300-410 Infrastructure Services Practice Question
A network engineer is troubleshooting an MPLS L3VPN where customer routes are not being advertised between PE routers. The engineer verifies that the VRFs are configured correctly and that MPLS forwarding is operational. Which MP-BGP configuration is required to exchange VPNv4 routes between PE routers?
⚠ Common exam trap
The trap here is assuming that standard IPv4 BGP or just neighbor activation is sufficient, without configuring the specific VPNv4 address family.
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
✓
address-family vpnv4 unicast
To exchange VPNv4 routes between PE routers, MP-BGP must be configured with the address-family vpnv4 unicast. This address family carries the VPN-specific attributes, including route targets and the VPN label. Once activated, BGP can advertise and receive VPNv4 prefixes, allowing PEs to import routes into the correct VRFs. The other options are either for different address families or are supporting commands that do not by themselves enable VPNv4 route exchange.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
neighbor x.x.x.x activate
Why it's wrong here
The neighbor activate command is used within an address family to enable the exchange of routes for that address family with a specific neighbor. However, it must be configured under the correct address family, such as vpnv4 unicast. By itself, without specifying the vpnv4 address family, it does not enable VPNv4 route exchange. It is a necessary but not sufficient condition.
- ✗
address-family ipv4 unicast
Why it's wrong here
The address-family ipv4 unicast is used for standard IPv4 BGP routing, not for VPNv4. It does not carry the extended community attributes like route targets or the VPN label required for MPLS L3VPN. Configuring this alone would not enable the exchange of VPNv4 routes between PE routers, and customer routes would remain isolated.
- ✓
address-family vpnv4 unicast
Why this is correct
The address-family vpnv4 unicast configuration under BGP enables the exchange of VPNv4 routes between PE routers. This address family carries the VPN label and route targets, allowing PEs to import and export routes into VRFs. Without activating this address family, BGP will not advertise VPNv4 prefixes, and customer routes will not be propagated across the MPLS core.
- ✗
neighbor x.x.x.x send-community extended
Why it's wrong here
The send-community extended command is used to propagate extended BGP communities, which include route targets. While it is important for VPNv4 route exchange, it is not the configuration that enables the address family itself. Without the vpnv4 address family activated, extended communities alone will not allow VPNv4 routes to be exchanged. It is a supporting command, not the primary one.
Go deeper
Related to this question
Learn chapter
EIGRP Route Summarization and Filtering
Key term
MP-BGP for VPN
MP-BGP for VPN is an extension of the Border Gateway Protocol that carries multiple types of network layer information to enable scalable, isolated virtual private networks over a shared provider infrastructure.
Key term
MPLS Layer 3 VPN
A technology that uses Multiprotocol Label Switching to create secure, scalable virtual private networks that connect multiple sites at the network layer, where the service provider manages routing between customer sites.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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