MPLS L3VPN practice questions

A network engineer is troubleshooting an MPLS L3VPN where CE1 (192.168.1.0/24) cannot reach CE2 (192.168.2.0/24). The PE routers are running OSPF with the CEs. On PE1, the VRF configuration includes route-target import and export 100:100. The show ip vrf detail command on PE1 shows the VRF is active, but the CE1 loopback is not present in the VRF routing table. The show ip route vrf CUSTOMER command on PE1 shows only directly connected interfaces. What is the most likely cause?

Trap 1: The route-target import on PE1 is misconfigured.

Incorrect because route-target import/export is for VPNv4 route exchange between PEs, not for CE-PE route learning.

Trap 2: The CE1 interface is not in the VRF.

Incorrect because the VRF shows active and directly connected routes, meaning the interface is assigned to the VRF.

Trap 3: The MP-BGP session between PE1 and PE2 is down.

Incorrect because the issue is local CE route learning, not VPNv4 route exchange.

A
The route-target import on PE1 is misconfigured.
Why wrong: Incorrect because route-target import/export is for VPNv4 route exchange between PEs, not for CE-PE route learning.
B
The OSPF process on PE1 is not configured under the VRF.
Correct: OSPF must be configured with 'router ospf <pid> vrf CUSTOMER' to populate the VRF routing table.
C
The CE1 interface is not in the VRF.
Why wrong: Incorrect because the VRF shows active and directly connected routes, meaning the interface is assigned to the VRF.
D
The MP-BGP session between PE1 and PE2 is down.
Why wrong: Incorrect because the issue is local CE route learning, not VPNv4 route exchange.

Question 2hardmultiple choice

An engineer is troubleshooting an MPLS L3VPN where CE1 (10.1.1.0/24) cannot reach CE2 (10.2.2.0/24). The PE routers have MP-BGP peering and the VRF is configured with route-target import 100:100. On PE1, the show ip bgp vpnv4 vrf CUSTOMER command shows the route for 10.2.2.0/24 with a next-hop of 192.168.1.2 (the PE2 loopback), but the show ip route vrf CUSTOMER command does not have this route. The show mpls forwarding-table on PE1 does not show a label for 192.168.1.2. What is the most likely cause?

Trap 1: The VRF route-target import is missing on PE2.

Incorrect because the route is received on PE1, so import is working.

Trap 2: The MP-BGP session is not using the loopback interface.

Incorrect because the route shows a next-hop of the loopback, indicating the session is using it.

Trap 3: The VRF on PE1 has the wrong route-target export.

Incorrect because the issue is with route installation, not export.

A
The VRF route-target import is missing on PE2.
Why wrong: Incorrect because the route is received on PE1, so import is working.
B
LDP is not enabled on the core-facing interfaces of PE1 or the P routers.
Correct: Without LDP, there is no label for the BGP next-hop, preventing route installation.
C
The MP-BGP session is not using the loopback interface.
Why wrong: Incorrect because the route shows a next-hop of the loopback, indicating the session is using it.
D
The VRF on PE1 has the wrong route-target export.
Why wrong: Incorrect because the issue is with route installation, not export.

Question 3hardmultiple choice

A network engineer is troubleshooting an MPLS L3VPN where CE1 (10.1.1.0/24) cannot reach CE2 (10.2.2.0/24). The PE routers are using OSPF with the CEs and MP-BGP between them. On PE1, the show ip bgp vpnv4 vrf CUSTOMER command shows the route for 10.2.2.0/24 with a next-hop of 192.168.1.2, and the show ip route vrf CUSTOMER command shows the route as well. However, traffic from CE1 to CE2 fails. The show ip cef vrf CUSTOMER 10.2.2.0 command on PE1 shows the next-hop as 192.168.1.2 but the output interface is 'no route'. What is the most likely cause?

Trap 1: The OSPF process on PE1 is not redistributing connected routes.

Incorrect because the IGP route to the PE2 loopback is missing, not the CE routes.

Trap 2: The VRF route-target import is misconfigured.

Incorrect because the route is present in the VRF routing table.

Trap 3: MPLS is not enabled on the core-facing interfaces.

Incorrect because the issue is IGP reachability, not MPLS label switching.

