On Tue, Nov 21, 2023, 11:44 AM Templin (US), Fred L <Fred.L.Templin= [email protected]> wrote:
> Section 8 of "Identification Extension for the Internet Protocol" proposes > a new IPv6 extension > header called the "Extended Fragment Header" that includes a 96-bit (12 > octet) Identification > field making the total length of the extension header 128-bits (16 octets): > > https://datatracker.ietf.org/doc/draft-templin-intarea-ipid-ext/ > > However, the only reason for the 96-bit Identification field was to make > the whole > extension header be an integral multiple of 8 octets - what would be > preferable would > be to have only a 64-bit Identification field and limit the Extended > Fragment Header as > a whole to 96-bits (12 octets) which is not a multiple of 8 octets. > > The IPv6 Fragment Header is unique among IPv6 extension headers in that it > does not > include a "Hdr Ext Len" field that tells the length of the header in > 8-octet units. This > means that implementations must be able to determine its length (8 octets) > solely > based on the IP protocol number "44". The proposed IPv6 Extended Fragment > Header > would likewise not include a "Hdr Ext Len" field and would use a new IP > protocol > number to be assigned by IANA, with the IP protocol number determining the > extension header length. > > RFC8200, Section 4 states: > > "Each extension header is an integer multiple of 8 octets long, in > order to retain 8-octet alignment for subsequent headers." > > But, can an exception be made for the proposed IPv6 Extended Fragment > Header > with a 64-bit Identification field, making the total extension header > length 12 octets > which is not a integer multiple of 8? > Hi Fred, The text you quoted says why we can't do that. If a frag header length is not a multiple of eight bytes then the alignment requirements for all subsequent extension headers and the payload are not met. This potentially breaks a receiving implementation that relies on alignment. Tom > Thank you - Fred > > _______________________________________________ > Int-area mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/int-area >
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