Iptables or something to redirect IP in gateway (GNU/Linux)

Question

Im writing a bash scripting to account traffic in my network server:

WAN:eth1 -> GNU/Linux Server:eth0 -> Users The GNU/Linux server uses squid, bind, QoS, mysql, lighttpd.

After an IP exceed the established quota a new QoS rule is applied for that IP (user) too exist one "flag" to decide when is restored the IP counter to Zero.

Some IPs and subnets work without quotas, other gruop of ips/subnets work with new QoS after quota is exceeded, and now I wanna work with a third group with redirection after quota is exceeded.

When an IP exceed the established quota all http traffic must be redirected to host (lighttpd runing on GNU/Linux ) and DROP all other traffic generated for that IP. In webserver exist a webpage with: "You exceed your daily quote of traffic, please wait "x" hours or call to your provider to purchase an extra navigation package" or something like that.

Is possible using a chain, or how can I do that?. The most topics that I found in Internet, are related to block all and create a new chain to let out to Internet (not work for me). And other redirect only IP by IP, but how can I create something that a "chain" and attach the IPs to must me redirected to can after restore that IPs easly?

Thanks for help and sorry for my poor English :S.

Answer 1

Are you looking for something like this?

iptables -t nat -A PREROUTING -s 192.168.100.66 -p tcp --dport 80 -j REDIRECT --to-ports 80
iptables -I INPUT 1 -i lo -s 192.168.100.66 -j ACCEPT
iptables -I INPUT 2 -i eth1 -d 192.168.100.66 -j DROP

This will redirect packets from 192.168.100.66 on port 80 to the local webserver on the loopback interface, allow that conversation, then reject all other packets being routed to 192.168.100.66 on the WAN interface.

To restore the connection back to normal you will want to delete those firewall entries:

iptables -t nat -D PREROUTING -s 192.168.100.66 -p tcp --dport 80 -j REDIRECT --to-ports 80
iptables -D INPUT -i lo -s 192.168.100.66 -j ACCEPT
iptables -D INPUT -i eth1 -d 192.168.100.66 -j DROP

Answer 2

Note that iptables itself (well, the xtables-addons extension set providing quota2) can already do the quota matching magic and you can (re)set the values through procfs, combined with REDIRECT as @resmon6 says:

-t nat -s user1addr -m quota2 --name user1 ! --quota 0 -j REDIRECT...
-t nat -s user2addr -m quota2 --name user2 ! --quota 0 -j REDIRECT...

The syntax is a arguably a little odd right now (0 is the initial value only and is independent from the runtime quota test involving the negational !. Noticing this just now, a patch may make it in to unroll this confusing syntax in the future).