BGP Large Communities: RFC 8092

Well… seems I have been sleeping for a while. Draft BGP Large Communities about which I wrote a little while ago here already go to it’s final stage about a month ago. RFC 8092 was published mid February/2017.

Looking at the differences between draft 06 (published October/2016) and RFC 8092 little was changed except for small language corrections and the “Reserved Large BGP Community values” section.

Will you be able to play with Cisco routers? Not yet! The “big ones” like Cisco and Juniper have not implemented any draft or the RFC. But if you want to stay updated please keep looking at the implementations page. IXPs (Internet Exchange Point) thatfrequently use servers running opensource routing software can already upgrade their code and start testing and defining policies and community values. This Internet Draft is a good start.

To better understand what this new BGP attribute is, have a look at my post from 2016: Large BGP Communities (Internet Draft).

Large BGP Communities (Internet Draft)

This week I was mindlessly going around “the internet” and stumbled upon an interesting IETF RFC draft from the Inter Domain Routing Working Group (IDR WG). The draft is for Large BGP Communities and is currently its 6th version.

What is it why do we need it?

You probably heard of BGP communities. This BGP attribute is defined in RFC 1997 is one of the most used attributes to help service providers apply specific routing policies to a group of prefixes sharing some common property.

BGP Communities are 4 Byte (32bit) values represented as A:B, where A is the decimal representation of the first 2 Bytes and B the decimal representation of the lower 2 Bytes. It is common practice to use the first 2 Bytes as an AS number and the last 2 Bytes to convey information to upstream routers (such as a Local Preference value to be set).

But there is a problem with this. RFC 1997 has been in use since 1996 and since then a lot has changed. One of these changes is the RFC6793 which defined the capability of BGP speakers to use 4 Byte (32bit) AS numbers instead of the shorter 2 Byte (16 bit) AS numbers. Continue reading