I have a server that is receiving traffic from a mirror port on a switch. The interface that is connected to this mirror port is in promisc mode. When I use just a plain catch all tcpdump on the interface, like
tcpdump -nn -i eth1
I see a ton of traffic. I can even grep this for certain things like, say, port 443.
tcpdump -nn -i eth1 | grep 443
obviously this shows anything that has a 443 in it, not just port 443. I have visually inspected it and I do see stuff like this:
15:08:08.112550 IP 126.96.36.199.1430 > 188.8.131.52.443: . ack 35124 win 32768
But I want just port 443 so...
tcpdump -nn -i eth1 port 443 ... 0 packets captured
Weird. I am not seeing any traffic when I use a filter. I have tried "ip port", "dst port", and a few other filters. I have also tried filtering by the IP instead of port. Nothing.
eth1 Link encap:Ethernet HWaddr 00:24:81:A5:AD:7A inet6 addr: fe80::224:81ff:fea5:ad7a/64 Scope:Link UP BROADCAST RUNNING PROMISC MULTICAST MTU:1500 Metric:1 RX packets:4114781478 errors:0 dropped:1 overruns:0 frame:0 TX packets:17 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:2240970313430 (2.0 TiB) TX bytes:15155497 (14.4 MiB) Interrupt:98 Memory:fa000000-fa012800
This interface has seen a ton of traffic. And my filter is valid, right? Why do I not see anything?