Re: [Int-area] 答复: 答复: 答复: 答复: Is the UDP destination port number resource running out?// re: I-D Action: draft-ietf-intarea-gue-04.txt

[Tom Herbert <[e-mail]>]

On Thu, May 25, 2017 at 12:44 PM, Templin, Fred L
<[e-mail]> wrote:
> If you are talking about the GUE direct encapsulation of IPv4 and IPv6, I
> agree
>
> with the current spec and that direct encapsulation (i.e., with no
> additional
>
> encapsulations between the IP/UDP and inner IP headers) is desirable and
>
> should remain as part of the spec. I think we may be over-thinking this.
>
+1. I think a little too much has been inferred beyond the what is
actually in draft. Versions are straightforward:

- There is a two bit version number field that begins GUE header. The
format of the rest of the header depends on the version.
- Version 0 defines an encapsulation header that encapsulates by IP
protocol number.
- Version 1 defined a means for direct encapsulation of select
protocols as an optimization. Formats for IPv4 and IPv6 are defined.
- Version 2 and 3 are reserved

Rather Version 1 constitutes a new version or a different format seems
to be a matter of terminology, however semantically and implementation
wise the intent is clear. If it's necessary the field could be renamed
"version/format"

Tom

>
>
> Fred
>
>
>
> From: Int-area [mailto:[e-mail]] On Behalf Of Joe Touch
> Sent: Thursday, May 25, 2017 12:08 PM
> To: Tom Herbert <[e-mail]>
> Cc: [e-mail]
> Subject: Re: [Int-area] 答复: 答复: 答复: 答复: Is the UDP destination port number
> resource running out?// re: I-D Action: draft-ietf-intarea-gue-04.txt
>
>
>
>
>
>
>
> On 5/25/2017 11:47 AM, Tom Herbert wrote:
>
> You can't put bare Ethernet inside GUE. You need to use EtherIP -
>
> exactly because it has a 16-bit field, of which only the first 4 bits
>
> are (already) defined.
>
>
>
> My point is that EtherIP burns 16 bits vs bare Ethernet, but those 16
>
> bits allow it to be mapped to one of the IP versions (you picked IPv5).
>
> The same trick works for UDP and TCP - just pick a different 16 bit
>
> pattern for each one.
>
>
>
> Inserting two bytes before the TCP header breaks four byte alignment
>
> of the header which is a bigger hit than the benefit of saving two
>
> bytes. A nice side effect of the two byte header in EtherIP is that it
>
> aligns the Ethernet payload (e.g. an IP header) to four bytes.
>
> Maintaining this four byte alignment is still important to some CPU
>
> architectures most notably Sparc, but can even be problematic to x86
>
> under certain circumstances.
>
>
>
> Tom
>
> Sure - I'm not sure the 4-byte penalty is worth avoiding any nearly any
> case, frankly -- even for IP.
>
> Joe