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.
Fred From: Int-area [mailto:int-area-boun...@ietf.org] On Behalf Of Joe Touch Sent: Thursday, May 25, 2017 12:08 PM To: Tom Herbert <t...@herbertland.com> Cc: int-area@ietf.org 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
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