Multiprotocol BGP
Multiprotocol extensions for BGP (MBGP) is defined in IETF RFC 2858. MBGP allows different types of
address families to be distributed in parallel.
MBGP allows information about the topology of the 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.
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.
Implement BGP with the Dell Networking OS
The following sections describe how to implement BGP on the Dell Networking OS.

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 situation requires both IGP
and BGP convergence and can be a lengthy process.
BGP add-path 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.
The Dell Networking OS version 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 with the route-map command, you can specify whether a peer
advertises the standard MED or uses the IGP cost as the MED.
When configuring this functionality:
• If the redistribute command does not have metric configured and the BGP peer outbound
route-map does have metric-type internal configured, BGP advertises the IGP cost as MED.
• If the redistribute command has metric configured (route-map set metric or
redistribute route-type metric) and the BGP peer outbound route-map has metric-type
186 Border Gateway Protocol IPv4 (BGPv4)