Cisco Support Community
Community Member

AS plan for registration. IANA.private AS

There are only 65535 AS.

If Company A want to configure multihoming for Internet with BGP what AS number it uses? Private? AS taked from IANA?

Can you explain me this step?

Also interested in detail plan of registration AS.Where I can read this?


Re: AS plan for registration. IANA.private AS


The Private AS number in BGP starts from 64512 -to- 65535. So (65535)is not the Only private AS.

Company A could go with both solutions in Multihoming:

1) If multihoming with the Same Service Provider, then the ISP has to assigh and agree on Company's A private AS.

2) If multihoming with different Service Providers, then Both ISP has to agee on Company's A private AS.

3) To prevent from ISP mistake, you should always apply the appropriate filters in place.

For Any AS Request/registration, Pls follow the instructions in the bellow document:



Community Member

Re: AS plan for registration. IANA.private AS

But if AS is "private", why I should register it RIPE? Am I right?

How can RIPE control private AS, therefore this private AS with number forexample 64555 can be hundreds in the Europe?

Hall of Fame Super Silver

Re: AS plan for registration. IANA.private AS

Hello Alexandr,

private AS numbers are there to allow to use BGP between a service provider and a customer without the need for a public AS.

What happens with private AS is similar to private ip addresses RFC 1918:

they don't appear in internet

in internet the as path terminates in a public AS number that belongs to the ISP.

the ISP has faculty to override the private AS or to remove it when talking to other providers

So every provider can use all the 1024 private AS numbers for its customers

Hope to help


Community Member

Re: AS plan for registration. IANA.private AS

Consider using private AS space (64512-65535) only if you are multihoming with the same provider (eg: you have multiple exit points to the same provider). Note: you do not need to register private as anywhere. It's just a matter of mutual agreement between you and your Service Provider of what private AS you will use.

If you have multiple providers, consider using a registered AS number.

The idea behind the private AS is that you will negotiate the usage of a private AS with your SP. Say 64512. Remember your service provider has also a public AS (eg AS100).

The provider will see your routes within their AS with AS64512. When they will advertise your routes to any upstream AS they will strip out your AS 64512 and your routes will appear as coming from AS100

Imagine now using a private AS with 2 service provider.

What will happen if both strip your private AS and advertise with their own? Your routes will appear as being sourced from 2 Public AS numbers. Now that can still work, but is not correct/recommended.

I advise you to read:

Community Member

Re: AS plan for registration. IANA.private AS


And when I should negotiate something with RIPE? When I want register public AS?

Forexample, if my coworker said that now AS is registered in RIPE - what does it mean in networking? Also we have backup ISP

Community Member

Re: AS plan for registration. IANA.private AS

I'm guessing he just means now you have a public AS registered with RIPE. As i said private AS is not registered with RIPE. RIPE does not even know about whatever private AS people are running (they are not visible in the internet routing tables)

CreatePlease to create content