Date: Tue, 22 Oct 2002 23:55:09 -0400 From: "Eric W. Bates" <ericx@vineyard.net> To: <freebsd-net@freebsd.org> Subject: debugging VLANs with tcpdump Message-ID: <009701c27a47$fb2d6c80$3ee380cc@alice>
next in thread | raw e-mail | index | archive | help
While using tcpdump to debug a new VLAN config, I noticed some problems and wanted to ask whether I was simply doing something wrong. I have 3 vlan interfaces attached to an fxp. The 3 vlan are bridged, but the fxp is not included in the group. The fxp has no IP. vlan0 has the IP for the bridge group. fxp0: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1500 ether 00:02:b3:5b:dd:98 media: Ethernet autoselect (100baseTX <full-duplex>) status: active vlan0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500 inet 192.168.10.1 netmask 0xffffff00 broadcast 192.168.10.255 ether 00:02:b3:5b:dd:98 vlan: 5 parent interface: fxp0 lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384 inet 127.0.0.1 netmask 0xff000000 vlan1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500 ether 00:02:b3:5b:dd:98 vlan: 10 parent interface: fxp0 vlan2: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500 ether 00:02:b3:5b:dd:98 vlan: 20 parent interface: fxp0 I get the most useful information when I run tcpdump on the fxp. Doing so shows all the packets passing by the NIC and it labels VLAN packets with their tag. tcpdump -i fxp0 20:00:54.747032 802.1Q vlan#10 P0 192.168.10.98 > 192.168.10.1: icmp: echo request (ttl 32, id 232, len 60) 20:00:54.747210 802.1Q vlan#10 P0 192.168.10.1 > 192.168.10.98: icmp: echo reply (ttl 64, id 22505, len 60) As soon as I add an expression to the tcpdump, I lose the VLAN labels from the output. I tried: tcpdump -i fxp0 icmp tcpdump -i fxp0 vlan tcpdump -i fxp0 host fw.mvhost.com I also tried increasing verbosity (-vvv). Attaching tcpdump to a vlan was interesting. Presumably I was seeing only packets tagged with the pseudo-interface's VLAN ID; but the labels were gone again. Is this a bug? If not, how do I display the explicit tag information under more circumstances? Thanks for your time. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?009701c27a47$fb2d6c80$3ee380cc>