I tried to replicate your results, but I was unable to. What I did was I removed the following command from the BGP configuration of ISP1:
neighbor 192.168.12.2 route-map PREPEND_EU out
…and I replaced it with the following command:
neighbor 192.168.10.10 route-map PREPEND_EU in
The result was that the prepending of the AS’es takes place as the BGP update comes into ISP1, so I see the prepended AS’es within the BGP table of both ISP1 as well as ISP2 as expected. Actually, it took a little bit of time (about 30 seconds) before the BGP table of ISP1 was updated.
You may want to check your configuration again? Let us know how your troubleshooting goes.
When we talk about “well known” communities, we are simply saying that there are four predefined communities in BGP. These are known as:
These are further described in the lesson. They are well-known in the sense that they have built-in commands that you can use to activate them simply because they are used quite often. For example, the No Advertise community can be
Furthermore, RFC1997 describes these well-known communities as those that “have global significance and their operations shall be implemented in any community-attribute-aware BGP speaker.”
BGP communities and extended communities are indeed transitive, however, they are not optional. Even if you configure no community in your implementation, by default, you are using the “Internet” well-known community, which simply advertises the prefix to all BGP neighbors.
For more information on community types and community propagation, take a look at this NetworkLessons Note on BGP community types.
In my lab a single router is acting as ASBR with OSPF on one leg and BGP into other. I am trying to match the Router ID of the router that send OSPF routes and set the community string over BGP, is this technically possible ?
It is possible to create a route map that will set the community string for particular prefixes it sends to its BGP neighbors. This can be done by using the match ip route-source route-map command where the OSPF router ID is the route source.
You can then set the community of those prefixes that are sent from the desired route source (OSPF router ID) to whatever you like.
For more info on setting BGP communities using a route map take a look at this lesson:
For more info on route maps in general, take a look at this lesson:
The route map you have configured matches all prefixes that come from your neighboring OSPF router with ID 188.8.131.52, and assigns the appropriate community to that prefix. However, by applying that route map to the redistribution into BGP, this route map also filters all other OSPF prefixes from being redistributed. Remember that a route map always has an implicit deny-all at the end. You must add a second command entry to the route map to allow everything else to go through, without changing the community. This command would resolve your issue:
I see, you’re talking about the two different types of BGP communities, the standard and extended communities. These are two different ways of representing communities. The standard BGP community is defined by a 32-bit number that can be included with a route within the BGP update. A community is actually an optional transitive attribute.
Now an extended BGP community is simply a redefining of the BGP header that allows a 64-bit number to represent the community rather than a 32-bit number. This simply gives more granularity to the configuration of various attributes. In particular, extended BGP communities provide structure for various classes of information and are very often used for VPN services. The extended communities format is explained in detail in RFC 4360.
Now this should not be confused with a Private BGP community. Private BGP communities follow the convention that the first 16-bits represent the AS of the community origination, and the second 16-bits represent a pattern defined by the originating AS. The private BGP community pattern could vary from organization to organization, do not need to be registered or published. That’s the meaning of the word “private” in the title.
You can find more info about all of these at the following links:
@ReneMolenaar : Thanks for this amazing BGP community explanation which I have had used for troubleshooting. I have a question here.
Is there a possibility for any customer to present with their communities like : and ask to add this is within t he BGP communities.
I have had checked the community examples that you have shared with specific like Prepending/Regional/Local pref
but not able to wrap my head around the customer ASN number for specific customer.
From what I understand, you’re asking if you as a customer can create your own community and share it with the ISP? I’m not sure I understand your question. Can you share a little bit more and clarify so that we can help you further?