Re: [Rtg-dt-encap-considerations] [nvo3] Alignment and Ethernet encapsulation
Tom Herbert <tom@herbertland.com> Tue, 20 September 2016 17:48 UTC
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From: Tom Herbert <tom@herbertland.com>
Date: Tue, 20 Sep 2016 10:47:54 -0700
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To: Joe Touch <touch@isi.edu>
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Cc: Sowmini Varadhan <sowmini.varadhan@oracle.com>, "nvo3@ietf.org" <nvo3@ietf.org>, "rtg-dt-encap-considerations@ietf.org" <rtg-dt-encap-considerations@ietf.org>
Subject: Re: [Rtg-dt-encap-considerations] [nvo3] Alignment and Ethernet encapsulation
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On Tue, Sep 20, 2016 at 10:35 AM, Joe Touch <touch@isi.edu> wrote: > > > On 9/20/2016 10:29 AM, Tom Herbert wrote: >> On Tue, Sep 20, 2016 at 10:07 AM, Joe Touch <touch@isi.edu> wrote: >>> 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. >>> >> It's the Ethernet payload that we need to be four byte aligned not the >> Ethernet header. Just aligning Ethernet header to four bytes is not >> useful; that means the Ethernet payload, e.g. an IP packet, won't have >> four byte alignment and hence the misery of trying to process the >> packet. For the cost of two bytes ETHERIP gets things right in this >> regard! > If you've been handed Ethernet to encapsulate, then that is the header > whose alignment you should be optimizing. > > As you point out, you can't align both IP and Ethernet to 4-byte > boundaries at the same time. You can if you insert a two byte pad before the encapsulated Ethernet header like ETHERIP (RFC3378 does). Tom
- [Rtg-dt-encap-considerations] Alignment and Ether… Tom Herbert
- Re: [Rtg-dt-encap-considerations] [nvo3] Alignmen… Joe Touch
- Re: [Rtg-dt-encap-considerations] [nvo3] Alignmen… Tom Herbert
- Re: [Rtg-dt-encap-considerations] [nvo3] Alignmen… Joe Touch
- Re: [Rtg-dt-encap-considerations] [nvo3] Alignmen… Tom Herbert
- Re: [Rtg-dt-encap-considerations] [nvo3] Alignmen… Joe Touch
- Re: [Rtg-dt-encap-considerations] [nvo3] Alignmen… Tom Herbert
- Re: [Rtg-dt-encap-considerations] [nvo3] Alignmen… Joe Touch