Dell Force10 Z9000 FTOS Configuration Guide for Z9000 System - Page 173

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. FTOS 8.3.1.0 and later support 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 in conjunction with the route-map command, you can specify whether a peer advertises the standard MED or uses the IGP cost as the MED. Note the following when configuring this functionality: • If the redistribute command does not have any metric configured and BGP Peer out-bound 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 out-bound route-map has metric-type internal configured, BGP advertises the metric 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. Note: When redistributing static, connected or OSPF routes, there is no metric option. Simply assign the appropriate route-map to the redistributed route. Table 8-1 gives some examples of these rules. Table 8-1. Example MED advertisement Command Settings BGP Local Routing Information Base MED Advertised to Peer WITH route-map metric-type internal WITHOUT route-map metric-type internal redistribute isis (IGP cost = 20) MED: IGP cost 20 redistribute isis route-map set metric 50 MED: IGP cost 50 redistribute isis metric 100 MED: IGP cost 100 MED = 20 MED: 50 MED: 100 MED = 0 MED: 50 MED: 100 Ignore Router-ID for some best-path calculations FTOS 8.3.1.0 and later allow you to avoid unnecessary BGP best-path transitions between external paths under certain conditions. The bgp bestpath router-id ignore command reduces network disruption caused by routing and forwarding plane changes and allows for faster convergence. Border Gateway Protocol | 173