300-410 Layer 3 Technologies Practice Question
A network engineer is implementing MPLS Layer 3 VPN on a Cisco IOS XE router. The engineer wants to ensure that customer routes are advertised with the correct route distinguisher (RD) and route target (RT) extended communities. Which BGP address family must be configured to exchange VPNv4 routes between PE routers?
⚠ Common exam trap
Many candidates confuse the VRF address family, used for PE-CE routing, with the VPNv4 address family, used for PE-PE route exchange.
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
MPLS Layer 3 VPN uses BGP VPNv4 address family to exchange customer routes between PE routers. The VPNv4 address family carries the RD and RT extended communities that identify the VPN and control import/export. It must be activated on the PE-PE BGP session. The VRF address family is used for PE-CE routing and for assigning RDs and RTs, but not for exchanging VPNv4 routes.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
address-family ipv4 vrf CUSTOMER
Why it's wrong here
The address-family ipv4 vrf CUSTOMER is used to configure BGP for a specific VRF on the PE router. It is where customer routes are imported into BGP and where RDs and RTs are assigned. However, it does not exchange VPNv4 routes between PE routers. That requires the VPNv4 address family. This address family is for the PE-CE routing session, not the PE-PE session.
- ✗
address-family ipv4 multicast
Why it's wrong here
The address-family ipv4 multicast is used for multicast routing with BGP, such as for MVPN. It does not carry VPNv4 unicast routes and is not used for MPLS Layer 3 VPN unicast route exchange. This address family is relevant for multicast distribution trees and does not handle the RD and RT extended communities required for VPNv4 unicast.
- ✗
address-family ipv4 unicast
Why it's wrong here
The address-family ipv4 unicast is used for global IPv4 unicast routing, not for VPNv4. It does not carry RD or RT extended communities and cannot be used to exchange MPLS VPN routes between PE routers. While it may be used for the global routing table or for PE-CE sessions in some designs, it is not the correct address family for VPNv4 route exchange.
- ✓
address-family vpnv4 unicast
Why this is correct
The address-family vpnv4 unicast is used on PE routers to exchange VPNv4 routes with other PE routers. It carries the RD and RT extended communities along with the customer prefixes. This address family must be activated on the PE-PE BGP session to propagate MPLS VPN routing information. Without it, VPNv4 routes are not exchanged, and MPLS VPN connectivity fails.
Go deeper
Related to this question
Learn chapter
Device Management and Network Monitoring (SNMP, Syslog, NetFlow)
Key term
LDP Protocol
LDP, or Label Distribution Protocol, is a protocol that routers use to automatically exchange labels that enable MPLS (Multiprotocol Label Switching) to create fast, efficient paths for data packets across a network.
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.
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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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