Re: [Tofoo] VXLAN (UDP tunnel protocols) and non-zero checksums

Tom Herbert <therbert@google.com> Fri, 02 May 2014 21:34 UTC

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Date: Fri, 2 May 2014 14:34:25 -0700
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From: Tom Herbert <therbert@google.com>
To: Joe Touch <touch@isi.edu>
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Subject: Re: [Tofoo] VXLAN (UDP tunnel protocols) and non-zero checksums
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On Thu, May 1, 2014 at 2:08 PM, Joe Touch <touch@isi.edu>; wrote:

>
>
> On 5/1/2014 2:00 PM, Tom Herbert wrote:
> ...
>
>      Receiver processing is simple:
>>
>>              - if the checksum is zero, ignore
>>
>>              - if the checksum is NOT zero, it MUST match
>>
>> This is true with caveat that an implementation MAY ignore a zero
>> checksum, not MUST ignore a zero checksum. This is specified in RFC1122.
>>
>
> It says that the app MAY optionally be able to configure the system to
> pass zero-checksum UDP packets up or discard them.
>
> I.e., a *configuration* MAY decide to accept or drop zero-checksum UDP
> packets; the UDP layer isn't in control of that by itself.
>
>
>    VXLAN draft also breaks this by making accepting packets with zero
>> checksums a MUST.
>>
>
> That's not "breaking" anything; VXLAN is - to UDP - an application.
>
> Perhaps not, but making it a MUST in the encapsulation protocol definition
to always accept UDP packets with zero checksums seems a bit austere. For
instance, if I know within my deployment that all senders are configured to
use checksums, then receiving a packet with zero checksum should be
considered an invalid packet.

Tom

Joe
>