218 | Border Gateway Protocol IPv4 (BGPv4)w w w . d e l l . c o m | s u p p o r t . d e l l . c o m • If the redistribute command does not have any metric configured and BGP Peer out-bound route-mapdoes 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 out-bound route-map has metric-type internal configured, BGP advertises themetric configured in the redistribute command as MED.• If BGP peer out-bound route-map has metric configured, then all other metrics are overwritten by this.Table 10-1gives some examples of these rules.Ignore Router-ID for some best-path calculationsFTOS 8.3.1.0 and later allow you to avoid unnecessary BGP best-path transitions between external pathsunder certain conditions. The bgp bestpath router-id ignore command reduces network disruption causedby routing and forwarding plane changes and allows for faster convergence.4-Byte AS NumbersFTOS Version 7.7.1 and later support 4-Byte (32-bit) format when configuring Autonomous SystemNumbers (ASNs). The 4-Byte support is advertised as a new BGP capability (4-BYTE-AS) in the OPENmessage. If a 4-Byte BGP speaker has sent and received this capability from another speaker, all themessages will be 4-octet. The behavior of a 4-Byte BGP speaker will be different with the peer dependingon whether the peer is 4-Byte or 2-Byte BGP speaker.Note: When redistributing static, connected or OSPF routes, there is no metric option. Simply assign theappropriate route-map to the redistributed route.Table 10-1. Example MED advertisementCommand SettingsBGP Local RoutingInformation Base MED Advertised to PeerWITH route-mapmetric-type internalWITHOUT route-mapmetric-type internalredistribute isis(IGP cost = 20)MED: IGP cost 20 MED = 20 MED = 0redistribute isisroute-map set metric 50MED: IGP cost 50 MED: 50 MED: 50redistribute isis metric 100 MED: IGP cost 100 MED: 100 MED: 100
