I have a virtual interface
eth1:3 with IP address
188.8.131.52, I have set up an iptables rule to log packets coming on that interface using the interface's IP (I know iptables doesn't care about virtual interfaces labels), like this:
iptables -A INPUT -d 184.108.40.206 -j LOG --log-level warning --log-prefix "VIP3-IN: "
When I run tcpdump and send packets on this IP from another machine, I see them, so I assume they are received and handled properly by the kernel, but iptables never logs these packets, and when I run
iptables -nvL, the packets count for that rule isn't incremented, like if they never hit the rule (or like if iptables doesn't even see packets coming on that interface).
I first thought of another rule matching the packet, and thus handling it before it hits the LOG rule, so I removed every iptables rule and added only the logging rule, with no more success.
Server is running on RHEL 6.2, with a 2.6.32 kernel, virtualized on VMware ESX.
Here is the full output of
Chain INPUT (policy ACCEPT 40 packets, 2891 bytes) pkts bytes target prot opt in out source destination 0 0 LOG all -- * * 0.0.0.0/0 220.127.116.11 LOG flags 0 level 4 prefix `VIP3-IN: ' Chain FORWARD (policy ACCEPT 0 packets, 0 bytes) pkts bytes target prot opt in out source destination Chain OUTPUT (policy ACCEPT 34 packets, 3816 bytes) pkts bytes target prot opt in out source destination
And here is a sample of the tcpdump's output showing the incoming packets (
tcpdump -n -nn -vvv -i eth1 "host 18.104.22.168"):
10:26:01.259409 IP (tos 0x50, ttl 121, id 26746, offset 0, flags [DF], proto TCP (6), length 52) 22.214.171.124.62332 > 126.96.36.199.8888: Flags [S], cksum 0x8da8 (correct), seq 3373891789, win 8192, options [mss 1460,nop,wscale 8,nop,nop,sackOK], length 0
And finally, the
ifconfig eth1:3 output:
eth1:3 Link encap:Ethernet HWaddr 00:50:56:AC:35:35 inet addr:188.8.131.52 Bcast:184.108.40.206 Mask:255.255.252.0 UP BROADCAST RUNNING PROMISC MULTICAST MTU:1500 Metric:1
Helped by the above diagram, I've setup iptables rules in different tables to see where the packets are going. I've come up with the following script:
IPT_FILTER="iptables -t filter" IPT_MANGLE="iptables -t mangle" IPT_NAT="iptables -t nat" $IPT_FILTER -F $IPT_FILTER -X $IPT_FILTER -A INPUT -d 220.127.116.11/22 -j LOG --log-prefix "DEBUG filter: " $IPT_FILTER -Z $IPT_MANGLE -F $IPT_MANGLE -X $IPT_MANGLE -A PREROUTING -d 18.104.22.168/22 -j LOG --log-prefix "DEBUG mangle/prerouting: " $IPT_MANGLE -A INPUT -d 22.214.171.124/22 -j LOG --log-prefix "DEBUG mangle/input: " $IPT_MANGLE -Z $IPT_NAT -F $IPT_NAT -X $IPT_NAT -A PREROUTING -d 126.96.36.199/22 -j LOG --log-prefix "DEBUG nat/prerouting: " $IPT_NAT -Z
And it appears that packets go through the
nat/PREROUTING tables, but don't hit the
mangle/INPUT table, so I guess it takes the "No" branch on the "Data for the firewall". And being by no means a network or system expert (at most a power-user), this is where I get lost and don't understand what's going on...
FINAL EDIT (solution)
As suggested by @nodens in its answer, the problem was caused by RPF being in "Strict" mode... So much headaches for such a simple setting...