From: ccna instructor (ccna20877@yahoo.com)
Date: Sun Sep 22 2002 - 16:57:21 GMT-3
Rd will install route with largest local preference.. so link 2 will be used.
Administrator of AS10 should influence weight of the route to force AS2 to use link 1.
regards
sadiq
Asim Khan wrote:Hi all,
Suppose we have 4 routers Ra, Rb, Rc and Rd. Ra is in
AS10 and Rb, Rc and Rd are in AS20 as shown below:
AS10
| loopback 1.1.1.1/32
|
Ra
/ \
Link 1 / \Link 2
-------------------------------
/ \
Rc Rb
AS20 \ /
\ /
\ /
\ /
Rd
Now suppose the Administrator of AS20 wants all
outgoing traffic to take Link 2, so he set the local
preferance on Rb for incoming routes (1.1.1.1) from Ra
as 200 and on Rc as 100(default). Rb,Rc and Rd are in
full meshed. It means to reach 1.1.1.1 router Rd will
take the path of Link 2. Now the administrator of AS10
wants to influence the incoming traffic from AS20 and
force them to use Link 1. So he set the MED 5 for all
the outgoing routes via Link 1 and the MED 10 for all
the outgoing routes via Link 2.
I know in BGP decision process local preference comes
first then MED and in general BGP policies establish
after mutual consultation of both the Administrator.
But in this particular case, when both the
administrator are in complete disagreement, which link
will be used for traffic going from AS20 to AS10.
If Link 2 is used then is there any way for
Administrator of AS10 to force AS20 to use Link 1.
Regards.
Asim Khan
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