Information Technology Reference
In-Depth Information
MP-BGP for IPv6 Deployment Considerations
The mechanisms and techniques provided by BGPv4 are also available in MP-BGP for
handling IPv6 NLRI. The decision process, scalability mechanisms, and policy features are
not specific to IPv4 NLRI; they apply quite well to IPv6 NLRI. This means that route
reflection, route dampening, BGP confederations, Multi-Exit Discriminator (MED), and
outbound route filtering (just to name a few) are all unchanged for MP-BGP.
In general, BGP is protocol-agnostic. It runs on top of TCP, which is the same in IPv4 and
IPv6. This means that the underlying network layer protocol can be either IPv4 or IPv6
without requiring any changes to BGP. However, two fields in BGP messages are IPv4-
specific—router ID and cluster ID. Both are 4 bytes long.
The BGP Open message contains a field for the router ID. This field is 4 bytes long. There
is no particular requirement that this address be reachable or even an actual IPv4 address,
only that it be a unique 32-bit number.
The router generates the router ID automatically based on IPv4 addressing configured on
the router, the address configured on the loopback interface, or, if there is no loopback, the
highest IPv4 address on any of the interfaces.
In a pure IPv6 deployment, no IPv4 addressing is configured, providing nothing for the
router to use in building a router ID. In this case, the router ID must be manually configured
under the BGP process. If there is no router ID, BGP sessions do not form.
The other component of BGP that requires a unique 4-byte number is the cluster ID, used
on route reflectors. The cluster ID is carried with the NLRI in the BGP UPDATE messages.
If a router ID is configured, this value is used for the cluster ID. The cluster ID can also be
configured independent of the router ID. The originator ID attribute is also a 4-byte value
that is used with route reflection. The manual configuration of a 4-byte router ID provides
the value for the originator ID.
The concept of autosummarization along classful boundaries does not exist in IPv6.
Because IPv6 does not use address classes, the
auto-summary
command in BGP has
no effect on IPv6 prefix information.
Configuring MP-BGP for IPv6
The BGP configuration for IPv4 and IPv6 is very similar. However, when you configure
IPv6, the address family-style (AF-style) configuration is required. The AF-style configu-
ration is used for all address families besides IPv4.
IPv6 forwarding is not enabled by default. This must be done explicitly in global configu-
ration mode with the command
ipv6 unicast-routing
. Do this before configuring IPv6
routing.
