Re: [Int-area] Discussion about Section 6.1 in draft-ietf-intarea-frag-fragile

Joe Touch <touch@strayalpha.com> Thu, 12 September 2019 14:22 UTC

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From: Joe Touch <touch@strayalpha.com>
In-Reply-To: <7c173abd36fe4307b7d49b345eaa7bb3@boeing.com>
Date: Thu, 12 Sep 2019 07:22:25 -0700
Cc: Brian E Carpenter <brian.e.carpenter@gmail.com>, Bob Hinden <bob.hinden@gmail.com>, "int-area@ietf.org" <int-area@ietf.org>, Suresh Krishnan <suresh@kaloom.com>
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To: "Templin (US), Fred L" <Fred.L.Templin@boeing.com>
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Subject: Re: [Int-area] Discussion about Section 6.1 in draft-ietf-intarea-frag-fragile
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> On Sep 12, 2019, at 6:57 AM, Templin (US), Fred L <Fred.L.Templin@boeing.com> wrote:
> 
>>> IPv4 with a small PMTU also comes to mind, as discussed in Section 3.2.2 of RFC 4213:
>>> 
>>>   In this case, the IPv6 layer has to "see" a link
>>>   layer with an MTU of 1280 bytes and the encapsulator has to use IPv4
>>>   fragmentation in order to forward the 1280 byte IPv6 packets.
>> 
>> Yes, IP fragmentation - exactly.
> 
> See also Section 7 of RFC2473.

There are a number of issues with that RFC, as noted in intarea-tunnels.

E.g., it won’t properly do what you say for IPv4 DF=0 (i.e., treat the tunnel as a true link layer by allowing frag at the tunnel header), nor will it correctly interconnect two hosts for packets with TTL/hopcounts fo 0 (which should work - only routers should decrement those).

Joe