Connecting Ipv6 Islands Across Multiple Ipv4 Domains; Figure 111: Ipv6 Tunneled Across Ipv4 Domains - Juniper BGP - CONFIGURATION GUIDE V 11.1.X Configuration Manual

Router CE 1 establishes an MP-BGP session over TCPv4 to PE 1 and advertises its
ability to reach the IPv6 network 2001:0430::/32. The MP-BGP update message
specifies an AFI value of 2 (IPv6) and a SAFI value of 1 (unicast). As the next hop in
the MP-REACH-NLRI attribute, CE 1 advertises the IPv6 address of the CE 1 interface
that links to PE 1.
Both IPv4 and IPv6 addresses must be configured on the PE-CE link. The IPv6 address
defaults to an IPv4-compatible address that can be overridden with policy.
PE 1 and PE 2 establish an MP-BGP session using their remote loopback IPv4
addresses as neighbor addresses. Router PE 1 installs in its IPv6 global routing table
the route advertised by CE 1. MP-BGP on PE 1 then binds a second-level label, L2,
and advertises the route to PE 2 with an AFI value of 2 (IPv6) and a SAFI value of 4
(labeled routes). The next hop that PE 1 advertises in the MP-REACH-NLRI attribute
is the IPv4 address of its loopback interface, 10.1.1.1, encoded in IPv6 format as
::10.1.1.1.
When MP-BGP on router PE 2 receives the advertisement, it associates the base
tunnel (to 10.1.1.0/24, label L1) with the next hop (::10.1.1.1) that was advertised
by PE 1 to reach the customer IPv6 island, 2001:0430::/32. Router PE 2 then uses
MP-BGP (AFI = 2, SAFI = 1) to advertise to CE 2 its ability to reach this network.
CE 2 sends native IPv6 packets destined for the 2001:0430::/32 network to PE 2. On
receipt, PE 2 performs a lookup in its global IPv6 routing table. PE 2 prepends two
labels to the IPv6 header (L1–L2–IPv6) and then forwards the packet out its core-facing
interface (10.2.2.2).
The P router does a lookup on L1 and label switches the packet toward PE 1. The P
router can either replace L1 with another label or pop L1 if PE 1 requested PHP.
When PE 1 receives the packet on its core-facing interface, it pops all the labels and
does a lookup in the global IPv6 routing table using the destination address in the
IPv6 header. PE 1 then forwards the native IPv6 packet out to CE 1 on the IPv6 link.

Connecting IPv6 Islands Across Multiple IPv4 Domains

When the IPv6 islands are separated by multiple IPv4 domains, the autonomous
system boundary routers between the IPv4 domains must be DS-BGP routers (Figure
111 on page 477).

Figure 111: IPv6 Tunneled Across IPv4 Domains

Each of these AS boundary routers establishes a peer relationship with the DS-BGP
routers in its own domain, creating a separate mesh of tunnels among the DS-BGP
Chapter 5: Configuring BGP-MPLS Applications
Connecting IPv6 Islands Across IPv4 Clouds with BGP
477