Re: MPLS Route Targets

I can do nothing for you if you do not concede that RT's identify the VPN.
(Not the RD). If this is true, you have fallen into a state of Ignorance. I
am sure ANY CCIE-SP will correct you on that point. You claimed you didn't
mind being wrong. I do not believe that is true for 1 second.

I just don't get how you can say you have little experience with Inter AS
VPN and you come out to correct me after I have used and deployed it for
years. I am not saying that I cannot be proven wrong but I know I would be
taking a different approach then you. I guess I could turn it around by
stating:

You show me ONE instance where the RD has to match and I will believe you. I
am tired of proving your statement wrong. You prove it right Sir.

You keep changing your point. I know you don't think so, but EVERYBODY is
watching. I do not have to judge your Instructing skills, everyone else will
be judging you. You have done that to yourself.

Send the dynamips file to me so I can judge for myself concerning your point
that RD's should match.

-- 
Paul Negron
CCIE# 14856 CCSI# 22752
Senior Technical Instructor
www.micronicstraining.com
> From: Carlos G Mendioroz <tron_at_huapi.ba.ar>
> Date: Wed, 25 Aug 2010 06:57:52 -0300
> To: Paul Negron <negron.paul_at_gmail.com>
> Cc: Adrian Brayton <abrayton_at_gmail.com>, Cisco certification
> <ccielab_at_groupstudy.com>
> Subject: Re: MPLS Route Targets
> 
> Paul Negron @ 25/08/2010 0:23 -0300 dixit:
>> All,
>> 
>> I have once again proved that RD's do NOT have to match under ANY
>> conditions.
> 
> Paul,
> I don't disagree with this. Even if they don't match, selection of path
> will be carried on by BGP policy.
> 
> Let's put this straight, i.e., what I'm saying here:
> 
> (1) RDs are to enable MP-BGP to carry multiple sets of routes without
> mixing them.
> 
> (2) As long as two routes have a different RD, BGP will not try to get
> the best one, it will just keep them both as different routes
> 
> (3) I was under the impresion that the selection of the route to be
> imported into a vrf could be carried out by a different mechanism, when
> in fact it is not.
> 
> (4) Nevertheless, route behaviour may be forced different in certain
> cases depending on RDs being the same or not the same.
> 
>> 
>> I would like to explain it this way.
>> 
>> You want to think of the RD's as BGP's way of seeing an interface. Since
>> EVERY prefix that leaves the interface will receive the very same RD, this
>> allows BGP to maintain separation from other interfaces that apply a
>> different RD. 
>> 
>> (This is not how it exactly works in the above sentence, it is just a better
>> visual)
> 
> Hmmm.
> 
>> 
>> They are treated like different prefixes between RD's while the route is a
>> VPNv4 route (96 bit address).
> 
> Right.
> 
>> 
>> Once the prefix terminates to the other side, the routes moving from one
>> direction have nothing to do with the routes moving in the other direction
>> in BGP, only that they don't overlap with all 96 bits (tunnels are
>> unidirectional). That is why it is important that the RD not identify the
>> VPN. The Route-Targets do. When they are imported, they are seen as existing
>> in 2 different RD structures at the same time.
> 
> Oops. This is one way of using the scheme.
> But BGP certainly does not create tunnels by default. This is a
> consequence of creating different RDs for every VRF instance at every
> different PE.
> 
> And RTs do not identify in the sense of identity. They are tags to
> recognize which routes you are be interested in from the others.
> RDs on the other hand, are part of the identity, that's why different
> RDs do not mix!
> 
>> 
>> Even if the the same route comes from 2 different PE routers with 2
>> different RD's configured, they are still viewed by BGP as 2 different sets
>> of prefixes that need to kept separate throughout the BGP domain. However,
>> BGP attributes will be sent across this tunnel from one CE to the other. You
> 
> This is key to our difference here: You say "even", I say "only".
> It seems like you refuse to consider what happens in the case where you
> assign the same RD to two different VRF instances!
> 
> (5) All I'm saying is that if RDs are the same, a network in both VRFs
> will be considered *the same network* by BGP even before reaching the
> final PE and thus BGP route selection policy will take place even in
> transit.
> 
> (6) That being the case, the selection might be based on a different
> policy, because it might take place at a different router.
> 
>> I Have the final configuration in Dynamips that proves this and will gladly
>> unicast it to anyone who asks. You can test the attribute theory by shutting
>> down the primary link.
> 
> And I have the dynamips (actually dynagen) file that proves this too.
> 
>> 
>> I have already given Carlos his complimentary copy for his role in helping
>> with the discussion.
>> 
>> Paul
> 
> Thank you Paul, but what happened here is that we, I guess, were talking
> about different things.
> I do disagree though in that part where you say I was talking nonsense :(
> 
> -Carlos
> 
> -- 
> Carlos G Mendioroz  <tron_at_huapi.ba.ar>  LW7 EQI  Argentina
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