Changing administrative distances – Brocade BigIron RX Series Configuration Guide User Manual
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BigIron RX Series Configuration Guide
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Changing the default metric used for redistribution
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NOTE
To set the local preference for individual routes, use route maps. Refer to
page 876. Refer to
“How BGP4 selects a path for a route”
on page 816 for information about the
BGP4 algorithm.
To change the default local preference to 200, enter the following command.
BigIron RX(config-bgp)# default-local-preference 200
Syntax: default-local-preference <num>
The <num> parameter indicates the preference and can be a value from 0 – 4294967295.
Changing the default metric used for redistribution
The BigIron RX can redistribute directly connected routes, static IP routes, RIP routes, ISIS routes,
and OSPF routes into BGP4. By default, BGP uses zero (0) for direct connected routes and the
metric (MED) value of IGP routes in the IP route table. The MED is a global parameter that specifies
the cost that will be applied to all routes, if assigned, when they are redistributed into BGP4. When
routes are selected, lower metric values are preferred over higher metric values. The default, the
BGP4 MED value is not assigned.
NOTE
RIP, ISIS, and OSPF also have default metric parameters. The parameters are set independently for
each protocol and have different ranges.
To change the default metric to 40, enter the following command.
BigIron RX(config-bgp)# default-metric 40
Syntax: default-metric <value>
The <value> indicates the metric and can be a value from 0 – 4294967295.
Changing administrative distances
The BigIron RX can learn about networks from various protocols, including the EBGP portion of
BGP4 and IGPs such as OSPF, ISIS, and RIP. Consequently, the routes to a network may differ
depending on the protocol from which the routes were learned.
To select one route over another based on the source of the route information, the device can use
the administrative distances assigned to the sources. The administrative distance is a
protocol-independent metric that IP routers use to compare routes from different sources.
The device re-advertises a learned best BGP4 route to the device’s neighbors even when the route
table manager does not also select that route for installation in the IP route table. The best BGP4
route is the BGP4 path that BGP selects based on comparison of the paths’ BGP4 route
parameters. Refer to
“How BGP4 selects a path for a route”
When selecting a route from among different sources (BGP4, OSPF, RIP, ISIS, static routes, and so
on), the software compares the routes on the basis of each route’s administrative distance. If the
administrative distance of the paths is lower than the administrative distance of paths from other
sources (such as static IP routes, RIP, or OSPF), the BGP4 paths are installed in the IP route table.