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RS0069 - BGP Route Reflector (Part 3)

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Difficulty Level: 
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The video lays a foundation of building a scalable BGP topology on Cisco router using route-reflectors. We will go through what you need to know about route-reflector rules of route advertisement, both single and dual route-reflector topology, and the significance of a cluster ID. We will also touch on expanding BGP topology even further with route reflector hierarchy.  
 
Part 3 of this video goes over route advertisement characteristics and route reflector hierarchy
 
Topic:
  • Route Reflector - iBGP
    • Cluster ID
  • Route Reflector - eBGP
  • Advertisement Characteristic
  • Route Reflector Hierarchy

About Author

Metha Cheiwanichakorn, CCIE#23585 (RS, Sec, SP), is a Cisco networking enthusiast with years of experience in the industry. He is currently working as a consulting engineer for a Cisco partner. As a founder of and an instructor at labminutes.com, Metha enjoys learning and challenges himself with new Cisco technologies.

7 comments

Hey man,

First off... really great tutorials. The best I've come across for BGP RRs. So thanks so much!!!!

I didn't really quite understand why your BGP session didn't reroute through R3 when your session between R2 and R4 went down. I figure since you peered to Loopbacks that session should have stayed active. Was it because you actually shut down the BGP session versus shutting down the interface?

Thanks Metha

Hi Metha,

Last thing. Any chance we can get the configs wanted to model this in VIRL without all the hand jamming.

thanks again

Hi Metha,

great videos, just using some of these as i'm preparing for CCDE. I've heard about this concept of route deflection with route reflectors, is there something which you have lab videos on (or might make in the near future?)

Cheers,

We are not familiar with the concept and google does not yield much. Do you have any reference doc you can share?

Hi,

An example is presented in the figure below. If R1 receives a packet with destination = d then R1 knowns that the NH for this destination is RR1 and therefore will forward it to R2 since R1 has no direct path to RR1. Once the packet reaches R2 – it knows that the NH for destination d is RR2 and consequently it forwards it back to R1 (and creates a loop) since it doesn’t have a direct physical connection to RR2. This is an example that shows that in order to avoid any loops in the data plane the RRs for IP networks should be in path of the data traffic. For this particular example RFC 2796 - BGP Route Reflection actually warned us that “In addition, when a RR reflects a route, it should not modify the following path attributes: NEXT_HOP, AS_PATH, LOCAL_PREF, and MED. Their modification could potential result in routing loops.”

Hope this link works! https://ibb.co/mMpwo5

After reviewing the diagram, it doesn't appear the iBGP is setup properly. You normally setup iBGP session with RR by following the physical topology. In thie case, R1 and R2 should RR with R1 has iBGP to RR2 and R2 has iBGP to RR1, and R1/R2 has iBGP to each other. Wouldn't that solve the routing loop?

Yes what you describe would solve the deflection, thanks for validating!

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