MBGP uses either an IPv4 address configured on the interface (which is used to establish the IPv6 session) or a stable IPv4 address that isavailable in the box as the next-hop address. As a result, while advertising an IPv6 network, exchange of IPv4 routes does not lead tomartian next-hop message logs.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 intoBGP.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 same address prefix without replacingexisting paths with new ones. By default, a BGP speaker advertises only the best path to its peers for a given address prefix. If the bestpath becomes unavailable, the BGP speaker withdraws its path from its local RIB and recalculates a new best path. This situation requiresboth IGP and BGP convergence and can be a lengthy process. BGP add-path also helps switchover to the next new best path when thecurrent 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 each peer for redistributed routes. Forsome peers you can set the internal/IGP cost as the MED while setting others 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 MED to outbound EBGP peers whenredistributing 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 oruses 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-typemetric) and the BGP peer outbound route-map has metric-type internal configured, BGP advertises the metric configuredin 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.Table 10. Redistributed Route RulesCommand Settings BGP Local Routing InformationBase MED Advertised to PeerWITH route-map metric-typeinternalMED Advertised to PeerWITHOUT route-map metric-type internalredistribute isis (IGP cost = 20) MED: IGP cost 20 MED = 20 MED = 0redistribute isis route-map setmetric 50MED: IGP cost 50 MED: 50 MED: 50 MED: 50 MED: 50redistribute isis metric 100 MED: IGP cost 100 MED: 100 MED: 100186 Border Gateway Protocol IPv4 (BGPv4)
