Re: [Rtg-dt-encap-considerations] [nvo3] Alignment and Ethernet encapsulation

Joe Touch <touch@isi.edu> Tue, 20 September 2016 17:08 UTC

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To: Tom Herbert <tom@herbertland.com>, "nvo3@ietf.org" <nvo3@ietf.org>, "rtg-dt-encap-considerations@ietf.org" <rtg-dt-encap-considerations@ietf.org>, Sowmini Varadhan <sowmini.varadhan@oracle.com>
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From: Joe Touch <touch@isi.edu>
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Date: Tue, 20 Sep 2016 10:07:27 -0700
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Subject: Re: [Rtg-dt-encap-considerations] [nvo3] Alignment and Ethernet encapsulation
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Hi, Tom,


On 9/20/2016 9:13 AM, Tom Herbert wrote:
> ...
> For new encapsulation protocols please consider the effects of IP
> header alignment in the presence of Ethernet encapsulation. Defining
> Ethernet encapsulation with the two byte padding like in ETHERIP may
> help a lot to make implementation of Ethernet encapsulation feasible
> on CPU HW.

IMO, alignment needs to be handled within each encapsulation layer
independently. I don't think it's useful to expect new encapsulation
layers to have to make sure every layer of an encapsulated packet is
aligned - just the first one ought to be sufficient. The rest is the
responsibility of whomever added the other layers already in place.

So yes, it's useful to make sure the encapsulated packet starts on a
boundary that is 4-byte aligned, but the rest *needs to be* someone
else's problem.

Joe