Reference Guide

128 | Border Gateway Protocol
www.dell.com | support.dell.com
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.
Table 8-1 gives 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 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 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