Administrator Guide

advertises itself to another BGP speaker outside its local AS and when advertising routes within an AS. The
next hop attribute also serves as a way to direct traffic to another BGP speaker, rather than waiting for a
speaker to advertise.
The system allows you to set the next hop attribute in the CLI. Setting the next hop attribute lets you
determine a router as the next hop for a BGP neighbor.
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.
Border Gateway Protocol IPv4 (BGPv4) 207