismatch'. What is the most likely explanation?

An engineer configures Control Plane Policing (CoPP) with a policy that denies all traffic in class-default. After applying the policy, BGP sessions to the router fail. What is the most likely explanation?

An engineer enables unicast RPF (uRPF) in strict mode on an interface. Afterward, some legitimate traffic from a BGP neighbor is dropped. The neighbor has two paths to the router, and traffic may arrive on a different interface than the return path. What is the most likely explanation?

An engineer configures OSPF on a link with an MTU of 1500 on one side and 1400 on the other. The OSPF neighbor state is stuck in EXSTART. What is the most likely explanation?