Subject: [OSPF] RFC 4577 Query

From: "Lokesh Jain" <[email-masked]>
Date: Fri, 7 Mar 2008 15:46:25 +0530

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.

-- 
~~~~~~~~~~~~~
Thanks & Regards,
~~~~~~~~~~~~~
Lokesh Jain
Senior Software Engineer,
Samsung India Software Operations Pvt. Ltd.,
Bagmane Tech Park, C V Raman Nagar,
Bangalore.
Mob: 9880611348
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---

From: Acee Lindem <[email-masked]>
Date: Fri, 7 Mar 2008 09:53:06 -0500

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?
>

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

---

From: "Lokesh Jain" <[email-masked]>
Date: Sat, 8 Mar 2008 00:53:21 +0530

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 ?

---

From: "Sina Mirtorabi" <[email-masked]>
Date: Fri, 7 Mar 2008 13:57:59 -0800

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-transparenc
y-00.txt

thanks

Sina

________________________________

From: [email-masked] [mailto:[email-masked]] On Behalf Of
Lokesh Jain
Sent: Friday, March 07, 2008 11:23 AM
To: Acee Lindem
Cc: [email-masked]
Subject: Re: [OSPF] RFC 4577 Query

Hi Acee, 

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 ?

Hi Lokesh,

Hope this Helps,
Acee

---

From: Acee Lindem <[email-masked]>
Date: Fri, 7 Mar 2008 16:26:56 -0500

Hi Lokesh,
This is probably a question for the L3VPN WG :^) However, my  
understanding is that this is targeted at migration from an OSPF  
network using dedicated links (not over a VPN). The brief discussion  
of BGP/OSPF in the CE is in comparison to RFC 4577.
Thanks,
Acee
On Mar 7, 2008, at 2:23 PM, Lokesh Jain wrote:

> 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 ?
>