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New Member

BGP attributes LOCAL_PREF and MULTI_EXIT_DISC

Hello,

I have a very basic setup. two routers connected together via two links (one short hall ethernet circuit and one E1 between sited)

Running IBGP peering over both links. Both neighbors has route-maps with the setting for clarity.

If I do nothing, RTR2 to get to iBGP learned routes behind RTR1 will use the serial-link as the neighbor IP address is lower.

Now, I thought I may have two options to either set the MED (metric) or the local_pref with a route-map on RTR1 outbound to RTR2, but the MED option does not work. It sets the MED on rtr2 but the BGP table still uses the serial.

WILL MULTI_EXIT_DISC work with iBGP links? like I say, the values in the iBGP table on rtr2 reflect the route-map setting the MED which is config'd on RTR1.

CONFIG on RTR1 (no config for attribs on RTR2)

-------------SET-MED---------------------------------

!

router bgp 65001

neighbor 3.3.3.2 remote-as 65001

neighbor 3.3.3.2 route-map SET-MED-ETHERNET out

neighbor 2.2.2.2 remote-as 65001

neighbor 2.2.2.2 route-map SET-MED-SERIAL out

!

route-map SET-MED-SERIAL permit 10

match as-path 11

set metric 1000

!

route-map SET-MED-SERIAL permit 20

!

!

no route-map SET-MED-ETHERNET

route-map SET-MED-ETHERNET permit 10

match as-path 11

set metric 500

!

route-map SET-MED-ETHERNET permit 20

or

-------------SET-LOCALPREF---------------------------------

router bgp 65001

neighbor 1.1.1.2 remote-as 65001

neighbor 1.1.1.2 route-map SET-LOCALPREF-ETHERNET out

neighbor 2.2.2.2 remote-as 65001

neighbor 2.2.2.2 route-map SET-LOCALPREF-ETHERNET out

!

route-map SET-LOCALPREF-SERIAL permit 10

match as-path 11

set local-pref 80

!

route-map SET-MED-SERIAL permit 20

!

!

route-map SET-LOCALPREF-ETHERNET permit 10

match as-path 11

set local-pref 90

!

route-map SET-MED-ETHERNET permit 20

!

2 ACCEPTED SOLUTIONS

Accepted Solutions
Cisco Employee

Re: BGP attributes LOCAL_PREF and MULTI_EXIT_DISC

Yes, MED should work on iBGP links.

What do the routes look like on rtr2?? Keep in mind that the MED is towards the end of the selection process *and* only compared from routes from the same neighbor AS. Either of these two factors may not be letting you reach the comparison point.

OTOH, LOCAL_PREF is compared at the start of the selection process *and* for all paths (regardless of where they came from).

To give you a definite answer, I would have to see the paths as seen by rtr2. If you don't want to post them here, you can send them to me directly: alvaro@cisco.com.

Regards,

Alvaro.

New Member

Re: BGP attributes LOCAL_PREF and MULTI_EXIT_DISC

Please try sh ip bgp filter-list 11 to see whether the routes you want to set MED on match the ip as-path access-list 11.

Regards

Ian

2 REPLIES
Cisco Employee

Re: BGP attributes LOCAL_PREF and MULTI_EXIT_DISC

Yes, MED should work on iBGP links.

What do the routes look like on rtr2?? Keep in mind that the MED is towards the end of the selection process *and* only compared from routes from the same neighbor AS. Either of these two factors may not be letting you reach the comparison point.

OTOH, LOCAL_PREF is compared at the start of the selection process *and* for all paths (regardless of where they came from).

To give you a definite answer, I would have to see the paths as seen by rtr2. If you don't want to post them here, you can send them to me directly: alvaro@cisco.com.

Regards,

Alvaro.

New Member

Re: BGP attributes LOCAL_PREF and MULTI_EXIT_DISC

Please try sh ip bgp filter-list 11 to see whether the routes you want to set MED on match the ip as-path access-list 11.

Regards

Ian

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