A
The OSPF process on PE1 is not redistributing connected routes.
Why wrong: Incorrect because the IGP route to the PE2 loopback is missing, not the CE routes.
B
The PE2 loopback is not advertised into the IGP (OSPF/IS-IS) of the service provider core.
Correct: The BGP next-hop must be reachable via IGP for CEF to resolve the output interface.
C
The VRF route-target import is misconfigured.
Why wrong: Incorrect because the route is present in the VRF routing table.
D
MPLS is not enabled on the core-facing interfaces.
Why wrong: Incorrect because the issue is IGP reachability, not MPLS label switching.

Question 4hardmultiple choice

An engineer is troubleshooting an MPLS L3VPN where CE1 (10.1.1.0/24) cannot reach CE2 (10.2.2.0/24). The PE routers have MP-BGP peering and the VRF is configured with route-target import 100:100. On PE1, the show ip bgp vpnv4 vrf CUSTOMER command shows the route for 10.2.2.0/24 with a next-hop of 192.168.1.2, but the show ip route vrf CUSTOMER command does not have this route. The show ip bgp vpnv4 all 10.2.2.0/24 command on PE1 shows the route is received but not best. What is the most likely cause?

Trap 1: The route-target import on PE1 is missing.

Incorrect because the route is received, so import is working.

Trap 2: The VRF on PE1 has a different route-target export.

Incorrect because the route is received, indicating export is correct.

Trap 3: The MP-BGP session is using an incorrect address family.

Incorrect because the route is received in the VPNv4 address family.

A
The route-target import on PE1 is missing.
Why wrong: Incorrect because the route is received, so import is working.
B
The BGP next-hop (PE2 loopback) is not reachable in the global routing table.
Correct: BGP requires the next-hop to be reachable for the route to be considered best and installed.
C
The VRF on PE1 has a different route-target export.
Why wrong: Incorrect because the route is received, indicating export is correct.
D
The MP-BGP session is using an incorrect address family.
Why wrong: Incorrect because the route is received in the VPNv4 address family.

Question 5hardmultiple choice

A network engineer is troubleshooting an MPLS L3VPN where CE1 (10.1.1.0/24) cannot reach CE2 (10.2.2.0/24). The PE routers are using eBGP with the CEs. On PE1, the show ip bgp vpnv4 vrf CUSTOMER command shows the route for 10.2.2.0/24 with a next-hop of 192.168.1.2, and the show ip route vrf CUSTOMER command shows the route. However, traffic from CE1 to CE2 fails. The show ip cef vrf CUSTOMER 10.2.2.0 command on PE1 shows the next-hop as 192.168.1.2 and the output interface as GigabitEthernet0/0. The show mpls forwarding-table 192.168.1.2 detail command on PE1 shows a label but the outgoing interface is 'aggregate'. What is the most likely cause?

Trap 1: LDP is not enabled on the core-facing interfaces.

Incorrect because a label is present, so LDP is working.

Trap 2: The VRF route-target import is misconfigured.

Incorrect because the route is installed in the VRF.

Trap 3: The MP-BGP session is using the wrong update-source.

Incorrect because the route is received and installed.

A
The PE2 loopback address is accidentally configured on PE1.
Correct: If PE1 has the same loopback IP, it will treat itself as the egress for that prefix, causing 'aggregate' in the LFIB.
B
LDP is not enabled on the core-facing interfaces.
Why wrong: Incorrect because a label is present, so LDP is working.
C
The VRF route-target import is misconfigured.
Why wrong: Incorrect because the route is installed in the VRF.
D
The MP-BGP session is using the wrong update-source.
Why wrong: Incorrect because the route is received and installed.

Question 6mediummultiple choice

An engineer is troubleshooting an MPLS L3VPN where CE1 (10.1.1.0/24) cannot reach CE2 (10.2.2.0/24). The PE routers are using OSPF with the CEs. On PE1, the show ip bgp vpnv4 vrf CUSTOMER command shows the route for 10.2.2.0/24 with a next-hop of 192.168.1.2, and the show ip route vrf CUSTOMER command shows the route. However, traffic from CE1 to CE2 fails. The show ip cef vrf CUSTOMER 10.2.2.0 command on PE1 shows the next-hop as 192.168.1.2 and the output interface as GigabitEthernet0/0. The show ip route 192.168.1.2 command on PE1 shows the route with a next-hop of 10.0.0.2 and output interface GigabitEthernet0/0. The show mpls forwarding-table 192.168.1.2 detail command on PE1 shows a label with outgoing interface GigabitEthernet0/0. What is the most likely cause?

