BGP MED are not being advertised to EBGP NEIGHBOR

[s.ferreira]

We have a problem. I'm redistributing OSPF into BGP but when there are changes on my internal routing protocol that affect my internal metrics and subsequently the MED's those changes are

not getting propagated to my EBGP neighbors. The new MED values are not being sent to my ISP. I have to manually reset the connection for changes to take place. I know the BGP UPDATE messages should be sent when there are changes in the BGP attributes.

I'm using 12.3.6 and 12.3.9 IOS code.

I know there is a bgp soft reset command but that is still manual. Is there a way to make this happen without user intervention? I want the changes on my interior to automatically be reflected outbound to my EBGP neighbors without user intervention within a reasonable amount of time.

[Harold Ritter]

For stability purposes, BGP will wait 600 seconds to re-advertise a path if the MED has changed. Otherwise, constant route flapping in your IGP could result in constant route flapping on the Internet as well.

The following hidden command can be used to change this default behavior:

bgp dynamic-med-interval <60-BIG_NUMBER>

Hope this helps,

[Harold Ritter]

One more thing. The change of IGP metric will not automatically be reflected in the BGP MED. You need the following configuration to achieve that goal:

router bgp

neighbor x.x.x.x route-map MedInternal out

!

route-map MedInternal permit 10

set metric-type internal

This configuration in conjunction with the knob I provided in my first message should help you to achieve your goal.

Hope this helps,

[s.ferreira]

Thanks, yeah I figured out that we needed the set metric-type internal, it works even without the other command.

Sincerely,

Steve Ferreira

[Harold Ritter]

Have you tried multiple metric changes? The 600 seconds rules applies to the BGP update, so if it has been more than 600 seconds since the last update and you change the MED then the BGP update will be sent right away. Otherwise, BGP will wait until the timer expires before sending the new update with the changed MED. Just out of curiosity what level of code are you running?

Hope this helps,

[s.ferreira]

12.3T(6) and 9

[Harold Ritter]

the 600 seccond time applies to that level of code as well.

Hope this helps,

[safe]

Dear all,

How to use MED in ISP Environment if 2 different Upstream connection taken & Upstream alerady set Local prefrence in there network.

Any other way to advertise /28,/30 network in bgp announcement or is it compulsary to use class C block always.

Thanks

SAM