Linux in General > Linux Tutorials & How To's
Configuring Squid Proxy server & Transparent Proxy
Ricky:
Hello..
After lots loads of questions about squid I decide to write this tutorial..
Here We are going to do our job in two major steps.
(a) Configuring Squid Proxy
(b) Making squid work in Transparent way
So (a) is for those who want squid working and if you want squid in transparent way then go for (a) and (b) both.
But before making squid transparent make sure you have seen
NAT / Interent Sharing in Linux How to
Part (a)
Configuring Squid for Simple Proxy
I encourage people to install squid from source code. If you want to use squid in transparent way then install squid with following options
This is to configure Squid with support for transparent proxy
--- Code: --- # enabling the transparent proxy feature during compliation.
./configure --enable-linux-netfilter
# then make
make
# then make install
make install
--- End code ---
After installing squid successfully we have to configure squid to work for us.
So open /usr/local/squid/etc/squid.conf and uncomment the options which you requires or use the following squid.conf and modify it according to your use..
--- Code: ---
# Set the maximums size of the object which will be cached.
maximum_object_size 8192 KB
# Set maximum physical RAM to be used for storing objects.
# NOTE: typically squid uses much more RAM then specified so when we said 16 MB then actually it is using around 25 MB RAM.
cache_mem 16 MB
# use to set where to store cache. here it is /cache of size 2048 MB.
# Here 22 and 256 are used to define directory structure so you don't have to touch it.
cache_dir ufs /cache 2048 22 256
# Here we are disabling cache_store_log as it will only increase disk usage.
# You can enable it anytime by specifying path instead of "none" directive"
cache_store_log none
# Here we are specifying that when we say "all " then it means whole internet.
# Also specifying some required acls.
acl all src 0.0.0.0/0.0.0.0
acl manager proto cache_object
acl localhost src 127.0.0.1/255.255.255.255
# Here specifying acls for which ports are allowed, which network is allowed to use our proxy .
# Here "your_netwrok" is the name use for your network.
# Change 192.168.0.0/255.255.255.0 to address of your LAN
acl your_network src 192.168.0.0/255.255.255.0
acl SSL_ports port 443 563
acl Safe_ports port 80 21 443 563 70 210 1025-65535
acl Safe_ports port 280
acl Safe_ports port 488
acl Safe_ports port 591
acl Safe_ports port 777
acl CONNECT method CONNECT
# Here giving permission for localhost ie this machine to access proxy.
http_access allow manager localhost
http_access deny manager
# Denying access to ports which are not safe
http_access deny !Safe_ports
http_access deny CONNECT !SSL_ports
# Allowing access to LAN and denying others.
http_access allow your_network
http_access deny all
icp_access allow all
miss_access allow all
# Give the email of your adminstrator which can be contacted if anything goes wrong by the users.
cache_mgr you@yourdomain.com
# Set here the hostname of your proxy box. You can set anything if don't have any FQDN .
visible_hostname you.yourdomain.com
unique_hostname you.yourdomain.com
# Directive for squid proxy to work also in Transparent mode.
# If not using transparent proxy then you still keep them.
httpd_accel_host vertual
httpd_accel_port 80
httpd_accel_with_proxy on
httpd_accel_uses_host_header on
# Set the port which will be used by clients to access squid proxy
http_port 3128
--- End code ---
Now you have your squid.conf ready to go. But before running squid run following to initialized the cache directory
--- Code: --- /usr/local/squid/sbin/squid -z
--- End code ---
If it don't give any error then we should move to next step.
Now run squid by (Internet should be already connected)
--- Code: ---/usr/local/squid/sbin/squid
--- End code ---
Now see /usr/local/squid/var/logs/cache.log if you see some thing like this..
--- Code: ---
2004/01/08 22:48:30| Ready to serve requests.
