Unanswered Question
Jun 10th, 2010

I need to configure BGP to establish neighbour relationship with my ISP. Can I provide my ISP a private AS number? or I have to provide public AS?

I have this problem too.
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Giuseppe Larosa Thu, 06/10/2010 - 10:21

Hello After111,

if you already have a public AS and this is not the only exit point to the internet the answer is you need to peer using your own public AS

if you haven't a public BGP ASN and all of you public IP addresses are taken from the ISP then the ISP will give you a private AS number to be used for the peering.

Hope to help


tprendergast Thu, 06/10/2010 - 13:07

Contact your ISP, tell them you wish to establish BGP peering for internet routing and want to use a private AS# between your router and theirs. They will give you the AS# to use.

They may also give you some additional instructions like configuration requirements, things to turn on/off in your config, etc.

francisco_1 Fri, 06/11/2010 - 03:38

As already mentioned you gonna have to use a private AS if you dont have a registered public ASN. ISP will allocate you one to use. For you info the range is 64512 - 65535 and these ranges are assigned to small enterprises tha use BGP to peer with their ISPs. Private AS ranges should not appear on the internet (You cannot advertise any prefix out that AS to the internet) as many sites may originate the same number. Thus, the AS (ISP) that provides upstream connection for private site should remove the private AS sunmbers from the AS_PATH attibute.


after1111 Fri, 06/11/2010 - 09:00

My network consists of 2 virtual private network clouds. If i run private AS with one ISP (VPN cloud 1), will this affect other ISP (VPN cloud 2)?

Giuseppe Larosa Fri, 06/11/2010 - 09:06

Hello After111,

in this case it may be helpful to choice the same private AS number so you may be able to suggest one

You may survive also using two different AS numbers, but using the same is better it allows you to have iBGP sessions

We all thought of a connection to the internet and we provided suggestions for that scenario

Hope to help



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