Re: [rrg] IRON: SEAL summary V2

[Robin Whittle <[e-mail]>]

Hi Fred,

I think my SEAL summary V2 (msg05982) with your comments below is OK
for now.

 - Robin


>> Adapting to changed PMTUs
>> -------------------------
>>
>> I am not sure if or where it is specified, but I understand that SEAL
>> will allow exploration of increased PMTUs.  According to RFC 1191 and
>> therefore RFC 1981, the SH can try sending a longer packet than it
>> has been told to send by a previous PTB, after 10 minutes has elapsed.
> 
> This is discussed in SEAL, Section 4.3.5.



>> Jumboframes
>> -----------
>>
>> "Jumbograms" refer to IPv6 packets with special formats so they can
>> be longer than 2^16 bytes, and can be as long as 4 gigabytes.
>> Neither SEAL, Ivip's IPTM, nor any CES proposal attempts to deal with
>> these.
>>
>> See discussion in msg05979 and msg05981 - Fred writes that SEAL can
>> accommodate jumbograms - but I can't see how.
> 
> The draft talks about jumbograms and cites RFC2675. But,
> it could probably benefit from a sentence or two telling
> how the Jumbo Payload Option is processed.


>> As far as I understand how SEAL would work, SEAL will be able to
>> smoothly adapt to the appearance of jumboframe ~9k byte paths between
>>  ITEs and ETEs.
> 
> Yes.


>> For both IPv4 and IPv6, if the SH ignores PTBs, or if there is some
>> filtering between the ITE and the SH which drops PTBs, then there's
>> no way the SH is going to adapt its packets to the lengths required
>> by SEAL to send them without fragmentation, segmentation or whatever.
>>
>> No CES architecture tries to cope with these problems - they must be
>> fixed directly.
>>
>> As far as I know, SEAL does have "segmentation" capabilities - but
>> these are not intended to be used within the IRON CES architecture.
>> So SEAL's segmentation is no solution to this kind of failure of
>> PMTUD.  There's nothing to be done about this - the fault is in the
>> SH and/or the filtering, so these need to be fixed.
> 
> This discussion is not specific to SEAL nor even to
> tunneling in general. If the SH is not accepting PTBs
> from the gateway that connects the source's site to
> the Internet, then there is a problem regardless of
> the way in which the gateway connects.
> 
> Thanks - Fred
> [e-mail]