Some other observations: RFC4301 still recommends that it is acceptable to clear the DF bit (sec 5.1.2.1), although it does so in the process of tunneling. That tunneling is (IMO) already covered in RFC2003, which (in sec 3.1) prohibits such behavior. Those cases are important to note, and to note that tunnels - of any kind - are a particularly vexing case as a result. See RFC4459 for more info.
The document doesn't consider the implications of trying to avoid
fragmentation. There are three choices, all of which should be addressed:
1) use conventional path-MTU that relies on NACKs
(discussed)
2) use the updated version of path-MTU (pmtud I-D)
(not discussed)
3) send the smallest possible segment (68 bytes, as per RFC791)
however, as per 4459, it's impossible to send that over
a tunnel and not potentially need to fragment it
It's also worth noting - as others pointed out - that this is
IPv4-specific, and that IPv6's prohibition of in-network fragmentation
doesn't solve the problem (notably because a tunnel acts as an endpoint
for its encapsulated packets, so tunnels remain a problem).
I'm not sure this covers all known problems, but it'd be nice to have
something more definitive on the issue rather than 'yet another document
to put in a roadmap on MTU issues'.
Joe
Jari Arkko wrote:
> FYI.
>
> The IESG wrote:
>> The IESG has received a request from an individual submitter to consider
>> the following document:
>>
>> - 'Fragmentation Considered Very Harmful '
>> <draft-heffner-frag-harmful-02.txt> as an Informational RFC
>>
>> The IESG plans to make a decision in the next few weeks, and solicits
>> final comments on this action. Please send any comments to the
>> [email protected] or [email protected] mailing lists by 2006-11-17.
>>
>> The file can be obtained via
>> http://www.ietf.org/internet-drafts/draft-heffner-frag-harmful-02.txt
>>
>>
>> _______________________________________________
>> IETF-Announce mailing list
>> [email protected]
>> https://www1.ietf.org/mailman/listinfo/ietf-announce
>>
>>
>>
>
>
> _______________________________________________
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