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We use Varnish as our front-end web cache and load balancer, so we have a Linux server in our development environment, running Varnish with some basic caching and load-balancing rules across a pair of Windows 2008 IIS web servers.

We have a wildcard DNS rule that points *.development at this Varnish box, so we can browse,, etc. The problem is that since Varnish can't handle HTTPS traffic, we can't access

For dev/testing, we don't need any acceleration or load-balancing - all I need is to tell this box to act as a dumb proxy and forward any incoming requests on port 443 to a specific IIS server. I suspect iptables may offer a solution but it's been a long while since I wrote an iptables rule. Some initial hacking has got me as far as

iptables -F
iptables -A INPUT -p tcp -m tcp --sport 443 -j ACCEPT
iptables -A OUTPUT -p tcp -m tcp --dport 443 -j ACCEPT
iptables -t nat -A PREROUTING -p tcp --dport 443 -j DNAT --to
iptables -t nat -A POSTROUTING -p tcp -d --dport 443 -j MASQUERADE
iptables -A INPUT -j LOG --log-level 4 --log-prefix 'PreRouting '
iptables -A OUTPUT -j LOG --log-level 4 --log-prefix 'PostRouting '
iptables-save > /etc/iptables.rules

(where is the IIS box hosting the HTTPS website), but this doesn't appear to be working.

To clarify - I realize there's security implications about HTTPS proxying/caching - all I'm looking for is completely transparent IP traffic forwarding. I don't need to decrypt, cache or inspect any of the packets; I just want anything on port 443 to flow through the Linux box to the IIS box behind it as though the Linux box wasn't even there.

Any help gratefully received...

EDIT: Included full iptables config script.

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Have you open the port 443 to traffic before apply this rule? – Bruno Vieira Oct 26 '12 at 14:39
@Bruno I believe so... how would I check? – Dylan Beattie Oct 26 '12 at 15:00
iptables -A INPUT -p tcp -m tcp --sport 443 -j ACCEPT iptables -A OUTPUT -p tcp -m tcp --dport 443 -j ACCEPT Yes you did – Bruno Vieira Oct 26 '12 at 15:28
Check if you have this line marked on your sysctl file: net.ipv4.ip_forward=1 – Bruno Vieira Oct 26 '12 at 15:34
Ah... yes, but I hadn't run /sbin/sysctl -p after editing sysctl.conf... it's now working beautifully. Thanks for your help. – Dylan Beattie Oct 26 '12 at 15:39

2 Answers 2

up vote 1 down vote accepted

Here's what you should do to redirect the traffic from one host to another one in a specific port, please note that EVERY request for port 443 will be redirect to the host you are pointing on iptables:

1) Open port 443 to traffic:

iptables -A INPUT -p tcp -m tcp --sport 443 -j ACCEPT
iptables -A OUTPUT -p tcp -m tcp --dport 443 -j ACCEPT

2) Add specific rules to redirect incoming and outcoming data

iptables -t nat -A PREROUTING -p tcp --dport 443 -j DNAT --to
iptables -t nat -A POSTROUTING -p tcp -d --dport 443 -j MASQUERADE

3) Alternatively you can redirect the traffic that is coming from a specific host like:

 iptables -t nat -A PREROUTING -s ip._not_.listening -p tcp --dport 443 -j DNAT --to-destination

(This step is specially useful in case you want to handle port 443 in other client under your network)

4) Inform the kernel that you will accept ip forwarding

edit file /etc/sysctl.conf (or the one that suits your distro) and append (or change)


and then issue the command

sysctl -p /etc/sysctl.conf (or the file that suits your distro)

I hope it helped

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One more detail - I needed to edit /etc/network/interfaces to make the iptables changes persistent, as documented in - it's now working perfectly. Thanks. – Dylan Beattie Oct 26 '12 at 17:33

Ok, here's the full solution - this is on 12.04 LTS (GNU/Linux 3.2.0-23-generic x86_64)

First, I had to enable ip4 port forwarding by editing /etc/sysctl.conf and uncommenting the line:


Then I had to run /sbin/sysctl -p to make this change take effect.

Next to configure (and capture) the iptables rules script:

# flush any existing rules 
iptables -F
# Configure iptables to allow incoming traffic on port 443
iptables -A INPUT -p tcp -m tcp --sport 443 -j ACCEPT
# Configure iptables to allow outgoing traffic on port 443
iptables -A OUTPUT -p tcp -m tcp --dport 443 -j ACCEPT
# Configure iptables to NAT incoming 443 traffic to
iptables -t nat -A PREROUTING -p tcp --dport 443 -j DNAT --to
# Configure iptables to route responses from these requests back to the original requester
iptables -t nat -A POSTROUTING -p tcp -d --dport 443 -j MASQUERADE
# Dump the ruleset and save it into the file /etc/iptables.rules
iptables-save > /etc/iptables.rules

Finally, to make the change persist across reboots, I had to edit /etc/network/interfaces:

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto eth0
iface eth0 inet static
    # dns-* options are implemented by the resolvconf package, if installed

    # The next line was added to enable iptables rules on system restart
    pre-up iptables-restore < /etc/iptables.rules
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