Am on the right path to get 3550 to decide path-iBGP?

Answered Question
May 24th, 2007

Hi, I would really appreciate your valuable input on this. Please find attached diagram showing my configuration.

a) I need to make SWITCH3550 use its internal routing processor and do intervlan routing without

relying on RouterB.

b)In case RouterB or respective link connected to RouterB fail, I need to make the SWITCH3550

detect the failure and start routing through RouterC instead.

In case RouterC or respective link connected to RouterC fail, I need to make the SWITCH3550

detect the failure and start routing through the RouterB instead.

What I have done so far (please correct me if I am wrong):

a) In order to make SWITCH3550 do the intervlan routing, I upgraded the image on the switch

and made sure it does support L2/L3. From there I need to make sure the respective VLANs

are defined. I need to do '#enable ip routing' on the switch.

My only question here is regarding the 'default-gateway' command on the switch.

Since now the switch is going to be doing the routing, am I right that I just need to eliminate the 'ip-default gateway' entry since now the SWITCH3550 (no longer RouterB) will be the gateway for this?

b) Regarding the path selection in case RouterB or RouterC paths fail, as you can see BGP is currently configured on RouterB and RouterC.

Can you give me a hint on what would be the best approach to configure the SWITCH3550 to decide which path to take in case of failure from RouterB or RouterC?

I thought something like the below. I may be totally wrong, and I appreciate if you give me a hint.

switch3550#config t

description Add access-list 1 to switch, permitting network 2.2.2.2.0

#access-list 1 permit 2.2.2.2.0 255.255.255.0

description define a route map named localpref that sets the local preference

of the route to 200 if it matches access-list 1 - and 100 if it does not

#route-map localpref 10

# match ip address 1

# set local-preference 200

# route-map localpref permit 20

# set local-preference 100

router bgp 20

neighbor <gi0/0_interface_IP_RouterB> route-map localpref in

neighbor 10.0.0.5 255.255.255.0

neighbor <gi0/0_interface_IP_RouterB>

#exit

I have this problem too.
0 votes
Correct Answer by Edison Ortiz about 9 years 6 months ago

I suggest you configure BGP on the 3550 switch have it peer with the 2 routers. The 2 routers should be configure to announce a conditional default route towards the 3550 switch only if the links are up.

You can also configure which default route is preferred from the routers by configuring local-preference at the 3550 switch.

3550 switch:

router bgp 65123

neighbor [router b] remote-as [as #]

neighbor [router c] remote-as [as #]

neighbor [router b] route-map local-pref

route-map local-pref

set local-preference 200

For conditional route advertisement, read here

http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124cg/hirp_c/ch05/brbbasic.htm#wp1111262

I don't have a lab right now to give you step-by-step commands.

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Correct Answer
Edison Ortiz Fri, 05/25/2007 - 05:45

I suggest you configure BGP on the 3550 switch have it peer with the 2 routers. The 2 routers should be configure to announce a conditional default route towards the 3550 switch only if the links are up.

You can also configure which default route is preferred from the routers by configuring local-preference at the 3550 switch.

3550 switch:

router bgp 65123

neighbor [router b] remote-as [as #]

neighbor [router c] remote-as [as #]

neighbor [router b] route-map local-pref

route-map local-pref

set local-preference 200

For conditional route advertisement, read here

http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124cg/hirp_c/ch05/brbbasic.htm#wp1111262

I don't have a lab right now to give you step-by-step commands.

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