Date: Wed, 2 Feb 2005 20:20:46 -0500 From: Jeff Aitken <jaitken@aitken.com> To: freebsd-hackers@freebsd.org Subject: duplicate packets on a vlan interface Message-ID: <20050203012046.GB57845@eagle.aitken.com>
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I'm seeing a very strange problem involving a freshly-installed
5.3-RELEASE system using vlans.
The machine has a single active ethernet interface (em0) with a pair
of vlan pseudo-interfaces created on it:
em0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
options=1b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING>
ether 00:09:6b:71:8c:38
media: Ethernet 100baseTX <full-duplex>
status: active
vlan0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
inet A1.B1.C1.50 netmask 0xffffffc0 broadcast A1.B1.C1.63
ether 00:09:6b:71:8c:38
media: Ethernet 100baseTX <full-duplex>
status: active
vlan: 20 parent interface: em0
vlan1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
inet A2.B2.C2.56 netmask 0xffffff00 broadcast A2.B2.C2.255
ether 00:09:6b:71:8c:38
media: Ethernet 100baseTX <full-duplex>
status: active
vlan: 842 parent interface: em0
>From a remote machine, if I send a single packet to the IP address
configured on vlan0 (A1.B1.C1.50), I get a single packet in response.
However, if I send a single packet the address configured on vlan1
(A2.B2.C2.56), I get a total of 62 replies (the original plus 61
duplicates). Running a tcpdump on the machine sending the ICMP
requests clearly shows that it's only sending a single request, yet
running tcpdump (tcpdump -p -i vlan1) on the receiving host shows
that it is receiving a total of 62 echo-requests.
This does not appear to be unique to ICMP. Sending TCP packets seems
to yield the same packet duplication on the destination box. Oddly,
a traceroute does NOT generate the same result, so perhaps UDP packets
do not trigger whatever is going on.
A google search did not yield anything useful. Any ideas?
--Jeff
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