Information Technology Reference
In-Depth Information
BGP4 Multiprotocol Extensions (MP-BGP) for IPv6
RFC 2545 specifies the use of BGP attributes for passing on IPv6 route information. MP-
BGP is also referred as BGP4+. The MP_REACH_NLRI (multiprotocol-reachable) attrib-
ute describes reachable destinations. It includes the next-hop address and a list of
Network Layer Reachability Information (NLRI) prefixes of reachable networks. The
MP_UNREACH_NLRI (multiprotocol-unreachable) attribute conveys unreachable net-
works. IOS currently supports these BGP4 multiprotocol attributes to communicate
reachability information for IPv6 networks.
Models
This section describes transition mechanisms and deployment models to migrate from
IPv4 to IPv6. During a transition time, both protocols can coexist in the network. The
three major transition mechanisms are
Dual-stack (IPv4 and IPv6 coexist in hosts and networks.)
■
Key
To p i c
Tunneling (IP v6 packets are enc ap s ulated into IP v4 packets.)
■
Tran slat ion (IP v6 packets are t ran slated to IP v4 packets.)
■
IPv6 deployment models are also divided into three major categories:
Dual-stack model (IPv4 and IPv6 coexist on hosts and network.)
■
Hybrid model (combination of Intra-Site Automatic Tunneling Protocol (ISATAP) or
manually configured tunnels and dual-stack mechanisms)
■
Service block model (combination of ISATAP and manually configured tunnels and
dual-stack mechanisms)
■
Each model provides several advantages and disadvantages; familiarize yourself with
those. Of all these models, the dual-stack model is recommended because it requires no
tunneling and is easier to manage.
Dual-Stack Mechanism
Devices running dual-stack can communicate with both IPv4 and IPv6 devices. The IPv4
protocol stack is used between IPv4 hosts, and the IPv6 protocol stack is used between
IPv6 hosts. The application decides which stack to use to communicate with destination
hosts. As shown in Figure 9-10, when a frame is received, the Ethernet type code identifies
whether the packet needs to be forwarded to IPv4 (0x0800) or IPv6 (ox86DD). When us-
ing dual stacks, a host also uses DNS to determine which stack to use to reach a destina-
tion. If DNS returns an IPv6 (AAAA record) address to the host, the host uses the IPv6
stack. If DNS returns an IPv4 (A record) address to the host, the host uses the IPv4 stack.
IPv6 over IPv4 Tunnels
nels. With tunneling, IPv6 traffic is encapsulated within IPv4 packets so that they are sent
