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calculate the best path in its own. BGP add-path helps switchover to next new best path based on IGP convergence time when best path
becomes unavailable.
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.
Dell Networking OS supports 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 9. 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
redistribute isis metric 100 MED: IGP cost 100 MED: 100 MED: 100
Ignore Router-ID for Some Best-Path Calculations
Dell Networking OS 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 routing causes and forwarding plane changes and allows for
faster convergence.
Four-Byte AS Numbers
Dell Networking OS 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 are 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
176
Border Gateway Protocol IPv4 (BGPv4)