What's the meaning of BGP prefix? [closed]

Question

Through this website IP to ASN lookup,I can get a series of results about the ASN,but I can't find the meaning of BGP prefix.Maybe I know what it is,however,how it works?

Is there anyone who can tell me the role BGP prefix plays in the ASN system?

Jon

Network Engineering Stack Exchange – Lavenialaver

Answer 1

A prefix announced in BGP consists of the IPv4 or IPv6 address block being announced and also a path of AS numbers, indicating which ASNs the traffic must pass through to reach the announced address block.

A BGP prefix would look something like (IPv4): 701 1239 42 206.24.14.0/24. The /24 part is referred to as a CIDR mask. The /24 indicates that the first 24 bits in the address block is the ?network? part of the address block.

Robtex provides BGP prefixes for each AS number (ex. https://www.robtex.com/as/as42.html#bgp)

Determinant

Answer 2

First, let us clarify the relationship among an IP prefix, a route, and BGP NLRI.

The primary function of BGP protocol is to exchange network reachability information (i.e. routes) between BGP speakers. Routes are advertised between BGP peers in BGP update messages.

A route contains 1) a set of destinations as an IP prefix which is carried in the Network Layer Reachability Information (NLRI) field in a BGP update message, and 2) the attributes of the path to the destinations, which is carried in the path attributes field in a BGP update message.

Specifically, in BGP update message, an IP prefix is encoded as a 2-tuple form (length, prefix). Also, BGP has an AS_PATH path attribute which is a list of AS numbers through which the routes in this BGP update message has passed. For more details about how AS_PATH works, you can refer to RFC4271 section 5.1.2.

And of course, a BGP session (eBGP or iBGP) needs to be successfully established in order to exchange BGP update messages.

So now we can summary the answer for your question, a prefix is a part of a BGP route, and will be exchanged between BGP neighbors in a BGP update message.

Nigelniger

Answer 3

BGP protocol is responsible to exchange IP blocks advertisement (IP prefixes) between Autonomous Systems.

So when you run a query on Cymru IP tool what you see is the IP blocks advertised on Internet using BGP protocol as they reach Cymru routers. In other words this is the internet routing table from their perspective.

Tools like this has a name: looking glass. There's a lot of LG's on globe as they're a very nice tool to understand how IP blocks spread around Internet. BGP play is another project that uses some LG's to mount a graphic view from the Internet prefixes. Check it: https://stat.ripe.net/bgplay

Finery

Answer 4

In BGP, a set of destinations is advertised as an IP prefix, eliminating the concept of network "class" within BGP.

Leclerc