Administrator Guide

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-dened metric as MED
value.
The Dell Networking OS version 8.3.1.0 and later support conguring 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 congured set metric value
overwrites the default IGP cost.
By using the redistribute command with the route-map command, you can specify whether a peer advertises the standard
MED or uses the IGP cost as the MED.
When conguring this functionality:
• If the redistribute command does not have metric congured and the BGP peer outbound route-map does have
metric-type internal congured, BGP advertises the IGP cost as MED.
• If the redistribute command has metric congured (route-map set metric or redistribute route-type
metric) and the BGP peer outbound route-map has metric-type internal congured, BGP advertises the metric
congured in the redistribute command as MED.
• If BGP peer outbound route-map has metric congured, all other metrics are overwritten by this conguration.
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 6. 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
The Dell Networking OS version 8.3.1.0 and later allows 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.
Four-Byte AS Numbers
The Dell Networking OS version 7.7.1 and later supports 4-Byte (32-bit) format when conguring 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 dierent
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)
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