Users' questions

What is no export community?

What is no export community?

The no-export BGP community is defined in RFC 1997: “All routes received carrying a [BGP] communities attribute containing this value MUST NOT be advertised outside a BGP confederation boundary” (i.e. outside our own AS, or across regular EBGP sessions).

What does no export mean?

If you set the community as no-export when RTB/AS100 advertises routes to RTD/AS300, then RTD/AS300 receives the route with the community no-export. This means that the route will be used inside AS300, but will not go any further.

What are BGP communities?

A BGP community is an optional, transitive BGP attribute that is recognized and passed to other BGP peers. You might see a BGP community as a tag attached to the BGP routes exchanged between two BGP peers. ‍ To get started, let’s look at what a BGP community set to a route looks like in an Update message.

What are the well known communities of the BGP community attribute?

Here are the 4 well known BGP communities:

  • Internet: advertise the prefix to all BGP neighbors.
  • No-Advertise: don’t advertise the prefix to any BGP neighbors.
  • No-Export: don’t advertise the prefix to any eBGP neighbors.
  • Local-AS: don’t advertise the prefix outside of the sub-AS (this one is used for BGP confederations).

How does the BGP community no export work?

BGP Community No Export. The well known BGP community no export tells BGP neighbors to advertise a prefix only to iBGP neighbors. If you are not sure what BGP communities are and how they work then I advise you to read my introduction to BGP communities first before you continue. Having said that, let’s take a look at a configuration example.

How to advertise prefixes in BGP no export?

BGP No-Export ensures prefixes to not get advertised outside of an AS. In the diagram below, I’m going to configure R2 to advertise the network to R3 using the no-export community so that R3 does not advertise this to R4. Let’s jump on R4 to ensure the prefix has been received. Okay let’s set this up.

Can you advertise a route in BGP Neigbors?

The routes coming with this attribute, are not advertised to eBGP peers. So, you can advertise routes to iBGP neigbors with this Well Known BGP Communities. With this BGP No-Export Community, we prevent our Autonomous System also to become a Transit AS.

What is the value of no export community?

The value of No-Export Community is FFFF:FF01. This No-Advertise Community prevents advertising the routes to any peer, internal or external. So, the router that gets this type route, it stores it only and does not send it to any iBGP or eBGP neighbor.