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:
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:
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
At 01:32 PM 8/15/02 -0700, Art King wrote:
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" <erosen@xxxxxxxxx>
To: "Shahram Davari" <Shahram_Davari@xxxxxxxxxxxxxx>
Cc: <mpls@xxxxxx>; "Loa Andersson" <loa.andersson@xxxxxxxxx>; "George
Swallow" <swallow@xxxxxxxxx>
Sent: Wednesday, August 14, 2002 11:27 AM
Subject: Re: Encapsulating MPLS in IP or GRE
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.
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