Subject: Re: bin/29126: tcpdump leads to packet loss
To: None <gnats-bugs@netbsd.org, kern-bug-people@netbsd.org,>
From: Christos Zoulas <christos@zoulas.com>
List: netbsd-bugs
Date: 01/27/2005 11:39:25
On Jan 27,  4:06pm, kim@tac.nyc.ny.us (Kimmo Suominen) wrote:
-- Subject: Re: bin/29126: tcpdump leads to packet loss

| The following reply was made to PR kern/29126; it has been noted by GNATS.
| 
| From: kim@tac.nyc.ny.us (Kimmo Suominen)
| To: gnats-bugs@netbsd.org
| Cc: 
| Subject: Re: bin/29126: tcpdump leads to packet loss
| Date: Thu, 27 Jan 2005 11:05:26 -0500 (EST)
| 
|  I see the loss of traffic also happening on tlp and gsip and using dumb
|  switches (i.e. no STP in use).
|  
|  It definitely was not happening with earlier versions of NetBSD.
|  
|  The only "old" version I have around anymore is 1.6B.  The NIC's I have
|  on that are fxp and tlp.  Neither one exhibits this problem.
|  
|  How to test:  start tcpdump on the interface you are connected over,
|  and hit RETURN repeatedly to verify if tty echoes it back immediately.
|  
|      inet-fw:~# tcpdump -i tlp0 port 22
|      tcpdump: listening on tlp0
|  

Some nics reset the interface when they enter or exit promiscuous mode,
dropping link. If you are connected over a switch
that does spanning tree it might take some time to recalc. During that
time, the network does not work at all over that interface.

christos