Re: [Softwires] WG LC softwire-lb

[Robert Raszuk <[e-mail]>]

<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.


> Hi Robert,
> 
> Thank you for your comments, please see inline.
> 
> On 4/24/2009 4:31 AM, Robert Raszuk wrote:
>> 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 ?
> 
> 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.
> 
>> * 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 ?
> 
> 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.
> 
> 
> 
>> Cheers,
>> R.
>>
>>
>>> 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
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>