Route learned over iBGP advertised over another iBGP.

[Pasquale Di Dio]

Hi everyone.

I want to report this "strange case" to your attention.

I have 4 BGP Router connected into ring topology in iBGP session.  (and eBGP session to another AS each one)

• Router1 and Router2 send the eBGP routing entry learned to the other router and viceversa. 
  
• Router2 (that already have Router 1 entry) and Router3 share their routing entry one to another; Router2 advertise also the Router1 entry to Router3.

But Over an iBGP session, a router advertises only its best routes learned over eBGP sessions.

A route learned over an iBGP session is never advertised over another iBGP session.

 When a BGP speaker receives an UPDATE message from an internal peer,
   the receiving BGP speaker SHALL NOT re-distribute the routing
   information contained in that UPDATE message to other internal peers
   (unless the speaker acts as a BGP Route Reflector [RFC2796]).

RFC BGP - Send Update Process 

I checked the "BGPRouting::updateSendProcess" method line 402 of this BGRRouting.cc on github 

 if ((_BGPSessions[sessionIndex]->getType() == IGP && (elem).second->getType() == EGP) ||

          _BGPSessions[sessionIndex]->getType() == EGP ||

          type == ROUTE_DESTINATION_CHANGED ||

          type == NEW_SESSION_ESTABLISHED)                <-------------------------------

Router2 decide to send learned entry from Router1 to Router3 because of this line.

Correctly not sended for this other query into the first if:

((elem).first == sessionIndex && type != NEW_SESSION_ESTABLISHED) ||

(type == NEW_SESSION_ESTABLISHED && (elem).first != sessionIndex) ||

I cannot "delete" the type == NEW_SESSION_ESTABLISHED because otherwise it will not send the query, and other EBGP session will not receive the entry.

Some ideas to fix it?

thx