Brocade Communications Systems FastIron SX 1600 Configuration Manual Download

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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

Treating missing MEDs as the worst MEDs

By default, the device favors a lower MED over a higher MED during MED comparison. Since the device assigns the value 0 to a route
path MED if the MED value is missing, the default MED comparison results in the device favoring the route paths that are missing their
MEDs.

To change this behavior so that the device favors a route that has a MED over a route that is missing its MED, enter the following
command at the BGP4 configuration level of the CLI.

device(config-bgp-router)# med-missing-as-worst

Syntax:

[no] med-missing-as-worst

NOTE

This command affects route selection only when route paths are selected based on MED comparison. It is still possible for a
route path that is missing its MED to be selected based on other criteria. For example, a route path with no MED can be
selected if its weight is larger than the weights of the other route paths.

Configuring route reflection parameters

Normally, all the BGP4 devices within an AS are fully meshed. Since each device has an IBGP session with each of the other BGP4
devices in the AS, each IBGP device has a route for each IBGP neighbor. For large autonomous systems containing many IBGP devices,
the IBGP route information in each fully-meshed IBGP device may introduce too much administrative overhead.

To avoid this overhead, you can organize your IGP devices into clusters:

•

A cluster is a group of IGP devices organized into route reflectors and route reflector clients. You configure the cluster by
assigning a cluster ID on the route reflector and identifying the IGP neighbors that are members of that cluster. All configuration

Brocade Communications Systems FastIron SX 1600, Configuration Manual

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