tcpdump mailing list archives
Re: odd issue with Linux VLAN interface
From: Guy Harris <guy () alum mit edu>
Date: Tue, 27 Jan 2015 16:15:16 -0800
On Jan 27, 2015, at 4:09 PM, Denis Ovsienko <denis () ovsienko info> wrote:
some time ago I did troubleshooting on a Linux PC and that involved running tcpdump with the "not tcp" filter on a few network interfaces to put a number of background TCP connections out of scope (I was interested how other protocols' packets were making from one interface to the other). At some point I had realized that tcpdump was printing TCP packets _only_ and no other protocols (again, the filter was "not tcp"). Later I figured it out how to reproduce the problem but not the cause of it. The host has an Ethernet interface with only an IPv6 link-local address (eth0). On top of it there is a VLAN interface with VID 75 (eth0.75), IPv6 link-local address and IPv4 address 10.0.75.254/24. The difference is, when tcpdump runs with "-i eth0.75", it works as expected and displays ARP and, for instance, UDP from/to the network 10.0.75.0/24. When run with "-i eth0", it displays only TCP from/to network 10.0.75.0. This looks wrong in two ways as the tagged packets should not appear on the bearing interface in the first place and even if they appear there the filter should exclude them, but instead of this it excludes all the other packets.
I.e., "tcpdump -i eth0 not tcp" prints *only* TCP packets? Just out of curiosity, what does "tcpdump -i eth0 -d not tcp" print? _______________________________________________ tcpdump-workers mailing list tcpdump-workers () lists tcpdump org https://lists.sandelman.ca/mailman/listinfo/tcpdump-workers
Current thread:
- odd issue with Linux VLAN interface Denis Ovsienko (Jan 27)
- Re: odd issue with Linux VLAN interface Guy Harris (Jan 27)
- Re: odd issue with Linux VLAN interface Denis Ovsienko (Jan 27)
- Re: odd issue with Linux VLAN interface Guy Harris (Jan 27)
- Re: odd issue with Linux VLAN interface Denis Ovsienko (Jan 27)
- Re: odd issue with Linux VLAN interface Michael Richardson (Jan 28)
- Re: odd issue with Linux VLAN interface Denis Ovsienko (Jan 27)
- Re: odd issue with Linux VLAN interface Guy Harris (Jan 27)
- Re: odd issue with Linux VLAN interface Denis Ovsienko (Jan 28)
- Re: odd issue with Linux VLAN interface Michael Richardson (Jan 28)