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[MPLS-OPS]: Re: Advertising Routes learnt from PE to PE

  • From: Aamer Akhter <aakhter@cisco.com>
  • Date: Wed, 14 May 2003 14:44:12 -0400
  • CC: <mpls@UU.NET>
  • User-Agent: Microsoft-Entourage/10.1.1.2418

On 5/14/03 1:58 PM, "Spice Sylvia" <falsesylvia@yahoo.co.uk> wrote:

> Hello Aamer,
> 
> Why would the "rd" have changed?

|--------1
HUBCE    HUBPE
|--------2

Suppose the sites prefixes are sent to the HUBPE, which advertises to HUBCE
over link 2 (lets' call this vrf2), the HUBCE advertises this back to the
HUBPE over link 1 (vrf1). vrf2 and vrf1 will have different rd's because
they are different vrfs.

> 
> Is this a new feature?
> 
> How does changing RD help?
> 
> 
> Aamer Akhter <aakhter@cisco.com> wrote:
> On 5/14/03 10:51 AM, "Ferit Yegenoglu" wrote:
> 
>> 
>> Sylvia,
>> 
>> One possible scenario where this could happen is the hub-spoke BGP/MPLS
>> VPN. In this case the spoke PEs advertise their routes with a Route
>> Target value "Hub". The hub PE imports these routes and advertises them
>> to the CE router in the hub site. These routes are advertised across the
>> hub site and eventually back to the PE hub router via a different
>> interface. The PE hub router then readvertises these routes to the spoke
>> PEs with a Route Target value "Spoke" and a different VPN label.
> 
> But to BGP, these "readvertised" prefixes are not the same. The rd will have
> changed.
> 
>> 
>> Ferit
>> 
>> 
>> 
>>> -----Original Message-----
>>> From: owner-mpls@UU.NET [mailto:owner-mpls@UU.NET] On Behalf Of Sugar,
>>> Sylvia
>>> Sent: Wednesday, May 14, 2003 10:07 AM
>>> To: mpls-ops@mplsrc.com
>>> Cc: mpls@UU.NET
>>> Subject: Advertising Routes learnt from PE to PE
>>> 
>>> Hi,
>>> WIll a PE router ever advertise a route it learns from another PE
>> router
>>> to some other PE router.
>>> I dont think it will ever do that as all the PE routers are IBGP peers
>> and
>>> would generally be in
>>> full mesh.
>>> 
>>> Is there any case when this might happen .. i.e. a PE router
>> advertises a
>>> Route learnt from one PE
>>> to another PE. How can one do that .. because IMHO the label that will
>> be
>>> advertised by the former
>>> PE router will be for the PE router to which he sends the UPDATE. How
>> can
>>> this PE router advertise
>>> another PE router the same label?
>>> 
>>> Moreover, if for some reason he has to .. does he assign a new label
>> and
>>> then advertise?
>>> 
>>> ANy comments on this would be very helpful!
>>> 
>>> Silviya Sugar
>>> 
>>> __________________________________________________
>>> Yahoo! Plus
>>> For a better Internet experience
>>> http://www.yahoo.co.uk/btoffer
>> 

-- 
Aamer Akhter / aa@cisco.com
NSITE - cisco Systems