Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

Migrating from one AS to another

I have a client who's company was split in half. One half is keeping their IP ranges and ASN, and the other half must be reconfigured with a new

ASN and IP block. We have obtained the new ASN and block from ARIN and have peering agreements in place. The routers are still advertising the old ASN, and we need to make a cutover. What is the most efficient way to cut to the new IPs and ASN with the minimum amount of downtime?

I can post configs if needed.

thanks,

Paul

  • WAN Routing and Switching
6 REPLIES
Cisco Employee

Re: Migrating from one AS to another

Hi Paul,

I have not done it but how about using the BGP 'local-as' feature. Have the neighbor AS peer with your new AS as true ebgp connection with ' local-as ' command and advertise the new IP ranges to the BGP neighbor.Once everything stabilizes then start taking out the older IP ranges from the router.

I will let someone else comment on that as well and its been a while and I need to brush up my things again.

regards,

Hall of Fame Super Silver

Re: Migrating from one AS to another

Hello Paul,

I agree with Amit the neighbor x.x.x.x local-as can be the right tool for this transition.

You may need to play with command options to achieve the desired effect

see

http://www.cisco.com/en/US/docs/ios/iproute_bgp/command/reference/irg_bgp3.html#wp1065665

in a second time you can configure each router with new AS and you can remove the local-as option.

Hope to help

Giuseppe

Re: Migrating from one AS to another

Exactly I agree with above technique...

In fact if you want minimum downtime, then it is the only possible solution i guess.

Regards,

Smitesh Kharecha

New Member

Re: Migrating from one AS to another

Thanks everyone. I was already looking into this but wanted to check here to make sure that I was going down the correct path. We're going to do this next Monday and I will post back with status and ratings.

Thanks again,

Paul

Hall of Fame Super Silver

Re: Migrating from one AS to another

Hello Paul,

during migration you may need to use route-maps to decide what to advertise to a peer in addition to the use of local-as neighbor command.

this has to be done  to avoid to advertise IP address  block 1 (associated to ASN1) with a originating AS ASN2 or viceversa

sorry if this is basic stuff, just to be more clear.

Hope to help

Giuseppe

New Member

Re: Migrating from one AS to another

Thanks, Giuseppe. This is not basic stuff to me, so I do appreciate it. I am more of a firewall guy who just inherited a very complex BGP

project.

Thanks again,
Paul
edit: We decided not to go this way; we are doing a hard cut from the old AS to the new AS. I do appreciate the help though.
268
Views
0
Helpful
6
Replies