Reference Guide

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 Dell Networking OS
The following sections describe how to implement BGP on 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 requires both IGP and BGP
convergence and can therefore be a lengthy process.
BGP add-path on Dell Networking OS 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.
Dell Networking OS supports 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
internal configured, BGP advertises the metric configured in the redistribute command as
MED.
• If BGP peer outbound route-map has metric configured, all other metrics are overwritten by this
configuration.
NOTE: When redistributing static, connected, or OSPF routes, there is no metric option. Simply
assign the appropriate route-map to the redistributed route.
The following table lists some examples of these rules.
Border Gateway Protocol IPv4 (BGPv4)
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