>Number:         7196
>Category:       kern
>Synopsis:       multicast gets bad checksums
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people (Kernel Bug People)
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Mar 18 09:05:00 1999
>Last-Modified:
>Originator:     Wolfgang Rupprecht
>Organization:
W S Rupprecht Computer Consulting, Fremont CA
>Release:        NetBSD-current 3/18/99
>Environment:
	
System: NetBSD pasillo.wsrcc.com 1.3K NetBSD 1.3K (WSRCC505) #0: Sun Mar 14 20:21:08 PST 1999 root@capsicum.wsrcc.com:/v/src/netbsd/NetBSD-current/usr/src/sys/arch/i386/compile/WSRCC505 i386


>Description:
	multicast/udp and tcpdump disagree on the validity of the checksums.
        There are times when 100% of them show as bad, other times they mostly 
	show as good.

>How-To-Repeat:
	run any udp signal generator program with output to a multicast addr.
	run tcpdump and watch.  

    In the transcript below TX is de0 tulip driver (SMC 9332DST 21140
    pass 1.2), RX is ep0 3com 3c589 pcmcia.  Similar lossage observed
    between two de0 tulip hosts.

    # grep MCAST /etc/hosts
    224.0.1.235     DGPS.MCAST.NET
 
    # tcpdump -v host DGPS.MCAST.NET 
    tcpdump: listening on ep0
    08:44:49.910357 capsicum.wsrcc.com.65183 > DGPS.MCAST.NET.rtcm-sc104: [udp sum ok] udp 16 (ttl 16, id 1432)
    08:44:50.140315 capsicum.wsrcc.com.65179 > DGPS.MCAST.NET.2102: [udp sum ok] udp 8 (ttl 16, id 1435)
    08:44:50.910346 capsicum.wsrcc.com.65183 > DGPS.MCAST.NET.rtcm-sc104: [udp sum ok] udp 17 (ttl 16, id 1447)
    08:44:51.140436 capsicum.wsrcc.com.65179 > DGPS.MCAST.NET.2102: udp 88 (ttl 16, id 1448)
    08:44:51.910400 capsicum.wsrcc.com.65183 > DGPS.MCAST.NET.rtcm-sc104: [udp sum ok] udp 17 (ttl 16, id 1452)
    08:44:52.910373 capsicum.wsrcc.com.65183 > DGPS.MCAST.NET.rtcm-sc104: [bad udp cksum 40!] udp 27 (ttl 16, id 1456)
    08:44:53.140284 capsicum.wsrcc.com.65179 > DGPS.MCAST.NET.2102: [udp sum ok] udp 8 (ttl 16, id 1457)
    08:44:53.910409 capsicum.wsrcc.com.65183 > DGPS.MCAST.NET.rtcm-sc104: [udp sum ok] udp 17 (ttl 16, id 1462)
    08:44:54.140455 capsicum.wsrcc.com.65179 > DGPS.MCAST.NET.2102: udp 88 (ttl 16, id 1463)
    08:44:54.910372 capsicum.wsrcc.com.65183 > DGPS.MCAST.NET.rtcm-sc104: [udp sum ok] udp 17 (ttl 16, id 1464)
    08:44:55.910414 capsicum.wsrcc.com.65183 > DGPS.MCAST.NET.rtcm-sc104: [udp sum ok] udp 16 (ttl 16, id 1465)
    08:44:56.140989 capsicum.wsrcc.com.65179 > DGPS.MCAST.NET.2102: [udp sum ok] udp 8 (ttl 16, id 1466)
    08:44:56.910406 capsicum.wsrcc.com.65183 > DGPS.MCAST.NET.rtcm-sc104: [udp sum ok] udp 17 (ttl 16, id 1471)
    08:44:57.140500 capsicum.wsrcc.com.65179 > DGPS.MCAST.NET.2102: udp 88 (ttl 16, id 1472)
    08:44:57.910462 capsicum.wsrcc.com.65183 > DGPS.MCAST.NET.rtcm-sc104: [bad udp cksum 6948!] udp 28 (ttl 16, id 1473)
    08:44:58.910408 capsicum.wsrcc.com.65183 > DGPS.MCAST.NET.rtcm-sc104: [udp sum ok] udp 16 (ttl 16, id 1474)
    08:44:59.140188 capsicum.wsrcc.com.65179 > DGPS.MCAST.NET.2102: [udp sum ok] udp 8 (ttl 16, id 1475)
    ^C
    97 packets received by filter
    0 packets dropped by kernel


>Fix:
	unknown.
>Audit-Trail:
>Unformatted: