[e2e] UDP length field

[Hari Balakrishnan]

One of my visiting students, Lars-Ake Larzon (who is involved with the UDP-lite 
proposal), asked me a question that stumped me:

	Why does UDP have a length field?

His reasoning, which is reasonable, is that this information adds no value and 
only serves to cause confusion when the IP and UDP length fields mismatch.

	Does anyone have data on how often the two length fields mismatch in real life?

Finally, the RFCs seem silent on the following question:

	What should an end-receiver do when the lengths mismatch?  Is this up to the 
implementation?

I'm sure someone on this list knows the answers.  And I apologize if this has 
been discussed on the list before; I did a very cursory search on the archive 
and couldn't find anything relevant.

Thanks,
Hari