# PE–PE Behavior Overview

PE 1 advertises the VPNv6 prefixes in the MP_REACH_NLRI attribute of the update messages sent to its MP-IBGP peer, PE 2. The AFI and SAFI values are negotiated for VPNv6. The AFI value is 2 for IPv6, and the SAFI value is 128 for MPLS-labeled VPN-IPv6.

When PE 2 receives the VPNv6 prefix 6001:0430::/48 with label L1, it imports the prefix into VRF B because VRF B’s import route target matches the route target received in the MP-BGP update. For all labeled VPNv6 prefixes installed in VRF B that come from the same endpoint on PE 1 (loopback FFFF::1.1.1.1/128), a single dynamic IPv6 interface stacked on top of an MPLS tunnel head is created in VRF B regardless of the number of different stacked labels associated with each VPNv6 prefix. The prefix is then installed in VRF B’s routing table as pointing to this dynamic IPv6 interface.

If PE 1 is not running either JunosE or Junos OS, each VPNv6 prefix usually has a different stacked label value sent in the MP-BGP update. If an implementation allocates one VPN interface per received stacked label, this behavior might potentially become a scaling issue if many dynamic IPv6 interfaces are allocated to resolve each VPNv6 prefix in VRF B.