Trap 1: The VRF route-target import on PE1 is misconfigured.

Incorrect because the route is installed in the VRF.

Trap 2: The OSPF process on PE1 is not redistributing BGP routes into OSPF.

Incorrect because the route is in the VRF routing table, and OSPF redistribution is for CE-PE, not for forwarding.

Trap 3: The MP-BGP session is not using the loopback interface.

Incorrect because the route is received and installed.

A
The VRF route-target import on PE1 is misconfigured.
Why wrong: Incorrect because the route is installed in the VRF.
B
The CE1 router does not have a default route or specific route to 10.2.2.0/24.
Correct: If CE1 does not have a route to the remote prefix, it will drop traffic or send it to a default gateway that may not exist.
C
The OSPF process on PE1 is not redistributing BGP routes into OSPF.
Why wrong: Incorrect because the route is in the VRF routing table, and OSPF redistribution is for CE-PE, not for forwarding.
D
The MP-BGP session is not using the loopback interface.
Why wrong: Incorrect because the route is received and installed.

Question 7hardmultiple choice

A network engineer is troubleshooting an MPLS L3VPN where CE1 (10.1.1.0/24) cannot reach CE2 (10.2.2.0/24). The PE routers are using eBGP with the CEs. On PE1, the show ip bgp vpnv4 vrf CUSTOMER command shows the route for 10.2.2.0/24 with a next-hop of 192.168.1.2, and the show ip route vrf CUSTOMER command shows the route. However, traffic from CE1 to CE2 fails. The show ip bgp vpnv4 vrf CUSTOMER 10.2.2.0/24 command on PE1 shows the route is received and best, but the show ip bgp vpnv4 vrf CUSTOMER 10.2.2.0/24 neighbors 192.168.1.2 advertised-routes command on PE2 shows the route is not advertised. What is the most likely cause?

Trap 1: The MP-BGP session between PE1 and PE2 is down.

Incorrect because the route is received on PE1, so the session is up.

Trap 2: The route-target export on PE2 is misconfigured.

Incorrect because the route is received, so export is working.

Trap 3: The VRF on PE1 has the wrong route-target import.

Incorrect because the route is received on PE1.

A
The VRF on PE2 does not have the CE2 route in its routing table.
Correct: If the route is not in the VRF routing table on PE2, it cannot be advertised via BGP.
B
The MP-BGP session between PE1 and PE2 is down.
Why wrong: Incorrect because the route is received on PE1, so the session is up.
C
The route-target export on PE2 is misconfigured.
Why wrong: Incorrect because the route is received, so export is working.
D
The VRF on PE1 has the wrong route-target import.
Why wrong: Incorrect because the route is received on PE1.

Question 8mediummultiple choice

An engineer is troubleshooting an MPLS L3VPN where CE1 (10.1.1.0/24) cannot reach CE2 (10.2.2.0/24). The PE routers are using OSPF with the CEs. On PE1, the show ip bgp vpnv4 vrf CUSTOMER command shows the route for 10.2.2.0/24 with a next-hop of 192.168.1.2, and the show ip route vrf CUSTOMER command shows the route. However, traffic from CE1 to CE2 fails. The show ip cef vrf CUSTOMER 10.2.2.0 command on PE1 shows the next-hop as 192.168.1.2 and the output interface as GigabitEthernet0/0. The show mpls forwarding-table 192.168.1.2 detail command on PE1 shows a label with outgoing interface GigabitEthernet0/0. The show ip route 192.168.1.2 command on PE1 shows the route with a next-hop of 10.0.0.2 and output interface GigabitEthernet0/0. The show ip cef 192.168.1.2 command on PE1 shows the next-hop as 10.0.0.2 and output interface GigabitEthernet0/0. What is the most likely cause?

Trap 1: The VRF route-target import on PE2 is misconfigured.

Incorrect because the route is installed on PE1, and import is for receiving routes.

Trap 2: The OSPF process on PE1 is not redistributing BGP routes into OSPF.

Incorrect because the route is in the VRF, and OSPF redistribution is for CE-PE, not for forwarding.

Trap 3: The MP-BGP session is using an incorrect update-source.

Incorrect because the route is received and installed.

