Multiprotocol BGPMultiprotocol extensions for BGP (MBGP) is defined in IETF RFC 2858. MBGP allows different types ofaddress families to be distributed in parallel.MBGP allows information about the topology of the IP multicast-capable routers to be exchangedseparately from the topology of normal IPv4 and IPv6 unicast routers. It allows a multicast routingtopology different from the unicast routing topology.MBGP uses either an IPv4 address configured on the interface (which is used to establish the IPv6session) or a stable IPv4 address that is available in the box as the next-hop address. As a result, whileadvertising an IPv6 network, exchange of IPv4 routes does not lead to martian next-hop message logs.NOTE: It is possible to configure BGP peers that exchange both unicast and multicast network layerreachability information (NLRI), but you cannot connect multiprotocol BGP with BGP. Therefore,you cannot redistribute multiprotocol BGP routes into BGP.Implement BGP with Dell Networking OSThe following sections describe how to implement BGP on Dell Networking OS.Additional Path (Add-Path) SupportThe add-path feature reduces convergence times by advertising multiple paths to its peers for the sameaddress prefix without replacing existing paths with new ones. By default, a BGP speaker advertises onlythe best path to its peers for a given address prefix. If the best path becomes unavailable, the BGP speakerwithdraws its path from its local RIB and recalculates a new best path. This situation requires both IGPand BGP convergence and can be a lengthy process. BGP add-path also helps switchover to the nextnew best path when the current best path is unavailable.Advertise IGP Cost as MED for Redistributed RoutesWhen using multipath connectivity to an external AS, you can advertise the MED value selectively to eachpeer for redistributed routes. For some peers you can set the internal/IGP cost as the MED while settingothers to a constant pre-defined metric as MED value.Use the set metric-type internal command in a route-map to advertise the IGP cost as the MEDto outbound EBGP peers when redistributing routes. The configured set metric value overwrites thedefault IGP cost.By using the redistribute command with the route-map command, you can specify whether a peeradvertises 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 outboundroute-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 orredistribute route-type metric) and the BGP peer outbound route-map has metric-typeinternal configured, BGP advertises the metric configured in the redistribute command asMED.168 Border Gateway Protocol IPv4 (BGPv4)
