Operation of 6VPE

The operation of MPLS VPN for IPv6 or 6VPE is similar to the operation of MPLS VPN for IPv4. 6VPE has the following key features:

■ It has an MPLS core network running an IPv4 routing protocol (IGP) and a label distribution protocol (LDP or RSVP for TE).

■ The edge LSRs or PE routers are capable of running IPv6.

■ The edge LSRs or PE routers have VRFs that designate the VPNs toward the customer or CE routers.

■ A full mesh of MP-iBGP sessions exists between the edge LSRs or PE routers and serves to distribute the IPv6 VPN prefixes and their associated labels. (These IPv6 VPN prefixes are now called vpnv6 prefixes.) This is also known as vpnv6 + label. The label encoding is done according to RFC 3107.

■ The IPv6 packets are transported across the MPLS network with two labels: an IGP label as the top label and a BGP (or VPN) label as the bottom label.

■ The PE and CE routers have an IPv6 routing protocol between them.

As you can see, these are similar key features to the ones for MPLS VPN for IPv4. The difference, of course, is that now the transported protocol is IPv6 and not IPv4. Notice that the PE routers must run IPv4 and IPv6 and that the P routers must not be capable of IPv6. Figure 9-8 shows the basic operation of the 6VPE solution.

Figure 9-8 6VPE Network

VPN Red

VPN Red eBGP or Static eBGP or Static

IPv4 IGP, eBGP or Static

Full Mesh Of MP-iBGP

IPv4 IGP, eBGP or Static eBGP or Static eBGP or Static

eBGP or Static

eBGP or Static

VPN Blue

VPN Blue

The 6VPE and MPLS VPN for IPv4 solutions are different in the following ways:

■ Address family vpnv6 is used instead of address family vpnv4 for BGP; there is vpnv6 + label instead of vpnv4 + label between the PE routers.

■ The next hop of the vpnv6 prefix is an IPv4-mapped IPv6 address of the egress PE.

A vpnv6 prefix is an IPv6 prefix that is prepended with a 64-bit route distinguisher (RD). This combination of an IPv6 prefix and RD makes the vpnv6 prefix unique throughout the network, allowing overlapping IPv6 prefix ranges in different VPNs, as long as those VPNs are not allowed to communicate with each other.

You can use 6VPE and MPLS VPN for IPv4 at the same time, even on the same interface on the PE router toward the CE router. You can have both an IPv6 VRF and an IPv4 VRF configured on the same interface.

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