Below are some sought-after interview questions asked, related to Squid

Question1: What is Squid?

Answer: Squid is an Application software that works as a proxy server as well as web cache Daemon. Squid Protocols such as FTP, HTTP, HTTPS, SSL,TLS, are supported by the proxy server Squid. It performs caching of web and DNS for frequently visited websites. Platforms supports by the Squid are Linux, UNIX, Microsoft Windows and Mac.

Question2: What is the default port of squid and how to change its operating port?

Answer: 3128 is the default port squid lisitens on.

Question3: What do you mean by Proxy Server and use of Proxy Server in Computer Networks?

Answer: Proxy Server is a physical machine or an application that acts as a mediator between client and server. A client requests for data from the the proxy server and proxy server manages to respond accordingly.

Question4:How to block certain domains through squid proxy server?

Answer: We do the following configuration:

a. Create a file say checklist under directory /etc/squid.

"# touch /etc/squid/checklist"

b. Open the file /etc/squid/checklist in an editor say "nano".

"# nano /etc/squid/checklist"

c. Add all the domains to the file checklist with one domain per line.

.rediffmail.com .facebook.com .twitter.com.. .gmail.com...

d. Save the file and exit. Now open the Squid configuration file Path: /etc/squid/squid.conf.

"# nano /etc/squid/squid.conf"

e. Add the given lines below to the Squid configuration file.

acl CHECKLIST dstdom_regex -i /etc/squid/checklist http_access deny checklist

f. Save the configuration file and exit. Restart Squid service to make the changes effective.

"# service squid restart"

Question5: Media Range Limitation and partial download in Squid?

Answer: It is one of the feature of Squid that request only the required data from the server and not the whole file. This feature is used for videos streaming websites like Metacafe and Youtube that helps user to see the specific part of the video instead of running the whole video.

Question6: Reverse proxy in squid

Answer: It is one of the feature of Squid supports in accelerating the web surfing for end user.

For example: Let us say there is a Main server MS that contains the resource file and PS is the proxy Server. Now the client requests for the resource file which is available at MS. client will rely on MS for the the resource file for the first time and the copy of that file gets stored on PS for configurable amount of time. For every request for this resourse file from now onwards PS becomes the main source.

Advantages: Reduced traffic, Reduced CPU usages, Reduced resource utilization and hence reduced load to main server RS.

Question7: How will one clear the Squid Cache? As Squid can be used as web-cache Daemon.

Answer: Following are the steps to clear the Squid Cache.

a. Stop Squid proxy server and delete the cache from the location /var/lib/squid/cache directory.

"# service squid stop" "# rm -rf /var/lib/squid/cache/*<"

b. Create Swap directories.

"# squid -z"

1. To restrict the web access we can write the following lines and restrict the site access for a certain period for the week days?

a. To restrict web access between 3 to 18 from Tuesday to Thrusday, open the Squid configuration file.

"# nano /etc/squid/squid.conf"

b. Include the following lines in squid.conf file, now save and exit.

acl ALLOW_TIME time T W H 15:00-18:00 shttp_access allow ALLOW_TIME

c. Restart the Squid Service.

"# service squid restart"

Question9: Squid stores data in which file format?

Answer: Squid stores data in ufs (Unix File System) format also called the Berkeley Fast File System.

Question10: Where do cache gets stored by squid?

Answer: There is a folder path: /var/spool/squid where squid stores cache.