Routes learned from eBGP peer are not propagated to iBGP

RouterOS Forwarding Protocols
1

Hello,

Router A and B are different ASes and have eBGP peering in between.
Router B is not advertising the routes learned from A to Router C which is in the same AS with Router B.
Route-reflection does not apply imo because Router A is not an iBGP peer so that its routes can be reflected to Router C.
V 6.15
Can somebody explain how Mikrotik is handling BGP in this scenario?

Thanks

2

Your question has been asked, discussed and answered before … Do a bit of searching on the Forums.

e.g. here is one such thread. http://forum.mikrotik.com/t/bgp-routes-not-propagated-between-ibgp-and-ebgp/75040/1

3

I already did searching in forums, that link you posted is among the open tabs in my web browser. However those are all workarounds for the simples functionality in all other vendors.

Also I did not quite understand your workaround. Are you adding and stripping some arbitrary communities to the routes and trick BGP to treat them as inter-confederation and make it advertise?

Thanks!

4

Btw that link is more about iBGP to eBGP peer. My question is the exact opposite. Routes learned via eBGP is not propogated to the next iBGP peer.

5

To setup iBGP on Mikrotik, there are two settings you have to turn on..
one is “Client to Client Reflection” .. .located under the default bgp instance setting
the 2nd one is under the BGP peer setting “Route Reflect”

Just make sure you are using / not use the acl filters as needed. (default you don’t need to have any filters for iBGP).

As to use of Communities, in the other example, it is nothing more than a ‘tag’, you can use your own set of arbitrary communities to to mark prefixes on the inbound side, and use these marks in the filters on the outgoing side.

We use it do different things… e.g. we use communities to mark prefixes advertised to us from down-stream customers, and we use these communities to build a filter to announce these prefixes to certain upstream… …

6

Take a closer look.. that discussion was about two routers running eBGP to external peers, and iBGP between them..
with Full Route Table being exchanged between them… (so ebgp ↔ Ibgp ↔ ebgp)

7

To setup iBGP on Mikrotik, there are two settings you have to turn on..
one is “Client to Client Reflection” .. .located under the default bgp instance setting
the 2nd one is under the BGP peer setting “Route Reflect”

Your input is appreciated!
Do those need to be turned on both peers? Like both peers are RR servers and RR clients just to be able to achieve a proper iBGP operation?

This solves my issue however what you have written is also the instructions for “how to enable route reflectors”. But I do not want route reflectors, I just want BGP to operate as it does on all other vendors.

Is this how iBGPs supposed to be configured in Mikrotik? Always with route reflectors enabled?

Thanks!

8

If you want routes learned via eBGP to be reflected via iBGP to an iBGP peer, then yes you need to turn on Route Reflection.
In my case, I am taking full routes on both external peers, as such both of them are Route Reflector Server and Client.

Here is a nice article on the differences between iBGP and eBGP http://www.differencebetween.com/difference-between-ebgp-and-vs-ibgp/

You can do a test lab setup to see what is the behavior if MT iBGP setup… I does not require Route Reflection…
However depending on your exact configuration, iBGP route distribution will also get affected by what type of routes are getting redistributed… e.g. see this article …http://rhwiii.info/blog/archives/626

And keep in mind that you may very well need to run another routing protocol (e.g. ospf) if you are needing both routers to be able see each other’s loopback interface.

9

Thanks faisali.
I am aware of the differences between iBGP and eBGP. However Mikrotik seems to be not.
In the link you posted, read the 2nd article in “What is the difference between eBGP and iBGP?”

  1. Routes learned from eBGP peer will be advertised to other peers (BGP or IBGP); however, routes learned from IBGP peer will not be advertised to other IBGP peers.

This is the proper default behaviour that a router should demonstrate WITHOUT route reflector setup. I have setup many BGP scenarios in ISPs with Cisco and redback equipment like this.

Clearly Mikrotik has misinterpreted RFC 2796 because it covers iBGP-to-iBGP advertisements not eBGP-to-iBGP.