Lab 19 — 6PE — IPv6 over MPLS without P-Router IPv6

Active Nodes

Active routers: EDGE-1, EDGE-4, CORE-1, CORE-2, CE-CORP-1, CE-CORP-2

Key Concepts

6PE Architecture

6PE (IPv6 Provider Edge) carries IPv6 prefixes over an MPLS backbone without requiring IPv6 on P (core) routers. PE routers have dual-stack capability and use IPv4 LDP for label transport. IPv6 prefixes are encoded as labeled IPv6 routes in iBGP (address-family ipv6 with send-label). When an IPv6 packet arrives at a PE, it is encapsulated with a two-label stack: outer label for transport (IPv4 LDP toward remote PE) and inner label for the IPv6 prefix. P routers see only the outer IPv4 label and swap normally.

mpls ipv6 source-interface

The mpls ipv6 source-interface Loopback0 command tells the PE to use its IPv4 loopback address as the MPLS transport address for IPv6 label distribution. Without this, the router might try to use an IPv6 address for LDP transport, which P routers cannot reach. This is the critical configuration that enables 6PE over an IPv4-only MPLS backbone — the IPv6 routing uses IPv4 LDP sessions established between PE loopbacks.

BGP Labeled Unicast for IPv6

Under address-family ipv6 unicast, the send-label command enables exchange of labeled IPv6 routes. The label is used for the inner label in the 6PE stack. PE routers exchange IPv6 prefixes as VPNv6 (if using VRF) or as global IPv6 labeled-unicast. For 6PE (non-VRF), configure under global address-family ipv6 with send-label. The RR (CORE-1/2) must also be configured to reflect labeled IPv6 unicast routes between PE clients.

6PE Configuration

EDGE-16PE PE router — IPv6 labeled-unicast

mpls ipv6 source-interface Loopback0

router bgp 65000
 address-family ipv6 unicast
  neighbor 10.255.1.1 activate
  neighbor 10.255.1.1 send-community
  neighbor 10.255.1.1 send-label
  network 2001:db8:ff:2::1/128
  network 2001:db8:100:1::/64

interface Loopback0
 ip address 10.255.2.1 255.255.255.255
 ipv6 address 2001:db8:ff:2::1/128

CE-CORP-1CE with IPv6 LAN prefix

interface Loopback1
 ipv6 address 2001:db8:100:1::1/64

interface GigabitEthernet0/0
 ipv6 address 2001:db8:0:c100::c1/64

ipv6 route ::/0 2001:db8:0:c100::e1

Verification

show bgp ipv6 unicast

Expected: IPv6 prefixes from both CE sites in BGP table with labels. Next-hop shows IPv4-mapped PE loopback address.

show mpls forwarding-table

Expected: IPv6 prefixes (2001:db8::/32 range) in LFIB with label stack. Shows outer transport label + inner IPv6 label.

ping ipv6 2001:db8:100:2::1 source 2001:db8:100:1::1

Expected: CE-to-CE IPv6 ping success across MPLS backbone. P routers forward labeled packets without IPv6 routing table.

traceroute ipv6 2001:db8:100:2::1

Expected: Path shows PE loopbacks (IPv4) as intermediate hops — P routers not visible in traceroute (MPLS transparency).

Research and direction by Ioannis (John) Konstas; compiled and finalized with AI assistance.