Subject: [Softwires] WG LC softwire-lb

From: David Ward <[email-masked]>
Date: Thu, 23 Apr 2009 16:07:19 -0500

All -
	Following the last IETF meeting all comments have been addressed in:

http://tools.ietf.org/html/draft-ietf-softwire-lb-02

The authors have requested a WG LC and I have added L3VPN and PWE3  
that may be interested and have comments on the technology. Please  
send back all comments by May 7, 2009.

Thanks

DWard, Alain

---

From: Robert Raszuk <[email-masked]>
Date: Fri, 24 Apr 2009 01:31:41 -0700

Hi David,

Perhaps I may have missed the discussion on this in the other WGs but I 
have two comments/questions ...

* Why the decision on enhancing the load balancing capability of IP 
encapsulated packet has to be signaled as opposed to be a local matter 
of the ingress router performing encapsulation ?

* Reg use of GRE key for the purpose of load balancing I must say that 
GRE key has already been proposed in number of solutions today. Therefor 
overloading more on it may be impractical. Did authors analyzed use of 
Sequence Numbers in GRE header instead for the purpose of increasing 
effectiveness of load-balancing by the transit nodes ?

Cheers,
R.

> The authors have requested a WG LC and I have added L3VPN and PWE3 that 
> may be interested and have comments on the technology. Please send back 
> all comments by May 7, 2009.
> 
> Thanks
> 
> DWard, Alain

---

From: Carlos Pignataro <[email-masked]>
Date: Wed, 29 Apr 2009 11:23:36 -0400

Hi Robert,

Thank you for your comments, please see inline.

> of the ingress router performing encapsulation ?

This is because the load-balancing field is signaled (see RFC5512), so
using for lb it needs signaling of a block to avoid collisions. Note
also the context from the title, lb for Mesh Softwires. For the L2TPv3
case, and from <http://tools.ietf.org/html/rfc5512#section-4.1>, the
only encapsulating header field that is always there is the Session ID
(Cookie is optional), which is signaled; the case for GRE is equivalent,
but also please see below. If it's only a local matter, the
encapsulating header's fields could not be used and you would be limited
to playing with e.g., the source IP address.

> effectiveness of load-balancing by the transit nodes ?

Yes, it was considered, but we need a field that can be used for flow
identification. From RFC2890, the seq # MUST be used by the receiver to
establish packet transmission order, so it's incompatible with a
per-flow use. The GRE Key's semantics from RFC2890 match this use,
<http://tools.ietf.org/html/rfc2890#section-2.1>:

   The Key field contains a four octet number which was inserted by the
   encapsulator. The actual method by which this Key is obtained is
   beyond the scope of the document. The Key field is intended to be
   used for identifying an individual traffic flow within a tunnel.

Thanks,

-- Carlos.

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---

From: Robert Raszuk <[email-masked]>
Date: Wed, 29 Apr 2009 11:40:21 -0700

<trimming a bit the spam list :)>

Hi Carlos,

Perhaps I was not very clear in the question. I understand that you are 
adding the ability for ingress where for L2TPv3 over IP - Session ID & 
for GRE - GRE key are distributed per egress as per RFC5512.

This is great !

But what I was mainly asking about was the case where egress does not 
signal GRE key. Per 5512 is seems very well allowed as key is optional:

    "Note that the key is optional.  Unless a key value is being
     advertised, the GRE encapsulation sub-TLV MUST NOT be present."

Then if one would read carefully your draft is says there:

    "Needless to say, if an egress router does not support load balancing
    block sub-TLV, the Softwire continues to operate with a single load
    balancing field that all ingress routers encapsulate with."

But since the whole purpose is to provide some additional field in the 
IP encapsulation header other then play with src address for core 
routers doing ECMP shouldn't we mention some text allowing for local 
ingress PE injection of random keys when such a keys are not required by 
  application using 5512 for it's mesh tunnel setup ?

As to my second question I agree. In fact your proposal allows for sort 
of overloading the GRE key semantics to serve both for given application 
as well as for core load-balancing.

Many thx,
R.