218 | Border Gateway Protocol IPv4 (BGPv4)
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• 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.
Table 10-1gives some examples of these rules.
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.
4-Byte AS Numbers
FTOS Version 7.7.1 and later support 4-Byte (32-bit) format when configuring Autonomous System
Numbers (ASNs). The 4-Byte support is advertised as a new BGP capability (4-BYTE-AS) in the OPEN
message. If a 4-Byte BGP speaker has sent and received this capability from another speaker, all the
messages will be 4-octet. The behavior of a 4-Byte BGP speaker will be different with the peer depending
on 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 the
appropriate route-map to the redistributed route.
Table 10-1. 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 MED = 20 MED = 0
redistribute isis
route-map set metric 50
MED: IGP cost 50 MED: 50 MED: 50
redistribute isis metric 100 MED: IGP cost 100 MED: 100 MED: 100
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