Subject: RE: Encapsulating MPLS in IP or GRE

From: Shahram Davari <[email-masked]>
Date: Wed, 14 Aug 2002 10:38:43 -0700

Eric,

It is odd to do MPLS-in-GRE over IP, because in this case you are already assuming that there is IP connectivity between the PEs. So why bother to have an extra GRE header, which does nothing, just do MPLS-in-IP. In other words how can you have a GRE-IP tunnel and not
be able to have IP tunnel?

Yours,
-Shahram 

> -----Original Message-----
> From: Eric Rosen [mailto:[email-masked]]
> Sent: Wednesday, August 14, 2002 12:48 PM
> To: [email-masked]; Loa Andersson; George Swallow
> Subject: Encapsulating MPLS in IP or GRE
> 
> 
> In support of work going on in  PPVPN and PWE3, it is 
> desirable to have some
> standards for encapsulating MPLS packets inside IP packets.  
> The draft whose
> announcement  I attach  below is  the result  of merging  two 
>  previous (but
> expired)  documents, draft-worster-mpls-in-ip,  and 
> draft-rekhter-mpls-over-
> gre.  I would like to present this for the consideration of 
> the MPLS WG as a
> standards track document.
> 
>

---

From: Eric Rosen <[email-masked]>
Date: Wed, 14 Aug 2002 14:27:36 -0400

In some  cases you  might already have  a GRE  tunnel through which  you are
supporting a routing adjacency.  It should be possible to send MPLS packets,
as  well  as  IP  packets,  through  such  tunnels,  and  this  requires  an
MPLS-in-GRE encapsulation. 

There are also  other cases in which GRE tunnels (as  opposed to IP tunnels)
are  commonly used,  and you  should be  able to  send MPLS  packets through
them.

---

From: Art King <[email-masked]>
Date: Thu, 15 Aug 2002 13:32:23 -0700

Connecting MPLS VPN PE's over non-MPLS core in a Carrier is a
good example case for GRE usage.

----- Original Message -----
From: "Eric Rosen" <[email-masked]>
To: "Shahram Davari" <[email-masked]>
Cc: <[email-masked]>; "Loa Andersson" <[email-masked]>; "George
Swallow" <[email-masked]>
Sent: Wednesday, August 14, 2002 11:27 AM
Subject: Re: Encapsulating MPLS in IP or GRE

---

From: Mark Duffy <[email-masked]>
Date: Thu, 15 Aug 2002 19:01:30 -0400

Hi Art, are you suggesting that there is something about the MPLS VPN case
in particular that favors mpls-in-gre over mpls-in-ip?  If so would you
explain that?

Thanks, Mark

---

From: Art King <[email-masked]>
Date: Thu, 15 Aug 2002 22:03:07 -0700

Mark,

I've seen a number of configurations where ISP's have merged and have broken
AS's because pieces of the original backbone have been removed in order to
reduce duplicate costs on same route and no one has time/skill to go back
and rebuild/renumber the original network(s). This required BGP to be
tunneled via GRE between dis-contiguous chunks of the same AS. For this
provider topology, tunneling MPLS traffic and MP-BGP over same GRE tunnel
achieves some level of transparency. It's kind of a corner case.

Thanks,

Art
----- Original Message -----
From: "Mark Duffy" <[email-masked]>
To: "Art King" <[email-masked]>
Cc: <[email-masked]>
Sent: Thursday, August 15, 2002 4:01 PM
Subject: Re: Encapsulating MPLS in IP or GRE

> >> In some  cases you  might already have  a GRE  tunnel through which
you
> >are
> >> as  well  as  IP  packets,  through  such  tunnels,  and  this
requires
> >an

---

From: Chris Chase <[email-masked]>
Date: Wed, 28 Aug 2002 11:30:11 -0400

This is the usage I find the most attractive.  

Actually, we had a customer who wanted to do carrier's carrier to create 
their own VPNs for their tenants.  The approach taken was to use GRE 
tunnels.  The customer did not like having to create numerous tunnel 
interfaces.

Mark Duffy wrote:

>>>In some  cases you  might already have  a GRE  tunnel through which  you
>>>      
>>>
>>are
>>    
>>
>>>supporting a routing adjacency.  It should be possible to send MPLS
>>>      
>>>
>>packets,
>>    
>>
>>>as  well  as  IP  packets,  through  such  tunnels,  and  this  requires
>>>      
>>>
>>an
>>    
>>
>>>There are also  other cases in which GRE tunnels (as  opposed to IP
>>>      
>>>
>>tunnels)
>>    
>>
>>>are  commonly used,  and you  should be  able to  send MPLS  packets
>>>      
>>>
>>through
>>    
>>
>>>them.
>>>
>>>      
>>>

---

From: Chris Chase <[email-masked]>
Date: Wed, 28 Aug 2002 12:51:36 -0400

Oops.  Sent before I was done.

In the approach described in

http://www.ietf.org/internet-drafts/draft-ietf-ppvpn-gre-ip-2547-01.txt

the tunnels between PE pairs are dynamic.  No tunnel configuration 
required.  In fact an implementation might chose to not even need to 
create a "tunnel" inteface if the tunnel header is viewed as an outbound 
encapsulation for a given BGP next hop.  Much like there is no 
"interface" created for downstream label switching when using MPLS as 
the tunneling method between PEs.

One descrepancy I see between the the dynamic approach of the above 
draft and
draft-rosen-mpls-in-ip-or-gre-00.txt is the latter requires MTU path 
discovery for each "tunnel" destination.  A static configured MTU or min 
MTU learned over the history of dynamic tunnels used would be prefered.

In the customer's case mentioned below, by using the GRE tunnels made 
the customers creation of hierarchical VPNs (carrier's carrier) 
completely transparent to our service offer.  They could use the 
existing service as defined without ordering or configuring anything 
special in our service network.  Specifically, we did not have to 
certify, deploy, provision and support MPLS CE-to-PE.  Instead it looks 
just like our standard IP service interface definition.

Another application, perhaps less important, in the VPLS context when 
using BGP discovery and MAC address learning is that you do not need a 
label that is upstream PE specific (the label block method).  You know 
which upstream PE sent the packet from the source address of the tunnel.

Chris

Chris Chase wrote:

> Actually, we had a customer who wanted to do carrier's carrier to 
> create their own VPNs for their tenants.  The approach taken was to 
> use GRE tunnels.  The customer did not like having to create numerous 
> tunnel interfaces.
>
>
> Mark Duffy wrote:
>

---

From: Mark Duffy <[email-masked]>
Date: Thu, 29 Aug 2002 11:20:29 -0400

Hi Chris,

If I understand you correctly, you are talking about providing IP
connectivity (only) to a reseller who places their own PE boxes outside
your network and then sells 2547-type VPN services to their customers.  Is
that right?  If so I don't see why it should matter if they use mpls-in-ip
or mpls-in-gre.  Either way achieves the ability to run over a non-mpls IP
backbone.

--Mark

---

From: Chris Chase <[email-masked]>
Date: Thu, 29 Aug 2002 17:48:34 -0400

Yes that is what the customer was trying to do.  I didn't mean to imply 
that IP versus GRE encap mattered.  It didn't matter.

The difficulty for the customer is that their router implementation 
required explicit configuration of an interface for every tunnel.  They 
found that having to create a full mesh of tunnel interfaces was not 
acceptable.  They were ideally suited to the dynamic tunneling mentioned 
in draft-ietf-ppvpn-gre-ip-2547-01.txt

Chris