[6lowpan] fragmentation and HC2

["Julien Abeille (jabeille)" <jabeille at cisco.com>]

Hi,

 

I have a question regarding the use of HC2 together with fragmentation in RFC4944:

When sending a large fully compressable UDP packet, must all fragments contain HC_UDP encoding, or only the first one?

 

i.e.,  if the IP packet has flow label and traffic class = 0, payload length inferred from L2, next header = UDP, source and destination addresses link local with interface identifier inferred from L2 addresses, UDP length inferred from IP length field , and  I need 2 fragments:

 

In all cases, fragment 1 should look like :

FRAG1 dispatch, datagram size and tag | HC1 dispatch | HC1 encoding = 0xFB | HC2encoding | IPv6 hop limit | compressed source and dest UDP ports | UDP checksum | beginning of UDP payload

 

Does fragment 2 look like:

FRAGN dispatch, datagram size, tag and offset | HC1 dispatch | HC1 encoding = 0xFB | HC2encoding | IPv6 hop limit | compressed source and dest UDP port | UDP checksum | rest of UDP payload

or

FRAGN dispatch, datagram size, tag and offset | HC1 dispatch | HC1 encoding =0x FA | IPv6 hop limit | rest of UDP payload

 

Thank you,

Julien

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