In the example, AS 256 receives route
updates for network 170.10.0.0 from AS 100 and AS 300.
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Lab
Activity |
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In
this lab, you will learn how to configure the
local preference attribute to
indicate a preferred route to a destination with multiple routes. |
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There are two ways to set local
preference:
- Using the bgp default
local preference Command
- Using a route map to set local
preference
Note: Click on topology to view
command outputs.
Using the bgp
default local preference Command
The configurations in the example use
the bgp default local preference
router
configuration command to set the local preference attribute on
routers C and D.
Router C's configuration causes it to set the local preference of
all updates from AS 300 to 150, and router D's configuration causes
it to set the local preference for all updates from AS 100 to 200.
Because local preference is exchanged within the AS, both routers C
and D determine that updates regarding network 170.10.0.0 have a
higher local preference when they come from AS 300 than when they
come from AS 100. As a result, all traffic in AS 256 destined for
network 170.10.0.0 is sent to router D.
Using a Route Map to Set Local
Preference
Route maps provide more flexibility
than the bgp default local preference
configuration command. When the bgp
default local preference command is used on router D in the example, the
local preference attribute of all updates received by router D will be set to 200,
including updates from AS 34. The following configuration uses a
route map to set the local preference attribute on router D
specifically for updates regarding AS 300:
With this configuration, the local preference
attribute of any update coming from AS 300 is set to 200.
Instance 20 of the SETLOCALIN route map accepts all other routes.
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