Help interpretting firewall logs

Installing and Using OpenWrt
1

Hi,
I've recently setup OpenWRT so I'm only slowly learning my way around.
My config is out-of-the-box (included below), except my WAN in on eth0 and LAN is on eth1

After a day or so of running I examined the system.log and could see lots of "rejected wan in" messages which make sense, but I also see occasional pairs of logs that look like this:

reject wan in: IN=eth0 OUT= MAC=... SRC=x.x.x.x DST=[WAN_ADDRESS] LEN=52 TOS=0x00 PREC=0x00 TTL=122 ID=7653 PROTO=TCP SPT=993 DPT=50661 WINDOW=269 RES=0x00 ACK FIN URGP=0
drop wan invalid ct state: IN= OUT=eth0 SRC=[WAN_ADDRESS] DST=x.x.x.x LEN=40 TOS=0x00 PREC=0x00 TTL=64 ID=0 DF PROTO=TCP SPT=50661 DPT=993 WINDOW=0 RES=0x00 RST URGP=0

where x.x.x.x is some random IP address from outside. The "reject wan" looks as expected, but could someone please explain the second apparently 'outgoing' log - but, I hope, not actually going anywhere because it is says dropped.

Thanks,

firewall.@defaults[0]=defaults
firewall.@defaults[0].syn_flood='1'
firewall.@defaults[0].input='REJECT'
firewall.@defaults[0].output='ACCEPT'
firewall.@defaults[0].forward='REJECT'
firewall.@zone[0]=zone
firewall.@zone[0].name='lan'
firewall.@zone[0].network='lan'
firewall.@zone[0].input='ACCEPT'
firewall.@zone[0].output='ACCEPT'
firewall.@zone[0].forward='ACCEPT'
firewall.@zone[1]=zone
firewall.@zone[1].name='wan'
firewall.@zone[1].network='wan' 'wan6'
firewall.@zone[1].input='REJECT'
firewall.@zone[1].output='ACCEPT'
firewall.@zone[1].forward='REJECT'
firewall.@zone[1].masq='1'
firewall.@zone[1].mtu_fix='1'
firewall.@zone[1].log='1'
firewall.@forwarding[0]=forwarding
firewall.@forwarding[0].src='lan'
firewall.@forwarding[0].dest='wan'
firewall.@rule[0]=rule
firewall.@rule[0].name='Allow-DHCP-Renew'
firewall.@rule[0].src='wan'
firewall.@rule[0].proto='udp'
firewall.@rule[0].dest_port='68'
firewall.@rule[0].target='ACCEPT'
firewall.@rule[0].family='ipv4'
firewall.@rule[1]=rule
firewall.@rule[1].name='Allow-Ping'
firewall.@rule[1].src='wan'
firewall.@rule[1].proto='icmp'
firewall.@rule[1].family='ipv4'
firewall.@rule[1].target='ACCEPT'
firewall.@rule[1].icmp_type='echo-request'
firewall.@rule[2]=rule
firewall.@rule[2].name='Allow-IGMP'
firewall.@rule[2].src='wan'
firewall.@rule[2].proto='igmp'
firewall.@rule[2].family='ipv4'
firewall.@rule[2].target='ACCEPT'
firewall.@rule[3]=rule
firewall.@rule[3].name='Allow-DHCPv6'
firewall.@rule[3].src='wan'
firewall.@rule[3].proto='udp'
firewall.@rule[3].dest_port='546'
firewall.@rule[3].family='ipv6'
firewall.@rule[3].target='ACCEPT'
firewall.@rule[4]=rule
firewall.@rule[4].name='Allow-MLD'
firewall.@rule[4].src='wan'
firewall.@rule[4].proto='icmp'
firewall.@rule[4].src_ip='fe80::/10'
firewall.@rule[4].icmp_type='130/0' '131/0' '132/0' '143/0'
firewall.@rule[4].family='ipv6'
firewall.@rule[4].target='ACCEPT'
firewall.@rule[5]=rule
firewall.@rule[5].name='Allow-ICMPv6-Input'
firewall.@rule[5].src='wan'
firewall.@rule[5].proto='icmp'
firewall.@rule[5].icmp_type='echo-request' 'echo-reply' 'destination-unreachable' 'packet-too-big' 'time-exceeded' 'bad-header' 'unknown-header-type' 'router-solicitation' 'neighbour-solicitation' 'router-advertisement' 'neighbour-advertisement'
firewall.@rule[5].limit='1000/sec'
firewall.@rule[5].family='ipv6'
firewall.@rule[5].target='ACCEPT'
firewall.@rule[6]=rule
firewall.@rule[6].name='Allow-ICMPv6-Forward'
firewall.@rule[6].src='wan'
firewall.@rule[6].dest='*'
firewall.@rule[6].proto='icmp'
firewall.@rule[6].icmp_type='echo-request' 'echo-reply' 'destination-unreachable' 'packet-too-big' 'time-exceeded' 'bad-header' 'unknown-header-type'
firewall.@rule[6].limit='1000/sec'
firewall.@rule[6].family='ipv6'
firewall.@rule[6].target='ACCEPT'
firewall.@rule[7]=rule
firewall.@rule[7].name='Allow-IPSec-ESP'
firewall.@rule[7].src='wan'
firewall.@rule[7].dest='lan'
firewall.@rule[7].proto='esp'
firewall.@rule[7].target='ACCEPT'
firewall.@rule[8]=rule
firewall.@rule[8].name='Allow-ISAKMP'
firewall.@rule[8].src='wan'
firewall.@rule[8].dest='lan'
firewall.@rule[8].dest_port='500'
firewall.@rule[8].proto='udp'
firewall.@rule[8].target='ACCEPT'
firewall.@rule[9]=rule
firewall.@rule[9].name='no DNS'
firewall.@rule[9].src='wan'
firewall.@rule[9].dest_port='53'
firewall.@rule[9].target='DROP'
firewall.@rule[9].enabled='0'
2

That is a TCP RST being sent, which is how a connection is actively rejected. A web browser will tell the user "The site refused to connect." A port scanner will report "The port is closed."

1 Like
3

Thanks for the response:
Why don't I see the same drop/wan after all the other reject/wan/in? Do I need to modify the standard config or is all OK with this? Thx,

4

Because all the other connections aren't active connections.

The issue is, your config is not default - you enabled logging on the WAN zone. You have to recall that timed-out TCP connections will also be rejected too. This is why you see a RST for this connection and not all blocked TCP connections.

Basically - this was your router closing an old or stale TCP connection, not a block of un-established attempts traffic from WAN. You could change the firewall rules to DROP - then no RST packets will be sent to remote machines.

5

Thanks for the clear explanation. I have changed my rules to DROP.

6

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