BGP Tutorial for ISP customers – Own ASN or borrowing one

   June 19, 2009

In order to setup BGP, minimum requirements are IP address and ASN. Of course your router icon_BGP.pngmust support BGP routing protocol. What is ASN? It is stands for Autonomous Systems Number that is a unique number associated with an AS. The ASN is used as an identifier to allow the AS to exchange dynamic routing information between ASes.
 

 

 

Personally, I never apply an ASN. But I was told, it is kinds of long process and no fun. If you really want to have your own, go for it. However, please see below cases you might not need to go thru the process. 

If you have one ISP link, you can borrow an ASN from your service provider.

Yes, if you have one ISP link for Internet (public), you can ask borrowable ASN for your service provider. Not sure all ISPs are providing one, but I know at least tier1 ISPs do.  

If you have two links with same ISP, you can borrow ASN from the ISP.

If you have two or more links with same ISP for redundancy or load-sharing reason, still you can borrow ASN from your ISP.

You cannot use the borrowed ASN for other ISP.

Yes, that is prohibited. You cannot use the borrowed ASN for other ISP link. For example, if you have an ISP link with VerizonBusiness. For the redundancy reason, you are adding a new ISP link which is different from current on (VerizonBusiness). Let’s new link is coming from AT&T. When you are configuring BGP with AT&T, you cannot use the borrowed ASN for new AT&T link. Normally, the borrowed ASN is working only within the ISP.

Sorry! Apply New ASN

All other case, you need to apply your own ASN. I hope no trouble to get one.

"Do not call ISP to apply ASN"

They won’t help you at all. Requesting ASN should be done by organization who will own the ASN.

 

North America – Click here
South America – Click here
ASIA – Click here
Europe – Click here
Africa – Click here

 

Good Luck!

The following article will be discussed about what BGP route table would be suitable for your network and CPE memory.

 

Author: Chris Yoon

IT professional