what if, for testing purposes i want only to redirect the traffic from certain ip, say 10.6.2.250
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routing traffic to a content filter using iptables
I have a fedora firewall for my organization, now I am also setting up a new linux-based box with a proxy/content filter. What I want, is to redirect all outgoing port 80 traffic to get out through the proxy using iptables. Both servers are on the same subnet (the firewall and the new proxy), and both are connected directly to Internet.
All my machines are configured to use the firewall as gateway to the internet.
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Answers
First of all, my rules have typo
iptables -t nat -A PREROUTING -i eth1 -p tcp --dport 80 -s 10.6.2.250 -j DNAT --to ip.of.the.proxy:80
#if ip.of.the.proxy is accessible via same eth device as ip.of.the.proxy, then one more rule is needed
#unfortunately this will cause proxy to see connection from firewall (instead of real client).
#if it's unacceptable, I propose to create third network, where are only firewall and the proxy
iptables -t NAT POSTROUTING -o eth1 -s 10.6.2.250 -d ip.of.the.proxy -j MASQUERADE
here what i want to achieve, it should be possible... i still want them to use the same gateway but another connection for internet.
- iptables.png
- 38 KB
iptables
That exactly what You need
ETH_INSIDE=eth1
iptables -t nat -A PREROUTING -i $ETH_INSIDE -p tcp --dport 80 -s 10.6.2.250 -j DNAT --to-destination 10.6.4.235:80
iptables -t nat -A POSTROUTING -o $ETH_INSIDE -s 10.6.0.0/16 -d 10.6.4.235 -j SNAT --to-source 10.6.4.234
but note, that proxy will not see the client's IP, firewall's instead.
Not in this config.
You see CLIENT connects to FW, FW forwards packets to PROXY. But if FW will not change source ip, then PROXY will reply directly to CLIENT. CLIENT will consider that IP spoofing(it sent packet to one ip, but reply come back from another one) and drop it.
Maybe You should do something like
client(10.6.2.250) --- firewall(10.6.4.234 & 192.168.8.234, NAT only to internet) --- internet
|
proxy (192.168.8.235 with static route to 10.0.0.0/8 via 192.168.8.234, no NAT, no ip_forward) --- internet
then it's enough to
ETH_INSIDE=eth1
iptables -t nat -A PREROUTING -i $ETH_INSIDE -p tcp --dport 80 -s 10.6.2.250 -j DNAT --to-destination 192.168.8.235:80
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by: shakoush2001Posted on 2008-04-15 at 13:39:46ID: 21362647
iptables -t nat -A PREROUTING -j DNAT -i eth1 -p tcp --dport 443 --to-destination 192.168.0.2:443
change the nic/port/ip accordingly