All things related to multicast

["Charles R. Anderson" <>]

On Mon, May 19, 2003 at 12:59:28PM -0700, Tom Pusateri wrote:
pusateri> A NULL register would just have a dummy IP header that doesn't
pusateri> have the header length set so we wouldn't calculate the checksum
pusateri> when parsing these.

Ok, so in the case where a router sends a Null Register with an IP
length of 20, type UDP, and an invalid checksum, you are checking that
checksum and dropping the Null Register.  IMO, you shouldn't base the
decision on the ip->ip_hl and you should instead rely on the Null-bit in
the PIM header to determine the behavior.

If the PIM spec doesn't specify what you fill in for the other parts of
the IP header, I would understand that to imply that the normal rules
for populating an IP header would apply.

Either way, for interoperability, it would be best to accept packets
formatted either way, and perhaps just don't check the Encapsulated IP
header checksum at all if the Null-bit is set, regardless of ip->ip_hl.

-- 
Charles R. Anderson
Network Engineer
Computing and Communications Center
Worcester Polytechnic Institute