Lokesh,
When you are running OSPF and migrating to
a MPLS services, there are different options for PE-CE routing protocol. If you
want to keep your OSPF transparency, then one has to run OSPF on PE-CE links. If
you are running BGP then you would be exposed to dealing with external /
internal route preference if there is any backdoor connectivity between the
sites.
In the latter case in order to avoid the
backdoor link between two sites to be preferred, either you have to remove the
backdoor or run BGP (or any other instance) so that OSPF route over the
backdoor link becomes also external and could be compared to CE advertised
external route learned over MPLS cloud.
One can conceive that the intelligence for
BGP-OSPF interaction could be put on CE and now CE could run BGP with PE
without impacting OSPF transparency. There are pros and cons to this which I
don’t want to debate here. We published a proposal some time back (although
it was never presented / announced). You can find a link to it at
http://internet-drafts.osmirror.nl/draft-mirtorabi-l3vpn-igp-transparency-00.txt
thanks
Sina
From:
ospf-bounces at ietf.org [mailto:ospf-bounces at ietf.org] On Behalf Of Lokesh Jain
Sent: Friday, March 07, 2008 11:23
AM
To: Acee Lindem
Cc: ospf at ietf.org
Subject: Re: [OSPF] RFC 4577 Query
Hi Acee,
Thanks for the reply. I got your point.
But my doubt still remains.
Are we directly migrating from legacy OSPF backbones to BGP/MPLS VPN Backbone
with OSPF on PE/CE links or earlier BGP was used on PE/CE links?
If BGP was used, then the complexity/procedures of BGP/IGP interaction (special
in this case since we want to redistribute AS-External routes as Inter-area
routes) defined by RFC 4577 would already be in existence. We are just moving
this interaction from CE to PE to save CE from the extra effort and provide
transparency.
Am I correct ?
On Fri, Mar 7, 2008 at 8:23 PM, Acee Lindem <acee at redback.com> wrote:
Hi Lokesh,
On Mar 7, 2008, at 5:16 AM, Lokesh Jain wrote:
> Hi All,
>
> In RFC 4577 it states that earlier PE-CE link used BGP but to
> provide certain advantages to customer, OSPF would be a better
> choice between PE-CE link.
> But to do that we have to modify BGP /OSPF interaction so that
> routes are distributed as inter-area routes and not as AS-External
> routes.
>
> My doubt is:
>
> In earlier scenario, CE would be running an instance of BGP and
> some other IGP, say OSPF. In that case also the routes distributed
> in a customer VPN site would be AS-External routes and not inter-
> area routes. How was that handled in previous case? Or is it the
> just the case of moving BGP/OSPF interaction from CE to PE?
>
> Please guide me regarding this. I must be missing on some point here.
The point is for an ISP to provide a transparent Layer 3 VPN service.
If the CE is forced to handle all the complexity of the BGP/IGP
interaction, this is hardly transparent. RFC 4577 mostly succeeds in
this goal and is widely deployed.
Hope this Helps,
Acee
>
>
> --
> ~~~~~~~~~~~~~
> Thanks & Regards,
> ~~~~~~~~~~~~~
> Lokesh Jain
> Senior Software Engineer,
> Samsung India Software Operations Pvt. Ltd.,
> Bagmane Tech Park,
C V Raman Nagar,
> Bangalore.
> Mob: 9880611348
> -----------------------------------------------------
> You always miss 100% of the chances u don't take
>
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--
~~~~~~~~~~~~~
Thanks & Regards,
~~~~~~~~~~~~~
Lokesh Jain
Senior Software Engineer,
Samsung India Software Operations Pvt. Ltd.,
Bagmane Tech Park,
C V Raman Nagar,
Bangalore.
Mob: 9880611348
-----------------------------------------------------
You always miss 100% of the chances u don't take
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