Redundant Routes, BGP with MPLS provider

Matthew Petach mpetach at
Sat Sep 1 23:22:48 UTC 2012

On Fri, Aug 31, 2012 at 9:21 AM,  <Bill.Ingrum at> wrote:
> I think having a GRE tunnel for the internal routing protocol is
> unnecessary.  Can you explain the reasoning behind this?  I understand
> the technical issue whereby GRE will allow multicast for EIGRP, OSPF,
> etc, but why not just redistribute into BGP?
> I work on a lot of MPLS CE routers, and in general you can accomplish
> anything you need by redistributing your internal routing protocol into
> BGP, and adjusting LP, MED and AS Prepend as needed.
> Thanks,
> Bill

So, rather than run an IGP between siteA and siteZ across
a GRE tunnel, you'd prefer to redistribute your IGP into BGP
at siteA, advertise those routes upstream...and at siteZ, accept
the routes in via BGP, and then redistribute them into the IGP
for the other routers at siteZ, and vice versa?

Or would you have every router at siteA and siteZ participate
in BGP, so that all the routers at siteZ get the routes from
siteA intact?

(choice B tends to have practical implications on what
network gear you can run within the sites; many devices
that will happily speak OSPF or EIGRP won't be quite so
happy participating in an iBGP mesh.  And choice A...well,
I think we all know the pitfall with choice A, so enough said
on that score).

Curious to hear the actual mechanism you'd use to make
this work in the real world.



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