nanog mailing list archives

Re: iMPLS benefit


From: Enke Chen <enke () redback com>
Date: Mon, 22 Mar 2004 18:22:01 -0800


Hi, Mark:

Message-ID: <405F05D9.1080301 () cisco com>
Date: Mon, 22 Mar 2004 16:27:21 +0100
From: "W. Mark Townsley" <townsley () cisco com>
To: Enke Chen <enke () redback com>
Cc: David Meyer <dmm () 1-4-5 net>, Yakov Rekhter <yakov () juniper net>,
      sonet twister <sonet1010 () yahoo com>, nanog () merit edu
Subject: Re: iMPLS benefit
References: <20040319220615.A245D15D3C4 () popserv1 redback com>


Enke Chen wrote:

Hi, Mark:
I was no vacation and just became aware of this thread. 

Lucky you!

 > I have some clarifications here:

(1) The relevant implementation is "Encapsulating MPLS in IP or Generic
Routing Encapsulation (GRE)" for L3VPN (draft-ietf-mpls-in-ip-or-gre-xx.txt)

This draft describes encapsulation and decapsulation of MPLS over IP, MPLS over 
GRE (with and without optional GRE fields), and (in more recent versions) 
touches on all of these encapsulation modes in the presence of IPsec. There is 
no detail on dynamic establishment of GRE tunnels here.

I should have mentioned the draft "Use of PE-PE GRE or IP in RFC2547 VPNs"
(draft-ietf-l3vpn-gre-ip-2547-xx.txt), in which the notion of dynamic
GRE tunnel is defined:

-----------------------------------------------------------------------
6.1. MPLS-in-IP/MPLS-in-GRE Encapsulation by Ingress PE

   [...]

   The effect is to dynamically create an IP (or GRE) tunnel between the
   ingress and egress PE routers. No apriori configuration of the remote
   tunnel endpoints is needed. Note that these tunnels are NOT IGP-
   visible links, and routing adjacencies are not supported across these
   tunnel.  Note also that the set of remote tunnel endpoints is NOT
   known in advance, but is learned dynamically via the BGP distribution
   of VPN-IP routes.
------------------------------------------------------------------------

Regards,

-- Enke


(2) Redback's implementation does not require manual configuration of
    and GRE tunnels in this case. We have tested the interoprability
    with another implementation that does require manual configuration.

I don't doubt that this can be made to work. However, there are out-of-band 
assumptions here beyond simple support for "MPLS over GRE" which was my initial 
point. e.g., in order to interoperate, a "soft" GRE tunnel node must make 
assumptions that every node it is sending a GRE encapsulated MPLS packet to is 
either (1) manually configured to accept MPLS over GRE from that endpoint, or 
(2) is a PE which is participating in the same "soft" GRE system, learning 
endpoints from BGP updates or some other method. This is, of course, made easier 
when nodes are simply configured to allow MPLS over GRE/IP from any source IP 
address, but this also substantially increases the spoofing concerns for MPLS 
over GRE/IP at that node.

IMHO, if an implementation is going to be made to dynamically learn the 
destination address for an MPLS over IP enabled endpoint from BGP, including an 
attribute to explicitly identify the ability to receive said MPLS over IP 
packets goes a long way to overcome blackhole situations where one could end up 
sending tunneled packets to a PE which isn't able to receive and process them 
correctly.

Thanks,

- Mark


Regards,

-- Enke

* From: W. Mark Townsley
* Date: Mon Mar 15 13:19:37 2004

Please see inline.


Yakov Rekhter wrote:


-------------------------------------------------------

Mark,

i heard there is a way to run MPLS for layer3 VPN(2547)
service without needing to run label switching in the
core(LDP/TDP/RSVP) but straight IP (aka iMPLS).

  ftp://ftp.ietf.org/internet-drafts/draft-townsley-l2tpv3-mpls-01.txt

  See also Mark's talk from the last NANOG

  http://nanog.org/mtg-0402/townsley.html

That requires to run L2TP. An alternative is to run GRE (or even plain
IP). The latter (GRE) is implemented by quite a few vendors (and is
known to be interoperable among multiple vendors).

The only multi-vendor interoperable mode of GRE that I am aware of requires
manual provisioning of point-to-point GRE tunnels between MPLS networks
and to each and every IP-only reachable PE.


I guess you are *not* aware of the Redback implementation of 2547
over GRE, as this implementation is (a) available today, (b)
interoperable with other implementations of 2547 over GRE, and (c)
does *not* require manual provisioning of point-to-point GRE tunnels
between MPLS networks and to each and every IP-only reachable PE.

And, just for the record, (stating the obvious) I don't work for Redback.

------------------------------------------------------------------------

Are you referring to draft-raggarwa-ppvpn-tunnel-encap-sig-03.txt?
(Just guessing as the principal author used to work for Redback).
Thanks for the update, I was in fact not aware that companies other
than Redback had implemented it. You didn't name those companies, but
I will happily stand corrected here.

In any case, the point I was trying to make was that there is more than
one way to do "MPLS over GRE" and that they are not all necessarily
interoperable as you seemed to imply in your message. You have helped
to make that quite clear.

The BGP extension defined in the draft below allows "iMPLS" for 2547 VPN
support without requiring any manually provisioned tunnels (and works for
"mGRE" or L2TPv3).

http://www.watersprings.org/pub/id/draft-nalawade-kapoor-tunnel-safi-01.txt

The question to ask is whether the extension you mentioned above is
truly necessary for supporting 2547 over GRE. The Redback implementation
I mentioned above is an existence proof that the extension is *not*
necessary for 2547 over GRE that does *not* involve manually provisioned
GRE tunnels.

[clip]

- Mark





Current thread: