Reference Guide

Border Gateway Protocol IPv4 (BGPv4) | 191

Multiprotocol BGP

MBGP for IPv6 unicast is supported on platforms e c

MBGP for IPv4 Multicast is supported on platform c e

Multiprotocol Extensions for BGP (MBGP) is defined in IETF RFC 2858. MBGP allows different types of

address families to be distributed in parallel. This allows information about the topology of IP

Multicast-capable routers to be exchanged separately from the topology of normal IPv4 and IPv6 unicast

routers. It allows a multicast routing topology different from the unicast routing topology.

Implementing BGP with FTOS

Additional Path (Add-Path) support

The Add-path feature reduces convergence times by advertising multiple paths to its peers for the same

address prefix without replacing existing paths with new ones. By default, a BGP speaker advertises only

the best path to its peers for a given address prefix. If the best path becomes unavailable, the BGP speaker

withdraws its path from its local RIB and recalculates a new best path. This requires both IGP and BGP

convergence and can therefore be a lengthy process.

BGP add-path on FTOS reduces the time taken for BGP convergence by advertising multiple paths to its

peers for the same address prefix without new paths implicitly replacing the existing paths. An iBGP

speaker that receives multiple paths from its peers should calculate the best path in its own. BGP add-path

helps switchover to next new best path based on IGP convergence time when best path becomes

unavailable.

Advertise IGP cost as MED for redistributed routes

When using multipath connectivity to an external AS, you can advertise the MED value selectively to each

peer for redistributed routes. For some peers you can set the internal/IGP cost as the MED while setting

others to a constant pre-defined metric as MED value.

FTOS 8.3.1.0 and later support configuring the

set metric-type internal command in a route-map to

advertise the IGP cost as the MED to outbound EBGP peers when redistributing routes. The configured

set

metric

value overwrites the default IGP cost.

By using the

redistribute command in conjunction with the route-map command, you can specify whether

a peer advertises the standard MED or uses the IGP cost as the MED.

Note: It is possible to configure BGP peers that exchange both unicast and multicast network layer

reachability information (NLRI), but you cannot connect Multiprotocol BGP with BGP. Therefore, you

cannot redistribute Multiprotocol BGP routes into BGP.