Juniper JUNOSE 11.2.X BGP AND MPLS, Configuration Manual

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The BGP next hop that is advertised in the MP-BGP update includes the following:
•
A VPN-IPV6 address with the RD set to zero
•
The 16-byte IPv6 address encoded as an IPv4-mapped IPv6 address that contains the
IPv4 loopback address of the advertising PE router
The IPv4 IGP, such as OSPF, advertises the reachability of the loopback interfaces on
the PE routers. LDP binds label L2 to 1.1.1.1/32 on the P router.
CE–PE Behavior
CE 1 is connected to VRF A in PE 1 through an IPv4 interface. Similarly, CE 2 is connected
to VRF B in PE 2 through an IPv4 interface. You can alternatively run OSPF to the CE
devices over IPv6 links and redistribute the OSPF IPv6 routes into BGP.
The MP-BGP sessions between the CE devices and the VRFs in the PE routers are
established over TCPv4. The AFI value is 2, indicating IPv6; the SAFI value is 1, indicating
unicast. CE 1 advertises IPv6 network 6001:0430::/48 to its MP-BGP peer in VRF A. CE
2 advertises 6001:0431::/48 to its MP-BGP peer in VRF B. When it receives the advertised
prefix in VRF A, BGP adds 6001:0430::/48 to its BGP VPNv6 RIB with the stacked label
L1, which MPLS allocated for this prefix. The default IPv6 VRF label is L1.
PE–PE Behavior
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.
MPLS Data Plane Behavior
When PE 2 receives a data packet from CE 2 destined for the 6001:0430::/48 network,
the router detects a native IPv6 packet on its link to CE 2. PE 2 does a lookup in its VRF
B IPv6 routing table, prepends labels L2 and L1 to the IPv6 header, and then forwards
this packet on its core-facing IPv6 dynamic interface. When the P router receives this
packet, it performs a lookup on L2 and label switches the packet toward PE 1. The P
router either replaces L2 with another label or pops that label if PE 1 requested PHP.
Copyright © 2010, Juniper Networks, Inc. 400
JunosE 11.2.x BGP and MPLS Configuration Guide