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Re: (ngtrans) Questions on Configured Tunnel MTU and TOS Byte Settings
Roy,
Roy Brabson wrote:
>
> I've got a few of questions on configured tunnels, as described in
> draft-ietf-ngtrans-mech-v2-01.txt.
...
> - In section 3.5, the TOS byte is defined as being set to 0 unless
> otherwise specified. What exactly does this mean? That, if RFC 2893 is
> followed the DSCP in the TOS byte may be set to a non-zero value? Or
> that RFC 2893 and RFC 3168 should explicitly NOT be implemented for
> configured tunnels? If the latter, I think some discussion on exactly
> WHY these two RFCs are not to be implemented would be helpful.
Firstl there is an important typo in the references. [20] should be
RFC 2983 and *not* 2893. 2983 is the diffserv/tunnels RFC. Although
it's only Informational, I would be very upset if the transition
draft was intended to mean "don't implement 2983". On the contrary,
it should mean "do implement 2983" and if the text isn't clear
on that, it needs fixing.
I don't claim expertise on ECN, but I expect the same applies.
>
> - In section 3.6, the TOS byte of the inner packet is left unmodified at
> the tunnel egress. This seems to contradict some of the referenced.
> For instance, RFC 3168 defines both limited-functionality and
> full-functionality support for ECN support over tunnels. For
> limited-functionality, which seems to most closely match what is
> described in this draft, it discusses what to do at the tunnel egress if
> the CE option is set in the outer packet header but not the inner packet
> header. This processing does not seem to match what is described in
> this draft. Is this intentional?
Surely the interpretation should be the same, i.e. do what [20] and [21]
say. If not, the text needs fixing.
By the way, RFC 2983 is Informational because at the time it was written,
we didn't feel certain enough to put it on standards track. But I've
seen nothing to suggest that what it recommends is wrong.
Brian