Module Name:	syssrc
Committed By:	sommerfeld
Date:		Sun Oct 17 16:00:01 UTC 1999

Modified Files:
	syssrc/sys/netinet: ip_input.c

Log Message:
In ip_forward():

Avoid forwarding ip unicast packets which were contained inside
link-level multicast packets; having M_MCAST still set in the packet
header flags will mean that the packet will get multicast to a bogus
group instead of unicast to the next hop.

Malformed packets like this have occasionally been spotted "in the
wild" on a mediaone cable modem segment which also had multiple netbsd
machines running as router/NAT boxes.

Without this, any subnet with multiple netbsd routers receiving all
multicasts will generate a packet storm on receipt of such a
multicast.  Note that we already do the same check here for link-level
broadcasts; ip6_forward already does this as well.

Note that multicast forwarding does not go through ip_forward().

Adding some code to if_ethersubr to sanity check link-level
vs. ip-level multicast addresses might also be worthwhile.


To generate a diff of this commit:
cvs rdiff -r1.92 -r1.93 syssrc/sys/netinet/ip_input.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.