> On Wed, 27 Jan 1999 10:37:28 PST 
>  Bill Fenner <fenner@parc.xerox.com> wrote:
> 
>  > 4.2.2.5 Header Checksum: RFC 791 Section 3.1
>  >    
>  >    As stated in Section [5.2.2], a router MUST verify the IP checksum of
>  >    any packet that is received, and MUST discard messages containing
>  >    invalid checksums.  The router MUST NOT provide a means to disable
>  >    this checksum verification.
> 
> Well then, I guess that pretty much answers the question, eh? :-)
> 
Many router manufacturers don't cares about this; they just decrement
TTL and increment checksum and forwards the packet.

But doing an IP checksum calculation for the IP header is cheap; just to
add 10 shorts. If the IP header is more than 20 bytes then the packet
must go the "long way" anyway. (to handle IP options)

-- Ragge