Brocade Multi-Service IronWare Routing Configuration Guide (Supporting R05.6.00) User Manual
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Multi-Service IronWare Routing Configuration Guide
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Configuring the device to always compare Multi-Exit Discriminators
The ip-addr and ip-mask parameters specify the aggregate value for the networks. Specify 0 for the
host portion and for the network portion that differs among the networks in the aggregate. For
example, to aggregate 10.0.1.0/24, 10.0.2.0/24, and 10.0.3.0/24, enter the IP address 10.0.0.0
and the network mask 255.255.0.0.
The as-set parameter causes the device to aggregate AS-path information for all the routes in the
aggregate address into a single AS-path.
The summary-only parameter prevents the device from advertising more specific routes contained
within the aggregate route.
The suppress-map map-name parameter prevents the more specific routes contained in the
specified route map from being advertised.
The advertise-map map-name parameter configures the device to advertise the more specific
routes in the specified route map.
The attribute-map map-name parameter configures the device to set attributes for the aggregate
routes based on the specified route map.
NOTE
For the suppress-map, advertise-map, and attribute-map parameters, the route map must already
be defined. Refer to “
on page 81 for information on defining a route map.
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 ASs,
the device can compare the MEDs of all the paths together instead of comparing the MEDs for the
paths in each AS 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.
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.
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.
Brocade(config-bgp)# always-compare-med