BGP and same ASN number

[prashantrecon]

Hi Team,

I have a doubt , I want to use same ASN number at different sites with different- different ISP.(consider i have public ip range 1.1.1.0/24 )

consider I have a public server with ip 1.1.1.1 at site A and and if i advertise same Public pool at B site , how return traffic know that if it has to come at site A or B.

or if some one from Internet want to access this 1.1.1.1 public server , Is that request will come to on Site A router or Site B router . 

Regards,

Prashant

[JohnTylerPearce]

Prashant,

Are your two sites connected in any way? Or are they completely separate sites running the same AS?

Now, if you have for examle (1.1.1.0/24), and advertise this network out to the network, you could do AS_PATH prepending to try and equal out AS_PATH lengths for both routes, but I wouldn't recommend doing it this way.

I'm assuming these are Provider Independent addresses, so you could advertise out specific prefixes with a /32, and use AS_PATH prepending as well, for kind of a "double shot" so to speak.

You could also split up the /24 into two /25s, with one /25 being in Site A and another being in Site B.

[prashantrecon]

Hi John,

Thanks for reply

These sites are not connected and they are completly separate sites runing same AS.

Yes my public Pool is From APNIC and it is ISP provider independent .

i have ask my both ISP and they are saying that they can not split /24 pool in /25 ,with one at site A another at site B.

I basically looking for a DR solution and if my site A goes down then my public ip 1.1.1.1 would be UP and work.

any suggestion ?

Regards,

Prashant

[JohnTylerPearce]

Prashant,

Thanks for the reply.

If you want to do this as a DR solution, this can be done pretty easy.

You can have the eBGP link going to your ISP that you want to use as backup, configure AS_PATH prepending, so it should never be used, for incoming traffic, unless the primary eBGP link goes down.

So you could do the following for example: (You can configure it out you like, this is jus an example)

access-list 1 permit 1.1.1.0 255.255.255.0

route-map ASPATH_PREPEND permit 10

match ip address 1

set as-path preped ASN ASN ASN

router bgp ASN

neighbor route-map ASPATH_PREPEND out

As long as your primary ISP eBGP peer doesnt' go down, the 1.1.1.0/24 NLRI information from the Internet should always be taken, since it has a shorter AS_PATH

Feel free to research AS_PATH prepending to make sure this is something you want to implement, but this would be my suggestion.

[prashantrecon]

Hi John,

Thanks a lot for help

i have done some research on As path prepend and i think this will work.

i will let you know as i will complete my testing on test environment.

Regards,

Prashant

[networkcar.com]

Hi Prashant,

I had the exact same scenario.

I have my own, provider independent Public AS and a /23 Public IP.

We have 2 DC at 2 different locations with 2 Internet Routers at each site. Each receiving a FULL BGP table. So in a nutshell, I have 2 Datacenters ( San Diego and Phoenix), 4 ISP's (2 per DC),. Each site has redundant ISP's (eBGP to ISP and a iBGP between the 2 routers sharing the full internet routes) and I want to start advertising my new ARIN /23 IP via ANYCAST from the 2 DC's to all 4 ISP's.

DC # 2 is NOT live yet and I was wondering if I can use my same San Diego DC ARIN ASN and advertise my subnet?

Any feedback will be greatly appreciated.