2004/01/08 22:48:30| Completed Validation Procedure
2004/01/08 22:48:30| Validated 7002 Entries
2004/01/08 22:48:30| store_swap_size = 63960k
2004/01/08 22:48:31| storeLateRelease: released 0 objects
--- End code ---
If you see some thing like above then you have squid configured correctly and it is working.
Now you have squid ready to use.
Note:
To Use squid configure your clients brower to use proxy by setting the ip of proxy server as your computer's ip running squid and specifying the port as 3128 or other which have changed in squid.conf . Make sure you add same port for SSL proxy as for HTTP proxy .
Now try to surf the net from client and check /usr/local/squid/var/logs/access.log to see whether the site you have opened is recored in access.log to make sure your computer is using squid.
It is now all done. I have tried to make it simple and practical but there are various other aspect of squid which are not covered here. But I hope as you get your squid working then you will understand them all yourself.
Part (b)
Setting Up squid to run in Transparent Mode
After making sure that your proxy is working fine. You can use transparent proxy if you want to use it.
To run proxy in Transparent mode add the following lines to your NAT script as I specified here NAT / internet shaaring how to
--- Code: --- #Transparent proxy
iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -j REDIRECT --to-port 3128
--- End code ---
And now set your client's browser to not to use the proxy and open a site from client then check the access.log to see that the site opened by use is redirected to squid or not.
If you are able to open websites and also that is getting logged in access.log then your transparent proxy is up and working.
If this don't work but you are able to open sites using simple proxy then you are probably not having NAT. See NAT / internet sharing how to
lugoteehalt:
Sorry such a basic question but see a lot of stuff about 'transparent proxies':
What is a transparent proxy? Have looked in dictionaries but do not really understand.
Thanks for any help.
:D
ashwin_ice:
Thanks a Billion, Ricky... that was really considerate of you and I think that this would help a lot of people. And to those who need to understand what a transparent proxy is... BUT REMEMBER TO USE THE SETTINGS GIVEN IN RICKY'S TUTORIAL AS THE ONE GIVEN THERE IS MORE COMPLEX....
TRANSPARENT PROXY(For those Who Dont Know What a TransParent Proxy is):
A transparent cache is so named because it works by intercepting the network traffic transparently to the browser. In this mode, the cache short-circuits the retrieval process if the desired file is in the cache. Transparent caches are especially useful to ISPs because they require no browser setup modification. Transparent caches are also the simplest way to use a cache internally on a network, because they do not require explicit coordination with other caches. The purpose of this white paper is to discuss the various methods of implementating transparent caching using Squid on Linux with a policy based router, an externalL4 switch, and an L4 switch inside the Linux Squid box. First, some basic concepts will be discussed, followed by the advantages of transparent caching, and finally redirecting packets to Squid using IP-Chains.
What is transparent caching? The full explanation about the term "Transparent Caching and Transparent Proxying" depends on the context, but we can assume the context here is HTTP proxy/caches with transparent hijacking of port 80, which is the default HTTP traffic in the internet.
The difference is that the cache includes a cache, while the proxy only proxies without caching. The term transparent is overloaded, having different meanings depending on the situation. To some it means a setup that hijacks port 80 traffic where the client tried to go to other servers, to some it means a semantically transparent proxy that does not change the meaning or content of requests/replies. There is no such thing as a truly transparent proxy, only semitransparent and certainly not such a thing as a truly transparent cache. Squid can be configured to act transparently. In this mode, clients are not required to configure their browsers to access the cache, but Squid will transparently pick up the appropriate packets and cache requests. This solves the biggest problem with caching: i.e. getting users to use the cache server.
More Info : http://squid.visolve.com/white_papers/trans_caching.htm
But remember follow Ricky's suggestions or ure gonna screw up like I did :lol:
lugoteehalt:
Right, so a proxy is a second computer that also holds a web page, say. Proxy 'The management of another's affairs.'
And transparent means the browser 'sees through it' - if it does not have the desired page it just lets the browser's request out to the net.
Sorry if being dense :D
Ricky:
Hmm.. well Transparent proxy is Proxy+NAT
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