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For a very large network, it would make sense to configure a proxy server for every subnetwork and connect them to a parent proxy, which in turn is connected to the proxy cache of the ISP. To find the most appropriate server from which to get the objects, one cache sends an ICP request to all sibling proxies.
If multiple HIT responses were found, the proxy server decides from which server to download, depending on factors such as which cache sent the fastest answer or which one is closer. If no satisfactory responses are received, the request is sent to the parent cache. The more objects maintained in the network, the greater the possibility of finding the desired one.
Not all objects available in the network are static. Objects like this are not cached because they change each time they are accessed. The question remains as to how long all the other objects stored in the cache should stay there. To determine this, all objects in the cache are assigned one of various possible states. Other headers specifying that objects must not be cached are used as well. Objects in the cache are normally replaced, due to a lack of free hard disk space, using algorithms such as LRU last recently used.
Basically this means that the proxy expunges the objects that have not been requested for the longest time. The most important thing is to determine the maximum network load the system must bear.
Therefore, it is important to pay more attention to the load peaks, because these might be more than four times the day's average. When in doubt, it would be better to overestimate the system's requirements, because having Squid working close to the limit of its capabilities could lead to a severe loss in the quality of the service. The following sections point to the system factors in order of significance.
Speed plays an important role in the caching process, so this factor deserves special attention. For hard disks, this parameter is described as random seek time , measured in milliseconds.
Because the data blocks that Squid reads from or writes to the hard disk tend to be rather small, the seek time of the hard disk is more important than its data throughput. For the purposes of a proxy, hard disks with high rotation speeds are probably the better choice, because they allow the read-write head to be positioned in the required spot more quickly. One possibility to speed up the system is to use a number of disks concurrently or to employ striping RAID arrays.
In a small cache, the probability of a HIT finding the requested object already located there is small, because the cache is easily filled and the less requested objects are replaced by newer ones. If, for example, one GB is available for the cache and the users only surf ten MB per day, it would take more than one hundred days to fill the cache. The easiest way to determine the needed cache size is to consider the maximum transfer rate of the connection.
If all this traffic ends up in the cache, in one hour it would add up to MB and, assuming that all this traffic is generated in only eight working hours, it would reach 3. Because the connection is normally not used to its upper volume limit, it can be assumed that the total data volume handled by the cache is approximately 2 GB.
This is why 2 GB of disk space is required in the example for Squid to keep one day's worth of browsed data cached. The amount of memory RAM required by Squid directly correlates to the number of objects in the cache. Squid also stores cache object references and frequently requested objects in the main memory to speed up retrieval of this data.
Random access memory is much faster than a hard disk. In addition to that, there is other data that Squid needs to keep in memory, such as a table with all the IP addresses handled, an exact domain name cache, the most frequently requested objects, access control lists, buffers, and more. It is very important to have sufficient memory for the Squid process, because system performance is dramatically reduced if it must be swapped to disk.
The cachemgr. This tool is introduced in Section Squid is not a program that requires intensive CPU usage. The load of the processor is only increased while the contents of the cache are loaded or checked. Using a multiprocessor machine does not increase the performance of the system.
To increase efficiency, it is better to buy faster disks or add more memory. If not already installed, install the squid package. To ensure a smooth start-up, the network should be configured in a way that at least one name server and the Internet can be reached.
Problems can arise if a dial-up connection is used with a dynamic DNS configuration. To start Squid, enter rcsquid start at the command line as root. If done appears to the right in green, Squid has been successfully loaded. To test the functionality of Squid on the local system, enter localhost as the proxy and as the port in the browser.
However, in doing so, consider that Squid is made completely accessible to anyone by this action. Therefore, define ACLs that control access to the proxy. More information about this is available in Section Do this with rcsquid reload.
Alternatively, completely restart Squid with rcsquid restart. The command rcsquid status can be used to check if the proxy is running. The command rcsquid stop causes Squid to shut down. Terminating Squid with kill or killall can damage the cache. To be able to restart Squid, a damaged cache must be deleted. If Squid should be loaded automatically when the system boots, use the YaST runlevel editor to activate Squid for the desired runlevels.
