Question 744 of 2,152

MPLS L3VPN →mediumMultiple ChoiceObjective-mapped

send-community extended for VPNv4 PE Router Configuration

This 300-410 practice question tests your understanding of mpls l3vpn. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

A PE router has the following configuration:

router bgp 65000
 neighbor 10.0.0.1 remote-as 65000
 neighbor 10.0.0.1 update-source Loopback0

! address-family vpnv4

neighbor 10.0.0.1 activate
  neighbor 10.0.0.1 send-community extended

exit-address-family

What is wrong with this configuration?

A
The neighbor is missing the 'send-community extended' command under the VPNv4 address-family.
Incorrect. The configuration includes 'neighbor 10.0.0.1 send-community extended' under the VPNv4 address-family, so it is not missing.
B
The neighbor must be configured under the IPv4 unicast address-family first.
Why wrong: Incorrect. The neighbor does not need to be configured under the IPv4 unicast address-family first; activation under the VPNv4 address-family is sufficient for the session to exchange VPNv4 routes.
C
The update-source should be the interface facing the peer, not Loopback0.
Why wrong: Incorrect. In MPLS L3VPN, BGP sessions between PEs are typically established using loopback interfaces, so update-source Loopback0 is appropriate.
D
The neighbor remote-as should be different for VPNv4 sessions.
Why wrong: Incorrect. This is an iBGP session within the same autonomous system, so the remote-as must be the same AS number (65000).

Full breakdown with real-world context →

Quick Answer

The answer is that the configuration is missing the `neighbor 10.0.0.1 send-community extended` command under the VPNv4 address-family. For MPLS L3VPN, the `send-community extended` requirement is critical because VPNv4 routes carry route-target extended communities that control route import and export between VRFs; without this command, the PE router will advertise VPNv4 prefixes to its iBGP peer but strip the extended communities, rendering the routes unusable for VRF population. On the Cisco CCNP ENARSI 300-410 exam, this tests your understanding that activating a VPNv4 neighbor alone is insufficient—you must explicitly enable extended community propagation, a common trap where candidates assume `activate` implies community support. Remember the memory tip: "Activate the neighbor, then send the community—VPNv4 routes need their tags to travel."

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

The neighbor is missing the 'send-community extended' command under the VPNv4 address-family.

The configuration is correct. The 'neighbor 10.0.0.1 send-community extended' command is present under the VPNv4 address-family, which is required for carrying VPN routing information. Options B, C, and D are incorrect: the neighbor does not need to be configured under IPv4 unicast first, using Loopback0 as update-source is standard for iBGP sessions between PEs, and the remote-as is correctly set to the same AS for iBGP.

Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✓
The neighbor is missing the 'send-community extended' command under the VPNv4 address-family.
Why this is correct
Incorrect. The configuration includes 'neighbor 10.0.0.1 send-community extended' under the VPNv4 address-family, so it is not missing.
Related concept
OSPF neighbours must agree on key parameters.
✗
The neighbor must be configured under the IPv4 unicast address-family first.
Why it's wrong here
Incorrect. The neighbor does not need to be configured under the IPv4 unicast address-family first; activation under the VPNv4 address-family is sufficient for the session to exchange VPNv4 routes.
✗
The update-source should be the interface facing the peer, not Loopback0.
Why it's wrong here
Incorrect. In MPLS L3VPN, BGP sessions between PEs are typically established using loopback interfaces, so update-source Loopback0 is appropriate.
✗
The neighbor remote-as should be different for VPNv4 sessions.
Why it's wrong here
Incorrect. This is an iBGP session within the same autonomous system, so the remote-as must be the same AS number (65000).

Common exam traps

Common exam trap: OSPF can fail even when IP connectivity looks correct

OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.

Detailed technical explanation

How to think about this question

OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.

KKey Concepts to Remember

OSPF neighbours must agree on key parameters.
Router ID selection can affect neighbour relationships and LSDB output.
OSPF cost influences the preferred path.
A route can appear in OSPF information but not become the installed route.

TExam Day Tips

Check area mismatch first when OSPF adjacency fails.
Review passive interfaces when a network is advertised but no neighbour forms.
Use show ip ospf neighbor and show ip route clues carefully.

Key takeaway

OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.

Real-world example

How this comes up in practice

A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.

What to study next

Got this wrong? Here's your next step.

Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.

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FAQ

Questions learners often ask

What does this 300-410 question test?

MPLS L3VPN — This question tests MPLS L3VPN — OSPF neighbours must agree on key parameters..

What is the correct answer to this question?

The correct answer is: The neighbor is missing the 'send-community extended' command under the VPNv4 address-family. — The configuration is correct. The 'neighbor 10.0.0.1 send-community extended' command is present under the VPNv4 address-family, which is required for carrying VPN routing information. Options B, C, and D are incorrect: the neighbor does not need to be configured under IPv4 unicast first, using Loopback0 as update-source is standard for iBGP sessions between PEs, and the remote-as is correctly set to the same AS for iBGP.

What should I do if I get this 300-410 question wrong?

What is the key concept behind this question?

OSPF neighbours must agree on key parameters.

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