From: Carlos G Mendioroz (tron@huapi.ba.ar)
Date: Fri Nov 07 2008 - 17:11:40 ARST
I always thought of RDs as part of the destination network
(global meaning).
The thing about being unique or not should track if the network is the
same or not, and it only matters, AFAIK, if you have the same custommer
network connected somehow to more than one PE.
In that case you want it to be "the same network" for MP-BGP routing
decisions (I guess), and so you need RD to be the same.
In any other case, you need RDs to be different, or else route info
clashing will occur.
-Carlos
Marko Milivojevic @ 6/11/2008 11:37 -0200 dixit:
> On Wed, Nov 5, 2008 at 16:10, Pavel Bykov <slidersv@gmail.com> wrote:
>> As Ivan pointed out, RD is a system significant parameter, meaning it has to
>> be unique on the system only. It is also a mandatory parameter, without
>> which VRF will not function. RT is the domain wide parameter which you need
>> to keep unique. And by domain-wide i mean reeealy wide.
>> Basically RT is the extended community that decides on the VRF.
>
> Well, neither are truly correct, I'm afraid.
>
> RD: It is relevant on the local system in a sense that VRF won't work
> without it. However, it's also a globally significant, as in the
> network running L3VPN's you "can't" have two VPN's sharing the same RD
> and have overlapping addresses. As long as VPN's don't have
> overlapping address space, this doesn't apply, but one should have it
> in mind.
>
> When it comes to RT, it is true that it is used as a sort of a "hint"
> to determine VRF, but in a light of what can be done with RT's, it's a
> gross simplification. You can make certain prefix part of multiple
> VRF's based on RT's, you can restrict prefix from becoming part of
> certain VRF, etc. One thing that is not true about RT is that it needs
> to be unique. Depending on what is that you need to do with certain
> VPN, you will have RT unique per VRF, per box, or per "domain".
>
> One thing that needs to be clear is:
>
> RD: This is a parameter that makes IP address unique and prevents
> address overlap between VPN's.
> RT: This is an extended community that helps determine VPN membership
> of a prefix it's attached to.
>
> Neither need to be unique globally, but RD needs to be unique on each
> box - you can't have multiple VRF's sharing it. You can have multiple
> VRF's on a single box importing and exporting the same RT's.
>
> --
> Marko
> CCIE #18427 (SP)
> My network blog: http://cisco.markom.info/
>
>
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-- Carlos G Mendioroz <tron@huapi.ba.ar> LW7 EQI ArgentinaBlogs and organic groups at http://www.ccie.net
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