Date: Wed, 10 Apr 2013 16:32:33 +0200 From: Michal Dubiel <md@semihalf.com> To: freebsd-net@freebsd.org Subject: Corrupted octets seen by tcpdump Message-ID: <51657801.1080700@semihalf.com>
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Hi,
I would like to ask you for some hints about where to look next and how
could I debug the following issue:
I have a FreeBSD host with two Ethernet interfaces and a Linux host with
one interface, which connected each other as in the picture below:
eth0.100 --- eth0 --------------- mge0 --- vlan0
\
\
bridge0
/
/
mge1 --- vlan1
On FreeBSD host:
# ifconfig
mge0: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> metric
0 mtu 1500
options=8000b<RXCSUM,TXCSUM,VLAN_MTU,LINKSTATE>
ether 00:02:00:58:31:30
media: Ethernet autoselect (1000baseT <full-duplex>)
status: active
mge1: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> metric
0 mtu 1500
options=8000b<RXCSUM,TXCSUM,VLAN_MTU,LINKSTATE>
ether 00:02:01:58:31:30
media: Ethernet autoselect (1000baseT <full-duplex,master>)
status: active
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> metric 0 mtu 16384
options=3<RXCSUM,TXCSUM>
inet6 fe80::1%lo0 prefixlen 64 scopeid 0x5
inet6 ::1 prefixlen 128
inet 127.0.0.1 netmask 0xff000000
nd6 options=3<PERFORMNUD,ACCEPT_RTADV>
bridge0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu
1500
ether 02:89:b3:33:d2:00
inet 192.168.126.6 netmask 0xffffff80 broadcast 192.168.126.127
id 00:00:00:00:00:00 priority 32768 hellotime 2 fwddelay 15
maxage 20 holdcnt 6 proto rstp maxaddr 100 timeout 1200
root id 00:00:00:00:00:00 priority 32768 ifcost 0 port 0
member: mge1 flags=143<LEARNING,DISCOVER,AUTOEDGE,AUTOPTP>
ifmaxaddr 0 port 3 priority 128 path cost 20000
member: mge0 flags=143<LEARNING,DISCOVER,AUTOEDGE,AUTOPTP>
ifmaxaddr 0 port 2 priority 128 path cost 20000
vlan0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
ether 00:11:22:33:44:55
inet 172.18.0.254 netmask 0xffff0000 broadcast 172.18.255.255
media: Ethernet autoselect (1000baseT <full-duplex>)
status: active
vlan: 100 parent interface: mge0
vlan1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
ether 00:02:01:58:31:30
media: Ethernet autoselect (1000baseT <full-duplex,master>)
status: active
vlan: 100 parent interface: mge1
The test is to ping from the remote Linux host the vlan0 interface
(172.18.0.254). I intentionally changed the vlan0 MAC address to be
different than it's parent: the mge0 device. I know it is not good
configuration, but this allows me to reproduce the issue I'm asking
here. The problem is that if I start sniffing packets (using tcpdump) on
mge0 I observe correct ping requests, but on bridge0 interface I'm
getting corruptions:
# tcpdump -eni bridge0
15:34:15.624125 00:01:6c:ea:a1:70 > 00:11:22:33:44:55, ethertype 802.1Q
(0x8100), length 104: vlan 100, p 0, ethertype IPv4, IP13 bad-hlen 8
I'm always seeing the same corruption (0xdb octed in the place where the
first octet of IP header should be, plus one additional random octed
right after it). This corrupts the IP version and header length fields.
The interesting think is also that after those two bogus octets, the
rest of the packet in the correct form appears. However, I instrumented
the code of bridge interface (sys/net/if_bridge.c) and when I do
printf() directly from the mbuf of the beginning bytes of the received
packet I don't see any corruption there. I suspect there may be some
problem with tcpdump or its integration with the stack. Have anyone had
a similar problems/observations and does anybody have any hints on what
can be causing this corruption and how to debug it further?
I'm using FreeBSD 8.3 on ARM architecture. Thanks in advance for your
response.
Best regards,
Michal
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