BGP Dual AS Configuration

[pkhatri]

Hi all,

Just looking at the feature note for this feature at the following url, and I am a bit confused.

http://www.cisco.com/en/US/partner/products/sw/iosswrel/ps1829/products_feature_guide09186a00802c0816.html

Under the section "Dual-AS Configuration: Example", it states that "the transition needs to occur without interrupting service to Router 3". I fail to see how that is possible without service interruption. From what I can gather, the following is being done:

1. The BGP peering is being moved from Router2 to Router1 (including the physical serial link) - that's gotta take a hit.

2. Since Router1 is using the dual-as keyword, when Router3 changes its peering to be to AS100 now, no changes need to be done on Router1. However, the bgp session will still take a hit.

3. When the local-as statement is removed on Router1 (after Router3 is migrated), there is no hit to the BGP peering session.

Can someone explain ?

I've got another query regarding the same document - this time it's example "Replace-AS Configuration: Example"

The config used is:

router bgp 64512

neighbor 10.3.3.33 local-as 300 no-prepend replace-as

neighbor 10.3.3.33 remove-private-AS

If the replace-as keyword is used, I understand that this bgp speaker will only pre-pend AS 300 to the AS-Path on outgoing updates, and not AS 64512 followed by AS 300. So why do we need the remove-private-as statement ?

All responses appreciated.

Cheers,

Paresh.

[pkhatri]

Anyone at all ??

Paresh.

[Harold Ritter]

This configration example need to be revised. Router 1 and 2 configuration are referring to the same router. Router 2 shows the configuration before the migration from AS 200 to 100 and router 1 shows the after migration configuration.

As you mentioned, going from configuration 1 to 2 will reset the session.

As for your second comment, you are correct the remove-private-AS would not be required in this scenario.

I will report this to the documentation team.

Hope this helps,

[pkhatri]

Thanks again, dude...

Are you happy to take more of these issues up or is there a better process to get these changes done ? Pls do let me know..

Regards,

Paresh.

[Harold Ritter]

Paresh,

It is perfectly fine with me. If I can be of any help in investigating these issues and then report them to the documentation team, it makes my day. I would like to thank you as well for taking the time to review these documents. It probably helps a whole lot of other people.

Thanks,

[pkhatri]

Cool...

I've got a few more of these that I might send to you shortly. Would it help to use a prefix on the subject for such conversations so that we can make sure that you do see them ?

Thanks.

Paresh.

[Harold Ritter]

"Documentation:" should be fine.

Thanks,