[e2e] UDP length field

[Joe Touch]

Bill Sommerfeld wrote:
> 
> >       Why does UDP have a length field?
> 
> Same reason tcp does: to preserve an end-to-end length in the presence
> of fragmentation.
> 
> The ip packet length is the length of a particular fragment, and may
> have been set by a router which fragmented the packet.
> 
> The udp length appears only in the first fragment and describes the
> fully assembled datagram.

The reassembled packet should have had the IP packet length restored
during reassembly.

Joe