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tcpdump no output on stdout

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From: Marian Hettwer
Subject: tcpdump no output on stdout
Date: Thursday, July 8, 2010 - 7:50 am

Hi all,

I'm experiencing a rather strang behaviour with tcpdump on OpenBSD 4.7 
i386 running on a vmware esx vsphere 4.
My tcpdump gives no output at all on stdout, but if I use the very same 
command with "-w foobar" it actually does dump packages.

I know that esx server are probably not supported, however, does anybody 
know a work around this behavior? Or out of curiosity, where is this 
behaviour coming from?

See below:

[root@openlb38-1] <~> # tcpdump
tcpdump: listening on em0, link-type EN10MB
^C
198 packets received by filter
0 packets dropped by kernel

aah, 198 packets I couldn't see... hm hm...

[root@openlb38-1] <~> # tcpdump -w foobar
tcpdump: listening on em0, link-type EN10MB
^C
211 packets received by filter
0 packets dropped by kernel
[root@openlb38-1] <~> # ls -l foobar
-rw-r--r--  1 root  wheel  16278 Jul  8 18:42 foobar
[root@openlb38-1] <~> #

When I load that file in wireshark, I can certainly see the expected 
packets.

Does that make sense?!

Some details to the system:

dmesg:
http://crivens.kernel32.de/~rabauke/OpenBSD/dmesg-esx-openbsd47.txt

[root@openlb38-1] <~> # uname -a
OpenBSD openlb38-1.mobile.rz 4.7 GENERIC#558 i386

[root@openlb38-1] <~> # ifconfig
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 33200
         priority: 0
         groups: lo
         inet 127.0.0.1 netmask 0xff000000
         inet6 ::1 prefixlen 128
         inet6 fe80::1%lo0 prefixlen 64 scopeid 0x3
em0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
         lladdr 00:50:56:26:fc:2b
         priority: 0
         media: Ethernet autoselect (1000baseT full-duplex,master)
         status: active
         inet6 fe80::250:56ff:fe26:fc2b%em0 prefixlen 64 scopeid 0x1
enc0: flags=0<> mtu 1536
         priority: 0
vlan132: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
         lladdr 00:50:56:26:fc:2b
         priority: 0
         vlan: 132 priority: 0 parent interface: em0
         groups: vlan
         inet6 fe80::250:56ff:fe26:fc2b%vlan132 prefixlen 64 scopeid 0x4
         inet 10.38.132.100 netmask 0xfffffc00 broadcast 10.38.135.255
vlan252: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
         lladdr 00:50:56:26:fc:2b
         priority: 0
         vlan: 252 priority: 0 parent interface: em0
         groups: vlan egress
         inet6 fe80::250:56ff:fe26:fc2b%vlan252 prefixlen 64 scopeid 0x5
         inet 10.38.252.100 netmask 0xffffff00 broadcast 10.38.252.255
pflog0: flags=141<UP,RUNNING,PROMISC> mtu 33200
         priority: 0
         groups: pflog

Cheers,
Marian
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Messages in current thread:
tcpdump no output on stdout, Marian Hettwer, (Thu Jul 8, 7:50 am)
Re: tcpdump no output on stdout, Damien Miller, (Thu Jul 8, 11:16 pm)
Re: tcpdump no output on stdout, Marian Hettwer, (Fri Jul 9, 1:10 am)