A
The VRF route-target import on PE2 is misconfigured.
Why wrong: Incorrect because the route is installed on PE1, and import is for receiving routes.
B
The PE2 router does not have a label for the CE1 prefix in its LFIB.
Correct: If PE2 cannot forward return traffic due to missing label, traffic will be dropped.
C
The OSPF process on PE1 is not redistributing BGP routes into OSPF.
Why wrong: Incorrect because the route is in the VRF, and OSPF redistribution is for CE-PE, not for forwarding.
D
The MP-BGP session is using an incorrect update-source.
Why wrong: Incorrect because the route is received and installed.

Question 9hardmultiple choice

A network engineer is troubleshooting an MPLS L3VPN where CE1 (10.1.1.0/24) cannot reach CE2 (10.2.2.0/24). The PE routers are using eBGP with the CEs. On PE1, the show ip bgp vpnv4 vrf CUSTOMER command shows the route for 10.2.2.0/24 with a next-hop of 192.168.1.2, and the show ip route vrf CUSTOMER command shows the route. However, traffic from CE1 to CE2 fails. The show ip bgp vpnv4 vrf CUSTOMER 10.2.2.0/24 command on PE1 shows the route is received and best, but the show ip bgp vpnv4 vrf CUSTOMER 10.2.2.0/24 command on PE1 also shows the route has the 'r' flag (RIB-failure). What is the most likely cause?

Trap 1: The route-target import on PE1 is misconfigured.

Incorrect because the route is received, so import is working.

Trap 2: The MP-BGP session is not using the loopback interface.

Incorrect because the route is received and best.

Trap 3: The VRF on PE1 has a different route-target export.

Incorrect because the route is received, indicating export is correct.

A
There is a static route in the VRF for 10.2.2.0/24 with a lower administrative distance.
Correct: A static route or IGP route with lower AD will prevent the BGP route from being installed.
B
The route-target import on PE1 is misconfigured.
Why wrong: Incorrect because the route is received, so import is working.
C
The MP-BGP session is not using the loopback interface.
Why wrong: Incorrect because the route is received and best.
D
The VRF on PE1 has a different route-target export.
Why wrong: Incorrect because the route is received, indicating export is correct.

Question 10mediummultiple choice

A network engineer runs the following command on Router PE1:

PE1# show mpls forwarding-table 192.168.1.0 24

Local Outgoing Prefix Bytes Label Outgoing Next Hop Label Label or Tunnel Id Switched interface 16 Pop Label 192.168.1.0/24 0 Gi0/0 10.1.1.2 17 22 192.168.1.0/24 0 Gi0/1 10.2.2.2

Based on this output, which statement is correct?

Trap 1: The router has a routing loop for prefix 192.168.1.0/24.

No evidence of loop; both paths are valid.

Trap 2: Penultimate Hop Popping is disabled on this router.

The first entry shows 'Pop Label', which indicates PHP is enabled.

Trap 3: The prefix 192.168.1.0/24 is learned via BGP from two different…

The output does not show the routing protocol; it only shows MPLS forwarding entries.

A
The router is performing load balancing across two LSPs for prefix 192.168.1.0/24.
Two forwarding entries for the same prefix with different outgoing interfaces and labels indicate ECMP load balancing.
B
The router has a routing loop for prefix 192.168.1.0/24.
Why wrong: No evidence of loop; both paths are valid.
C
Penultimate Hop Popping is disabled on this router.
Why wrong: The first entry shows 'Pop Label', which indicates PHP is enabled.
D
The prefix 192.168.1.0/24 is learned via BGP from two different neighbors.
Why wrong: The output does not show the routing protocol; it only shows MPLS forwarding entries.

Question 11mediummultiple choice

A network engineer runs the following command on Router PE2:

PE2# show ip bgp vpnv4 vrf CUSTOMER_A 10.10.10.0 24

BGP routing table entry for 10.10.10.0/24, version 15 Paths: (1 available, best #1, table CUSTOMER_A) Advertised to update-groups: 1 Refresh Epoch 1 Local, imported path from 10.10.10.0/24

10.1.1.1 (metric 20) from 10.1.1.1 (10.1.1.1)

Origin incomplete, metric 0, localpref 100, valid, internal, best Extended Community: RT:100:100 mpls labels in/out 18/19

Based on this output, what is the problem?

