[c-nsp] mpls route target export question

[Kenny Sallee]

Here's my interpretation / explanation: In order to get a route into a VRF
there needs to be some type of tag the router can use to determine which
routes to import into a particular VRF.  This is done with route-target
export command.  In a particular vrf you'd route-target import what was
exported from other vrf's.  So it's the identifier that allows the router to
import whatever routes you want in the route-table of a particular VRF.
 Another way to say it: what is 'exported' from one VRF is a BGP extended
community that is sent by BGP in updates to other PE routers.  The other PE
routers use the extended community as that 'tag' for import into VRF's (or
not - depending on how the RT import is configured).

I believe the route-target exported needs to be unique across the entire
routing domain (else you could have one customer import other customers
routes).  RD can be different per PE router - but I'm not sure why anyone
would want to do that.  If if someone does - can you share thoughts on that?

See here: http://www.ciscopress.com/articles/article.asp?p=28259&seqNum=5
http://ciscodreamer.blogspot.com/2009/08/vrf-route-target.html
and for night night reading:
<http://ciscodreamer.blogspot.com/2009/08/vrf-route-target.html>

On Wed, Aug 4, 2010 at 7:03 PM, Michael Sprouffske <msprouffske at yahoo.com>wrote:

> I'm having a hard time grasping, just exactly what the export feature
> does.  From what I see, the import command basically tells the vrf which
> routes to let into the table.  Can any body give me a answer as to what the
> export route target feature really does in a large network?
>
>
>
>
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