Users Guide

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-type metric) and the BGP peer outbound route-map has metric-type internal
configured, BGP advertises the metric configured in 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 8. Redistributed Route Rules
Command Settings BGP Local Routing
Information Base
MED Advertised to Peer
WITH route-map metric-
type internal
MED Advertised to Peer
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 MED: 50 MED: 50
redistribute isis metric
100
MED: IGP cost 100 MED: 100 MED: 100
Ignore Router-ID for Some Best-Path
Calculations
You can 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.
Four-Byte AS Numbers
The 4-Byte (32-bit) format is supported to configure 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 is different with the peer depending on whether the peer is a 4-Byte or 2-
Byte BGP speaker.
Where the 2-Byte format is 1-65535, the 4-Byte format is 1-4294967295. Enter AS numbers using the
traditional format. If the ASN is greater than 65535, the dot format is shown when using the show ip bgp
commands. For example, an ASN entered as 3183856184 appears in the show commands as 48581.51768; an
ASN of 65123 is shown as 65123. To calculate the comparable dot format for an ASN from a traditional
format, use ASN/65536. ASN%65536.
Border Gateway Protocol IPv4 (BGPv4) 203