Question : Understanding BGP - Looking Glass

Can someone give me a quick high level overview of BGP, as it relates to Internet routing tables, and looking glass sites?

Specifically, my small site will be moving ISPs, from MCI to AT&T.  Our /20 network is being advertised by MCI right now.  The routers we manage have nothing to do with it, we just static route to an MCI router, that handles the BGP.  But it's our address space (asigned to us), not MCI.  So when we move to AT&T, they will start to advertise that address space.

The ISPs assure us that they will work together to handle the routing transition.  Which is fine.  But I'd like to at least understand a little bit about how it works, and how I can verify (using Looking Glass sites I think?) who is advertising it?

Thanks
Shane

Answer : Understanding BGP - Looking Glass

Hi.

First of all, I'd say it's hard to give a "high level overview" of such a complex routing protocol as BGP. And if you get one, then it wouldn't be enough for the "overview" level you want. However, here's my try.

Now, a definition: On the Internet, an autonomous system (AS) is the unit of router policy, either a single network or a group of networks that is controlled by a common network administrator (or group of administrators) on behalf of a single administrative entity (such as a university, a business enterprise, or a business division). An autonomous system is also sometimes referred to as a routing domain. An autonomous system is assigned a globally unique number, sometimes called an Autonomous System Number (ASN). [Definition taken from http://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci213662,00.html]

BGP is based on AS decisions. It can function in intra-AS decisions and inter-AS decisions. Regarding ISPs, usually it works as inter-AS routing protocol. The advantage of the BGP is it's flexible configuration - hence its complexity. BGP configuration is based on attributes (properties) - these properties or attributes, when properly combined it forms what it's called as "routing policies".

Concluding, BGP is a routing protocol based that allows policies based decisions in a very flexible and granular manner.



Here are some links as well:

http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/bgp.htm
http://www.cse.ucsc.edu/research/ccrg/publications/brad.globalinternet96.pdf
http://24.237.160.4/files/networking/Infocom%20stuff/Infocom2001%20CD/DATA00/03D_1.PDF

Cheers