route-map on BGP

[vladrac-ccna]

hello everyone,

Just confirming: what will be the results of taking a route-map statement from a BGP neighbor?

Right now my configs use route-map on a peer-group and this route-map only change metrics (MED) of some prefixs Im sending out.

Question is, if I type:

no neighbor TEST route-map RMAP out

will this have any effect? will this cause any impact to the traffic flowing through this router? or do I need a clear ip bgp * soft out, to make this change work?

And if what happens after the clear ip bgp * soft out? will I lose any connection that is going through the router at the same time I use the command?

Vlad

[olorunloba]

For the change in policy, you will need to clear the BGP session for it to take effect

http://www.cisco.com/univercd/cc/td/doc/product/software/ios123/123tcr/123tip2r/ip2_c1gt.htm#wp1103308

http://www.cisco.com/en/US/products/sw/iosswrel/ps1828/products_configuration_guide_chapter09186a00800ca571.html#wp4763

If you do a soft reset, traffic will not disrupted, and you will not loose connection (assuming that the new policy does not deny the connection).

[leighharrison]

Hi there Vlad,

As you are altering the way traffic is handled between peers, you will need to reset the connection for the no route map to take effect.

Rather than "clear ip bgp * soft" it's better if you specify the peer you wish to clear. Doing a hard clear will take only a small amout of time to come back - but it will feel like forever!! A soft reset will just clear the session between the two peer and will drop some traffic, but it should not be noticable by anyone.

You can set a kron job to run when traffic is at it's least to perform the reset for you. Check out this link for specifics:-

http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124cg/hnm_c/ch30/hg_kron.pdf

If downtime is a big problem, the you could edit the route map and remove the "set med" statement. I'm not 100% sure that it would work, but I am 99% sure ;)

Regards,

LH

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[vladrac-ccna]

Hey thanks for the reply,

really cool this cron for routers, though I dont see an use for this at this moment.

Actually down time is a big problem and I'd like to make it 0, as we have 2 cores connecting to 2 routers on the ISP, I was looking for a solution to make a change without losing even the traffic flowing through the router at the moment of the change.

Vlad

[chuongnh]

Hi friends,

Your question is the basic IP BGP configuration. The route-map you apply in IP BGP in our case is use for establish IP BGP policies for Incomming traffic.

If you not use this policies, default is every routing information you need will be advertise to upstream you are connected.

The command line use best effort for change routing information for advertise.

In your case, when you use no neighbor TEST route-map RMAP out , you make your connect transparent with every traffic. When you use clear ip bgp * soft out will make the big change in your routing table with more than 180000 prefix. This reason will make your core system down.

You can make your system with strong policies and use clear ip bgp xxx.xxx.xxx.xxx soft out with separate neigbours.

Goodluck for you test.

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