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iptables as "proxy" and a filter
Post 302927078 by Smiling Dragon on Sunday 30th of November 2014 07:02:17 PM
11-30-2014
One thing I note in your friend's script is that it sets the firewall to drop all incoming connections before allowing port 22 (ssh) connections. If something goes wrong along the way on this, you'll need console access to get back in :/ I'd recommend setting the -P INPUT DROP last tbh 
As you've noted, this is just INPUT filters, your one is just NAT/IPMASQ. So it's like comparing apples and oranges really.
Looking just at your rules, I don't see anything untoward there, it appears that you are causing the proxy to accept traffic arriving on port 80 and redirecting it to 5.196.130.245.
An external customer connecting to the address would not be able to detect the redirect and would see all their connections as going to and coming back from the address of your proxy.
The webserver would see all the connections as coming from the proxy server address, unless the customer is setting "X-Forwarded-For" headers in their requests (not all that uncommon to find) which would be passed along to the webserver and quite possibly included in it's logs.
If you have a little more background of what your end goal is, we might be able to offer more advice
I would recommend also adding a FORWARD rule to DROP anything not for that port arriving from the external interface, as you've turned on IP forwarding and at present your setup would happily forward anything anyone asks it to. It's note really serious but could exacerbate any existing security issue into a full exploit.
As you've noted, this is just INPUT filters, your one is just NAT/IPMASQ. So it's like comparing apples and oranges really.
Looking just at your rules, I don't see anything untoward there, it appears that you are causing the proxy to accept traffic arriving on port 80 and redirecting it to 5.196.130.245.
An external customer connecting to the address would not be able to detect the redirect and would see all their connections as going to and coming back from the address of your proxy.
The webserver would see all the connections as coming from the proxy server address, unless the customer is setting "X-Forwarded-For" headers in their requests (not all that uncommon to find) which would be passed along to the webserver and quite possibly included in it's logs.
If you have a little more background of what your end goal is, we might be able to offer more advice
I would recommend also adding a FORWARD rule to DROP anything not for that port arriving from the external interface, as you've turned on IP forwarding and at present your setup would happily forward anything anyone asks it to. It's note really serious but could exacerbate any existing security issue into a full exploit.
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LEARN ABOUT XFREE86
xfindproxy
XFINDPROXY(1) General Commands Manual XFINDPROXY(1) NAME
xfindproxy - locate proxy services SYNOPSIS
xfindproxy -manager managerAddr -name serviceName -server serverAddr [-auth] [-host hostAddr] [-options opts] DESCRIPTION
xfindproxy is a program used to locate available proxy services. It utilizes the Proxy Management Protocol to communicate with a proxy manager. The proxy manager keeps track of all available proxy services, starts new proxies when necessary, and makes sure that proxies are shared whenever possible. The -manager argument is required, and it specifies the network address of the proxy manager. The format of the address is a standard ICE network id (for example, "tcp/blah.x.org:6500"). The -name argument is required, and it specifies the name of the desired proxy service (for example, "LBX"). The name is case insensitive. The -server argument is also required, and it specifies the address of the target server. The format of the address is specific to the proxy service specified with the -name argument. For example, for a proxy service of "LBX", the address would be an X display address (e.g, "blah.x.org:0"). The -auth argument is optional. If specified, xfindproxy will read 2 lines from standard input. The first line is an authoriza- tion/authentication name. The second line is the authorization/authentication data in hex format (the same format used by xauth). xfind- proxy will pass this auth data to the proxy, and in most cases, will be used by the proxy to authorize/authenticate itself to the target server. The -host argument is optional. If xfindproxy starts a new proxy service, it will pass the host specified. The proxy may choose to restrict all connections to this host. In the event that xfindproxy locates an already existing proxy, the host will be passed, but the semantics of how the proxy uses this host are undefined. The -options argument is optional. If xfindproxy starts a new proxy service, it will pass any options specified. The semantics of the options are specific to each proxy server and are not defined here. In the event that xfindproxy locates an already existing proxy, the options will be passed, but the semantics of how the proxy uses these options are undefined. If xfindproxy is successful in obtaining a proxy address, it will print it to stdout. The format of the proxy address is specific to the proxy service being used. For example, for a proxy service of "LBX", the proxy address would be the X display address of the proxy (e.g, "blah.x.org:63"). If xfindproxy is unsuccessful in obtaining a proxy address, it will print an error to stderr. SEE ALSO
proxymngr (1), Proxy Management Protocol spec V1.0 AUTHOR
Ralph Mor, X Consortium XFree86 Version 4.7.0 XFINDPROXY(1)