Aggregating Routes Advertised To Bgp4 Neighbors; Configuring The Device To Always Compare Meds - Dell PowerConnect B-RX Configuration Manual

Aggregating routes advertised to BGP4 neighbors

By default, the BigIron RX advertises individual routes for all the networks. The aggregation feature
allows you to configure the device to aggregate routes in a range of networks into a single network
prefix. For example, without aggregation, the device will individually advertise routes for networks
207.95.1.0/24, 207.95.2.0/24, and 207.95.3.0/24. You can configure the device to instead send
a single, aggregate route for the networks. The aggregate route can be advertised as
207.95.0.0/16.
To aggregate routes for 209.157.22.0/24, 209.157.23.0/24, and 209.157.24.0/24, enter the
following command.
BigIron RX(config-bgp)# aggregate-address 209.157.0.0 255.255.0.0
Syntax: aggregate-address <ip-addr> <ip-mask> [as-set] [summary-only] [suppress-map
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 router to aggregate AS-path information for all the routes in the
aggregate address into a single AS-path.
The summary-only parameter prevents the router 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 router to advertise the more specific
routes in the specified route map.
The attribute-map <map-name> parameter configures the router 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

Configuring the device to always compare MEDs

A Multi-Exit Discriminator (MED) is a value that the BGP4 algorithm uses when comparing multiple
paths received from different BGP4 neighbors in the same AS for the same route. In BGP4, a
route's MED 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.
In addition, you can enable the device to always compare the MEDs, regardless of the AS
information in the paths. To enable this comparison, enter the always-compare-med command at
the BGP4 configuration level of the CLI. This option is disabled by default.
BigIron RX Series Configuration Guide
53-1002253-01
<map-name>] [advertise-map <map-name>] [attribute-map <map-name>]
""Defining route maps"
Aggregating routes advertised to BGP4 neighbors
on page 801 for information on defining a route map.
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