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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