MPLS and VPNs Flashcards

What is EVPN (Ethernet VPN) and what advantages does it have over VPLS?

Answer: EVPN uses MP-BGP to distribute MAC/IP routes, providing active-active multihoming, faster convergence, and integrated L2/L3 forwarding over MPLS or VXLAN

EVPN (RFC 7432) improves on VPLS by using BGP for MAC learning instead of data-plane flooding, enabling active-active multihoming, ARP suppression, integrated IRB routing, and operation over both MPLS and VXLAN overlays.

In Junos L3VPN, what is the purpose of the 'vrf-table-label' command?

Answer: Allocates a unique MPLS label per VRF routing table to enable MPLS-based forwarding for traffic arriving from the MPLS core toward CE devices

'vrf-table-label' in Junos allocates a per-VRF MPLS label that the egress PE uses to identify which VRF should receive incoming labeled traffic, enabling correct VPN traffic separation at the PE.

What is the 'inet.3' routing table used for in Junos MPLS?

Answer: Stores MPLS-resolved next-hops for BGP routes, allowing BGP to use MPLS LSPs as next-hops for traffic forwarding over the MPLS backbone

inet.3 contains MPLS tunnel next-hops (RSVP-TE LSPs and LDP LSPs). BGP references inet.3 to resolve next-hops through MPLS tunnels, allowing BGP routes to be forwarded using MPLS LSPs rather than direct IP routing.

What is the Junos command to verify an LDP-signaled MPLS LSP end-to-end?

Answer: ping mpls ldp fec [prefix/len] ttl 255

'ping mpls ldp fec [prefix/length]' sends MPLS ping probes along the LDP LSP for the specified FEC, verifying end-to-end LSP connectivity and data-plane forwarding.

What is 'inter-AS VPN' (Option B) in Junos L3VPN?

Answer: A method where ASBR routers exchange VPN routes using MP-eBGP, with each ASBR acting as a next-hop change point and allocating new MPLS labels for VPN routes crossing AS boundaries

Inter-AS VPN Option B (RFC 4364 section 10) uses ASBR-to-ASBR MP-eBGP to exchange labeled VPNv4 routes. Each ASBR changes the next-hop to itself and allocates new labels, enabling L3VPN across multiple autonomous systems without requiring LSPs that span ASes.

What is the role of the PE (Provider Edge) router in a Junos L3VPN deployment?

Answer: Maintains per-customer VRFs, connects to CE routers via routing protocols or static routes, and uses MP-BGP to distribute VPN routes with MPLS labels to other PEs

PE routers are the service provider edge devices that maintain per-customer VRF routing tables, exchange routing information with CE devices, and use MP-BGP with MPLS labels to interconnect customer sites across the service provider backbone.