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BGP and private AS

Hi guys!

What's your advise? (except "get your CCNP")

We are running web site on VM with public IP address.

Company planning to move to other location and get service from 2 different ISP.

To provide failure tolerance I plan to organize BGP with private AS.

Correct me if I wrong:

I do need to regulate number of AS from 64512 to 65535 and lease pool of IP addresses from one ISP and advertise to other one?

Thank you for review and help!

VIP Advisor

I think you would need to talk to your providers first and find out what criteria both use to allow you to advertise Public IP addresses into their AS(s).

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the AS 64512 to 65535 are private AS numbers (like RFC 1918) and can't be used to peer/do eBGP with upstream service providers.

you should contact your RIR to get/register public ASN. refer useful links:


Hi John!

Somehow it's possible to get rid of private AS number on the side of ISP and place it's own ASN.

Please take a look my answer to Georg.



just to be sure there is no misunderstanding: you cannot peer with an ISP using a private AS. If you want your router to connect with an ISP, your provider will assign you a public AS. The public range has been extended by using a 4 byte number, so the original public range, AS 1 through 64,495 has now been extended to over 4 billion possible AS numbers.

That said, you provider can strip private AS-numbers from incoming updates, with the remove-private-as peer command, e.g.:

neighbor remove-private-as


Hello, Georg!

Keith Barker told: "You can peer with ISP by using private AS"

I was calling to one of ISP, they told

- Yes, we can do that: "Which number of private AS would you take?"

Another ISP told me: You can peer to us with private AS but you do need take two uplinks to us. - That's how it works.

I did clarify a bit that quetions.

But I did't find the second ISP which would accept just one uplink to them with private AS.

But if I will. Will it works like that: I will lease network /24 from one ISP and advertise it by private AS to other one, or it does't work like what?

VIP Expert


in addition to the other posts, the link below has a pretty straight forward explanation of the necessary steps:

Setting Up a Redundant Internet Connection With BGP


Hi Georg!

Thanks for link, I did read it. But there no clear information about private AS and how ISP strip off private AS number and replacing with their own for further BGP routing.

All I need it just understand how to configure BGP and private AS when I will have two ISP.

And what type of configuration will perform ISP to strip off my private AS.

btw in that situation do I need still to lease PI IP addresses or it's will work with leased IP from ISP?

Here is some pics which I did found from CBT nuggets course  "CCNP R&S" by Keith Barker

And his answer about "strip of private AS number"

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