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

[Joe Touch <[e-mail]>]

FWIW, my general concern with this service is that lacks a version
identifier, and cannot be extended to support such an identifier for
bare IP packets as payloads, as encouraged by RFC7605 Section 7.5

At a minimum, one of the first fields after the "Version 0" format
identifier (a name which is confusing, for this reason) needs to be a
version field, so that future variants of this service will not need a
new port assignment.

Joe


On 5/25/2017 12:07 PM, Joe Touch wrote:
>
>
>
> 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