Trap 1: The route is not being advertised to any BGP peer.

The output shows 'Advertised to update-groups: 1', meaning it is being advertised.

Trap 2: The route is missing the required Route Target community.

The output shows 'Extended Community: RT:100:100', so the RT is present.

Trap 3: The route has an incorrect label binding.

Labels 18/19 are present and valid; no error is shown.

A
The route is not being advertised to any BGP peer.
Why wrong: The output shows 'Advertised to update-groups: 1', meaning it is being advertised.
B
The route is missing the required Route Target community.
Why wrong: The output shows 'Extended Community: RT:100:100', so the RT is present.
C
The route is functioning correctly with no issues.
All fields indicate a valid, best route with labels and RT.
D
The route has an incorrect label binding.
Why wrong: Labels 18/19 are present and valid; no error is shown.

Question 12mediummultiple choice

A network engineer runs the following command on Router P1:

P1# show mpls ldp neighbor

Peer LDP Ident: 10.0.0.2:0, Local LDP Ident: 10.0.0.1:0 TCP connection: 10.0.0.2.646 - 10.0.0.1.48632 State: Oper, Msgs sent/rcvd: 120/118, Downstream Up time: 00:12:34 LDP discovery sources: GigabitEthernet0/0, Src IP addr: 10.1.1.2 Addresses bound to peer LDP Ident:

10.0.0.2         192.168.1.1

Based on this output, which statement is correct?

Trap 1: The LDP session is down.

The state is 'Oper', meaning operational.

Trap 2: The router is not receiving label bindings from the neighbor.

The output does not show label bindings, but the session is up; bindings may be exchanged.

Trap 3: The LDP router ID is misconfigured.

The local and peer LDP Identifiers are consistent and no error is indicated.

A
The LDP session is down.
Why wrong: The state is 'Oper', meaning operational.
B
The LDP session is up and functioning correctly.
All indicators show a normal, operational LDP session.
C
The router is not receiving label bindings from the neighbor.
Why wrong: The output does not show label bindings, but the session is up; bindings may be exchanged.
D
The LDP router ID is misconfigured.
Why wrong: The local and peer LDP Identifiers are consistent and no error is indicated.

Question 13mediummultiple choice

A network engineer runs the following command on Router CE1:

CE1# show ip route vrf CUSTOMER_B 10.20.20.0 24

Routing Table: CUSTOMER_B Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2 i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2 ia - IS-IS inter area, * - candidate default, U - per-user static route o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

10.0.0.0/24 is subnetted, 1 subnets
B       10.20.20.0 [20/0] via 10.1.1.2, 00:02:34

Based on this output, what is the problem?

Trap 1: The route is not being installed in the routing table.

The route is present with 'B' code, indicating it is installed.

Trap 2: The VRF is not configured correctly.

The VRF name appears in the output, and the route is present.

Trap 3: The next hop is unreachable.

The output does not show any indication of unreachability; the route is active.

A
The route is not being installed in the routing table.
Why wrong: The route is present with 'B' code, indicating it is installed.
B
The route is functioning correctly.
All fields indicate a valid BGP route.
C
The VRF is not configured correctly.
Why wrong: The VRF name appears in the output, and the route is present.
D
The next hop is unreachable.
Why wrong: The output does not show any indication of unreachability; the route is active.

Question 14easymultiple choice

A network engineer runs the following command on Router PE3:

PE3# show ip vrf interfaces
Interface      IP-Address      VRF                              Protocol

Gi0/0 10.1.1.1 CUSTOMER_C up Gi0/1 10.2.2.1 CUSTOMER_D up

Based on this output, which statement is correct?

Trap 1: Interface Gi0/0 is down.

The 'Protocol' column shows 'up' for both interfaces.

Trap 2: VRF CUSTOMER_C has no routes.

The output only shows interface assignment; it does not show routing information.

Trap 3: The router has no VRF configuration.

Two VRFs are shown, so VRF configuration exists.

A
Both interfaces are correctly assigned to VRFs and are operational.
The output shows both interfaces are up and assigned to VRFs.
B
Interface Gi0/0 is down.
Why wrong: The 'Protocol' column shows 'up' for both interfaces.
C
VRF CUSTOMER_C has no routes.
Why wrong: The output only shows interface assignment; it does not show routing information.
D
The router has no VRF configuration.
Why wrong: Two VRFs are shown, so VRF configuration exists.