See Section An uninstall of Squid does not remove the cache hierarchy or the log files. Setting up a local DNS server makes sense even if it does not manage its own domain. It then simply acts as a caching-only name server and is also able to resolve DNS requests via the root name servers without requiring any special configuration see Section How this can be done depends on whether or not you chose dynamic DNS during the configuration of the Internet connection.
This way Squid can always find the local name server when it starts. With static DNS, no automatic DNS adjustments take place while establishing a connection, so there is no need to change any sysconfig variables. To start Squid for the first time, no changes are necessary in this file, but external clients are initially denied access.
The proxy is available for localhost. The default port is Nearly all entries begin with the lines are commented and the relevant specifications can be found at the end of the line. The given values almost always correlate with the default values, so removing the comment signs without changing any of the parameters actually has little effect in most cases.
If possible, leave the sample as it is and insert the options along with the modified parameters in the line below. This way, the default values may easily be recovered and compared with the changes. If you try to use the old squid. This is the port on which Squid listens for client requests. The default port is , but is also common.
If desired, specify several port numbers separated by blank spaces. Here, enter a parent proxy, for example, if you want to use the proxy of your ISP. As hostname , enter the name or IP address of the proxy to use and, as type , enter parent. For proxy-port , enter the port number that is also given by the operator of the parent for use in the browser usually Set the icp-port to 7 or 0 if the ICP port of the parent is not known and its use is irrelevant to the provider.
In addition, default and no-query may be specified after the port numbers to prohibit the use of the ICP protocol. Squid then behaves like a normal browser as far as the provider's proxy is concerned. This entry defines the amount of memory Squid can use for very popular replies. The default is 8 MB. This does not specify the memory usage of Squid and may be exceeded. The numbers at the end indicate the maximum disk space in MB to use and the number of directories in the first and second level.
The ufs parameter should be left alone. When specifying the disk space to use, leave sufficient reserve disk space. The last two numbers for the directories should only be increased with caution, because too many directories can also lead to performance problems.
These three entries specify the paths where Squid logs all its actions. Normally, nothing is changed here. If Squid is experiencing a heavy usage burden, it might make sense to distribute the cache and the log files over several disks. If the entry is set to on , obtain readable log files. Some evaluation programs cannot interpret this, however. With this entry, mask IP addresses of clients in the log files.
The last digit of the IP address is set to zero if you enter You may protect the privacy of your clients this way. With this, set the password Squid should use for the anonymous FTP login.
It can make sense to specify a valid e-mail address here, because some FTP servers check these for validity. An e-mail address to which Squid sends a message if it unexpectedly crashes. The default is webmaster. If you run squid -k rotate , Squid can rotate secured log files. The files are numbered in this process and, after reaching the specified value, the oldest file is overwritten. Usually, your own domain is entered here, so entering www in the browser accesses your own Web server.
Otherwise it adds a line to the header like. Normally, you do not need to change these values. If you have a dial-up connection, however, the Internet may, at times, not be accessible. Squid makes a note of the failed requests then refuses to issue new ones, although the Internet connection has been reestablished. In a case such as this, change the minutes to seconds. Then, after clicking Reload in the browser, the dial-up process should be reengaged after a few seconds. To prevent Squid from taking requests directly from the Internet, use the above command to force connection to another proxy.
This might be necessary, for example, if you are using a provider that strictly stipulates the use of its proxies or denies its firewall direct Internet access. Squid provides a detailed system for controlling the access to the proxy.
By implementing ACLs, it can be configured easily and comprehensively. This involves lists with rules that are processed sequentially. ACLs must be defined before they can be used.
Some default ACLs, such as all and localhost , already exist. However, the mere definition of an ACL does not mean that it is actually applied. An ACL requires at least three specifications to define it.
The following are some simple examples:. For this, ACLs must be given.
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