Subject: LOcally Imported Routes?

From: John Smith <[email-masked]>
Date: Thu, 31 Jul 2003 11:15:16 +0100 (BST)

Dan et. al,

From: "Dan Tappan" <[email-masked]>
 
> Look at it another way. Let's say the configuration is you hypothesize, 
> maybe as below:
>   ip vrf A
>    rd 1:1
>    route-target both 100:100
>   !
>   ip vrf B
>    rd 2:2
>    route-target both 100:100
>    route-target export 100:200
> !

[clipped]
 
> 1:1:x/x,  Label=L1, RT={ 100:100}
> 2:2:x/x, Label=L1, RT={100:100, 100:200}
> 
> will produce exactly the same effect on a remote PE as advertising
> 
> 1:1:x/x, Label=L1, RT={100:100, 100:200}

BUt Robert in one of his previous mails said
 
> Yes this is correct :). Advertising of locally imported routes should
> not be allowed.

This means that we should not advertise RT 100:200

And i happen to concur with Robert on this as AFAIK locally imported or redistributed
routes are not re-advertised by BGP (as said by Robert). 

Regards,
JOhn

________________________________________________________________________
Want to chat instantly with your online friends?  Get the FREE Yahoo!
Messenger http://uk.messenger.yahoo.com/

---

From: Dan Tappan <[email-masked]>
Date: Thu, 31 Jul 2003 08:30:05 -0400

>This means that we should not advertise RT 100:200

That's not what Robert meant. He said one should not re-advertise the route 
which is imported into VRF B. That is not the same as saying that one 
shouldn't give the operator mechanisms to mark routes with the appropriate 
policy. That is, if the route distribution policy that is required to 
support the desired VPN connectivity requires that a route be exported with 
both RT's 100:100 and 100:200, then an implementation should provide a 
mechanism to do so.

Recursive export would be a way to provide that mechanism, but it's a 
pretty crude one, which doesn't solve all problems and is inappropriate in 
some connectivity scenarios. Consider, for example, the case where you have 
3 sites: A, B, C. Both A and C should be able to talk to B, but A and C 
should not communicate directly. Recursive export of routes imported into B 
would break that policy.

Not to mention that applying recursive export blindly would result in an 
explosion of routing information.

So, even if an implementation provided recursive export, it shouldn't be 
the default behavior.