Question 15hardmultiple choice

A network engineer runs the following command on Router PE4:

PE4# show bgp vpnv4 unicast all summary

BGP router identifier 10.0.0.4, local AS number 65001 BGP table version is 25, main routing table version 25 5 network prefixes using 640 bytes of memory 5 path entries using 400 bytes of memory 3/3 BGP path/bestpath attribute entries using 360 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 BGP using 1424 total bytes of memory BGP activity 15/10 prefixes, 20/15 paths, scan interval 60 secs

Neighbor        V           AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
10.0.0.5        4        65001    1020    1015       25    0    0 00:12:34        5
10.0.0.6        4        65002     500     495       25    0    0 00:06:20        0

Based on this output, what is the problem?

Trap 1: Neighbor 10.0.0.5 is not exchanging prefixes.

It has received 5 prefixes, so exchange is happening.

Trap 2: Both neighbors are in the Idle state.

Both show an Up/Down time, so they are established.

Trap 3: The BGP table is empty.

The output shows 5 network prefixes, so the table is not empty.

A
Neighbor 10.0.0.5 is not exchanging prefixes.
Why wrong: It has received 5 prefixes, so exchange is happening.
B
Neighbor 10.0.0.6 is not sending any prefixes.
The 'State/PfxRcd' column shows 0 for 10.0.0.6, indicating no prefixes received.
C
Both neighbors are in the Idle state.
Why wrong: Both show an Up/Down time, so they are established.
D
The BGP table is empty.
Why wrong: The output shows 5 network prefixes, so the table is not empty.

Question 16easymultiple choice

A network engineer runs the following command on Router PE5:

PE5# show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
10.0.0.7          1   FULL/DR        00:00:32    10.1.1.7        GigabitEthernet0/0
10.0.0.8          1   FULL/BDR       00:00:35    10.2.2.8        GigabitEthernet0/1

Based on this output, which statement is correct?

Trap 1: One neighbor is in the EXSTART state.

Both are in FULL state.

Trap 2: The router is not the DR for any segment.

The output shows the router's neighbors as DR and BDR; the router itself could be DROTHER, but that is not indicated.

Trap 3: There is a mismatch in OSPF area IDs.

No area mismatch is indicated; adjacencies are up.

A
Both OSPF adjacencies are fully established.
The state is FULL for both neighbors, indicating full adjacency.
B
One neighbor is in the EXSTART state.
Why wrong: Both are in FULL state.
C
The router is not the DR for any segment.
Why wrong: The output shows the router's neighbors as DR and BDR; the router itself could be DROTHER, but that is not indicated.
D
There is a mismatch in OSPF area IDs.
Why wrong: No area mismatch is indicated; adjacencies are up.

Question 17hardmultiple choice

A network engineer runs the following command on Router PE6:

PE6# show mpls forwarding-table

Local Outgoing Prefix Bytes Label Outgoing Next Hop Label Label or Tunnel Id Switched interface 16 Pop Label 10.0.0.1/32 0 Gi0/0 10.1.1.1 17 20 10.0.0.2/32 0 Gi0/1 10.2.2.2 18 Untagged 10.0.0.3/32 0 Gi0/2 10.3.3.3

Based on this output, what is the problem?

Trap 1: The router has run out of local labels.

Local labels 16, 17, 18 are assigned, so labels are available.

Trap 2: Penultimate Hop Popping is misconfigured.

PHP is correctly shown for the first entry; the issue is specific to the third entry.

Trap 3: The prefix 10.0.0.3/32 is not reachable.

The entry exists, so the prefix is reachable; the problem is with MPLS encapsulation.

A
MPLS is not enabled on interface Gi0/2.
The 'Untagged' label indicates MPLS is not enabled on the outgoing interface or the next hop is not an MPLS router.
B
The router has run out of local labels.
Why wrong: Local labels 16, 17, 18 are assigned, so labels are available.
C
Penultimate Hop Popping is misconfigured.
Why wrong: PHP is correctly shown for the first entry; the issue is specific to the third entry.
D
The prefix 10.0.0.3/32 is not reachable.
Why wrong: The entry exists, so the prefix is reachable; the problem is with MPLS encapsulation.

