how to debug an iptable problem?

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Occasional Visitor
I'm an iptables savage - I know just enough to know how thoroughly I could ruin my network configuration, and could use some help. I've tried to wrap my head around iptables several times over the years, and each time stagger away with a headache.

I've run into a problem where my AC68U drops WAN every 10 minutes on the dot. Turns out, AT&T uses 10 minute DHCP leases, and the DHCP renew request at 5 minutes isn't getting handled correctly.

I'm using FreshJR's Adaptive QoS on Merlin 384.17 and I see the DHCP expiring every 10 minutes and WAN dropping and reconnecting in the syslog. When I disable Adaptive QoS, everything works fine, and I see the DHCP renew event in syslog every 5 minutes.

I'm assuming there is an iptable rule in the FreshJR QoS script that is causing the DHCP requests to be dropped / blocked but I don't know enough about iptables to figure out the problem.

Can someone wiser in the way of iptables than I guide me with what command I should use to show all the rules so I can compare with and without Adaptive QoS to check the diff for possible problems?

Any assistance much appreciated!


Part of the Furniture
iptables-save > withqos.txt
# go and disable QoS
iptables-save > withoutqos.txt
diff withqos.txt withoutqos.txt


Occasional Visitor
Thanks, @dave14305!

To close the loop on this thread, dave14305 found the solution to my AC68U dropping WAN every 10 minutes whenever I enabled Adaptive QoS. For some reason Adaptive QoS is dropping the DHCP packets, and since my DHCP lease is only 10 minutes, it was resetting constantly.

If you're having issues with adaptive QoS and DHCP, see this post.

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