Subject: kern/7783: SM91C92 driver sees duplicated outbound packet on bpf
To: None <>
From: None <>
List: netbsd-bugs
Date: 06/15/1999 16:35:50
>Number:         7783
>Category:       kern
>Synopsis:       SM91C92 driver sees duplicated outbound packet on bpf
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people (Kernel Bug People)
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Jun 15 16:35:00 1999
>Originator:     jun-ichiro itojun hagino
KAME project
>Release:        NetBSD 1.4/i386
NetBSD 1.4 NetBSD 1.4 (LYCHEE.v6) #191: Tue Jun 15 12:02:47 JST 1999 i386

When using SMC91C92 ethernet interface (MegaHertz XJ10BT card,
recognized by "sm" driver) bpf captures outbound packet twice,
even though the packet appears only once on the wire.

This could cause problem when you use IPv6 duplicated address detection (RFC2462 5.4).
The protocol is like this:
	When assigning IPv6 address x to a node, the node will 
	transmit packet toward x to detect duplication of address.
	If no packet is received, there is no duplicate.
If you see outbound packet loops back to oneself, the protocol will always fail.
on a window,
# tcpdump -n -i sm1 host myhost
on other window,
# ping otherhost
you will see icmp echo request twice on tcpdump output.
Sorry I have no clue.  Maybe chip initialization issue?