Question 18mediummultiple choice

A network engineer runs the following command on Router PE7:

PE7# show bgp vpnv4 unicast vrf CUSTOMER_E labels

Network Next Hop In Label/Out Label

10.10.10.0/24    10.0.0.8            18/22
   10.20.20.0/24    10.0.0.9            19/23

Based on this output, which statement is correct?

Trap 1: The router is not receiving labels from its BGP peers.

Out labels are present (22 and 23), so labels are received.

Trap 2: The VRF CUSTOMER_E has no routes.

Two routes are shown, so the VRF has routes.

Trap 3: The label allocation is failing.

Labels are allocated and displayed correctly.

A
The router is correctly assigning labels for VPNv4 routes.
Both entries have valid incoming and outgoing labels.
B
The router is not receiving labels from its BGP peers.
Why wrong: Out labels are present (22 and 23), so labels are received.
C
The VRF CUSTOMER_E has no routes.
Why wrong: Two routes are shown, so the VRF has routes.
D
The label allocation is failing.
Why wrong: Labels are allocated and displayed correctly.

Question 19mediummultiple choice

Examine the following partial configuration on a PE router:

interface GigabitEthernet0/1
 ip vrf forwarding CUSTOMER-A
 ip address 10.1.1.1 255.255.255.252

router bgp 65000
 neighbor 192.168.1.1 remote-as 65000
 neighbor 192.168.1.1 update-source Loopback0

! address-family ipv4 vrf CUSTOMER-A

neighbor 10.1.1.2 remote-as 65001
  neighbor 10.1.1.2 activate

exit-address-family

What is the effect of this configuration?

Trap 1: The BGP session will fail because the neighbor must be configured…

For VRF peers, the neighbor must be configured under the VRF address-family, not the global BGP process. This is correct.

Trap 2: The BGP session will fail because the neighbor remote-as must match…

The CE router is in a different AS (65001), so eBGP is appropriate. The remote-as must match the CE's AS, which is 65001.

Trap 3: The BGP session will fail because the update-source is not…

The update-source is only needed for the iBGP session to the route reflector; the VRF neighbor uses the interface IP by default, which is correct.

A
The eBGP session between PE and CE will be established successfully.
The VRF is defined, the interface is in the VRF, and the BGP neighbor is correctly configured under the VRF address-family. The neighbor IP is on the same subnet, so the eBGP session should come up.
B
The BGP session will fail because the neighbor must be configured under the global BGP process.
Why wrong: For VRF peers, the neighbor must be configured under the VRF address-family, not the global BGP process. This is correct.
C
The BGP session will fail because the neighbor remote-as must match the AS of the PE router.
Why wrong: The CE router is in a different AS (65001), so eBGP is appropriate. The remote-as must match the CE's AS, which is 65001.
D
The BGP session will fail because the update-source is not specified for the VRF neighbor.
Why wrong: The update-source is only needed for the iBGP session to the route reflector; the VRF neighbor uses the interface IP by default, which is correct.

Question 20mediummultiple choice

Consider the following configuration on a PE router:

ip vrf CUSTOMER-B

rd 100:1 route-target export 100:1 route-target import 100:2 !

interface GigabitEthernet0/2
 ip vrf forwarding CUSTOMER-B
 ip address 192.168.2.1 255.255.255.252

What is the effect of this configuration?

Trap 1: The PE will export routes with RT 100:2 and import routes with RT…

This reverses the export and import RTs, which is not what is configured.

Trap 2: The VRF will not work because the RD and RT must be identical.

RD and RT are independent; they can be different. RD is used to make routes unique, RT controls import/export.

Trap 3: The VRF will not work because route-target import and export must…

Route-targets are configured under the VRF definition, not under BGP. This is the correct place.

A
The PE will export routes from VRF CUSTOMER-B with RT 100:1 and import routes with RT 100:2.
The route-target export sets the RT on exported VPNv4 routes; the route-target import filters incoming VPNv4 routes to only those with RT 100:2.
B
The PE will export routes with RT 100:2 and import routes with RT 100:1.
Why wrong: This reverses the export and import RTs, which is not what is configured.
C
The VRF will not work because the RD and RT must be identical.
Why wrong: RD and RT are independent; they can be different. RD is used to make routes unique, RT controls import/export.
D
The VRF will not work because route-target import and export must be configured under the BGP VRF address-family.
Why wrong: Route-targets are configured under the VRF definition, not under BGP. This is the correct place.