Re: [lisp] Suggested UDP checksum text

[Margaret Wasserman <mrw at sandstorm.net>]

On Aug 31, 2009, at 5:47 PM, Dino Farinacci wrote:
>   UDP Checksum:  this field MAY be transmitted as zero by an ITR and
>      when received by an ETR, MUST accept the packet for forwarding.

Aside from the grammatical issue with this sentence (no subject), the  
ETR does not really "accept a packet for forwarding", it decapsulates  
it and forwards the inner packet.  So, this isn't quite right, either...

>      When an ITR transmits a non-zero value, an ETR MAY verify the
>      checksum value.

The ETR validates a checksum when it receives it, not when the ITR  
transmits it...


>  If the checksum is verified, the packet is
>      accepted for forwarding, otherwise, it is silently dropped.   
> Note,
>      even when the UDP checksum is transmitted as zero an intervening
>      NAT device can recalculate the checksum and rewrite the UDP
>      checksum field to non-zero.  See draft [UDP-TUNNELS] for details.

Is it really necessary for us to describe the normal parts of UDP  
checksum handling here?  What about saying less?  Something like:

UDP Checksum:  This is the UDP checksum field, as described in [RFC  
768] as updated by [UDP-TUNNELS].

And leave it at that?

Margaret