On 2010-08-05 14:34, Aleksi Suhonen wrote:
> Hi,
>
> Remi Despres a ecrit:
>>> If this this approach is retained, I could contribute on detailed
>>> changes to RFC 3679, with whoever is interested.
>
> Steven Blake wrote:
>> I agree with this in principle, but there are still a few issues:
>>
>> - If the sending host sets FL=0, and an intermediate router resets it
>> non-zero, the receiving host cannot determine whether the sending host or
>> an intermediate router set the FL. This may break some e2e
>> applications of
>> the FL.
>
> Actually, having had a couple of nights more to sleep thinking
> about this, I have a couple more questions regarding this argument:
>
>
> If the sending host sets FL=0, then the receiving host is clearly
> not even expecting anything special in that field?
>
> If some e2e application is using the FL, it will surely be using some
> signalling method associated with the FL values?
>
> So when a host receives an FL that doesn't match earlier signalling,
> it can determine that it was set by an intermediate node, and that
> the original FL was zero?
That doesn't prevent a case where the intermediate node, for whatever
reason (including MITM), sets a label in the format that does match
the signalling. We don't know what the signalling is like...
>
>
> Is there an internet-draft out there that would answer anything
> other than "yes" to the above questions?
I think this only works if we assign at least one bit in the label
to mean 'e2e or mutable'. And even that is not immune to MITM forgery.
>
> Can it be altered with reasonable effort so that it too would
> yield "yes"es?
I am pessimistic at the moment, which is why I suggested we have
a binary choice.
Brian
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