Brocade Communications Systems ICX 7250 series, Configuration Manual

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When device ID comparison is enabled, the path comparison algorithm compares the device IDs of the neighbors that sent the otherwise
equal paths:
• If BGP4 load sharing is disabled (maximum-paths 1), the instructions in this section selects the path that came from the
neighbor with the lower device ID.
• If BGP4 load sharing is enabled, the device load shares among the remaining paths. In this case, the device ID is not used to
select a path.
NOTE
Device ID comparison is disabled by default.
To enable device ID comparison, enter the compare-routerid command at the BGP4 configuration level of the CLI.
device(config-bgp-router)# compare-routerid
Syntax: [no] compare-routerid
Configuring the device to always compare Multi-Exit Discriminators
A Multi-Exit Discriminator (MED) is a value that the BGP4 algorithm uses when it compares multiple paths received from different BGP4
neighbors in the same AS for the same route. In BGP4, a MED for a route is equivalent to its metric.
BGP4 compares the MEDs of two otherwise equivalent paths if and only if the routes were learned from the same neighboring AS. This
behavior is called deterministic MED. Deterministic MED is always enabled and cannot be disabled.
You can enable the device to always compare the MEDs, regardless of the AS information in the paths. For example, if the device
receives UPDATES for the same route from neighbors in three autonomous systems, the device can compare the MEDs of all the paths
together instead of comparing the MEDs for the paths in each autonomous system individually.
To enable this comparison, enter the always-compare-med command at the BGP4 configuration level of the CLI. This option is disabled
by default.
NOTE
By default, value 0 (most favorable) is used in MED comparison when the MED attribute is not present. The default MED
comparison results in the device favoring route paths that do not have their MEDs. Use the
med-missing-as-worst command
to force the device to regard a BGP4 route with a missing MED attribute as the least favorable route, when comparing the
MEDs of the routes.
NOTE
MED comparison is not performed for internal routes originated within the local AS or confederation unless the compare-med-
empty-aspath command is configured.
To configure the device to always compare MEDs, enter the following command.
device(config-bgp-router)# always-compare-med
Syntax: [no] always-compare-med
The following BGP4 command directs BGP4 to take the MED value into consideration even if the route has an empty as-path path
attribute.
device(config)# router bgp
device(config-bgp-router)# compare-med-empty-aspath
Syntax: [no] compare-med-empty-aspath
Optional BGP4 configuration tasks
Brocade FastIron Layer 3 Routing Configuration Guide
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