LINUX ADMINISTRATION 1 www.educlash.com

UNIT 3 CHAPTER-2 2 www.educlash.com

CHAPTER 2 : ADDITIONAL NETWORK SERVICES Configuring a Time Server Network Time Protocol (NTP) is a protocol used to help synchronize your Linux system's clock with an accurate time source. that allow the general public to synchronize with proper time They are divided into two types Stratum 1: NTP sites using an atomic clock for timing. Stratum 2: NTP sites with slightly less accurate time sources. It is good practice to have at least one server on your network be the local time server for all your other devices. 3 www.educlash.com

HOW TO CONFIGURE NTP SERVICE Download and Install The NTP Package Download ntp-4.1.2-5.i386.rpm and install rpm The /etc/ntp.conf File The /etc/ntp.conf file is the main configuration file for Linux NTP In which you place the IP addresses of the stratum 1 and stratum 2 servers you want to use. www.educlash.com

USING A PAIR OF SAMPLE INTERNET-BASED NTP SERVERS: STEPS TO CREATE A CONFIGURATION FILE USING A PAIR OF SAMPLE INTERNET-BASED NTP SERVERS: 1) First we specify the servers you're interested in: server otherntp.server.org # A stratum 1 server at server.org server ntp.research.gov # A stratum 2 server at research.gov 2) Restrict the type of access you allow these servers. In this servers are not allowed to modify the run-time configuration or query your Linux NTP server. restrict otherntp.server.org mask 255.255.255.255 nomodify notrap noquery restrict ntp.research.gov mask 255.255.255.255 nomodify notrap noquery Note: mask 255.255.255.255 statement is really a subnet mask limiting access to the single IP address www.educlash.com

4) how to give full access without any restricting 3) If this server is also going to provide time for other computers or network.  restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap Note: You do so with a modified restrict statement removing the noquery keyword to allow the network to query your NTP server 4) how to give full access without any restricting  restrict 127.0.0.1 It will give full access to localhost 5) now save the file and restart NTP service www.educlash.com

HOW TO GET NTP STARTED To get NTP configured to start at boot, use the line: [root@bigboy tmp]# chkconfig ntpd on To start, stop and restart NTP after booting, follow these examples: [root@bigboy tmp]# service ntpd start [root@bigboy tmp]# service ntpd stop [root@bigboy tmp]# service ntpd restart Doing An Initial Synchronization ntpdate command is run three times to synchronize smallfry's clock to server 192.168.1.100, but it must be run while the ntpd process is stopped [root@smallfry tmp]# ntpdate -u 192.168.1.100 7 www.educlash.com

PROVIDING A CACHING PROXY SERVER In computer networks, a proxy server is a server (a computer system or an application) that acts as an intermediary for requests from clients seeking resources from other servers. www.educlash.com

A PROXY SERVER HAS A VARIETY OF POTENTIAL PURPOSES, INCLUDING keep machines behind it anonymous, mainly for security speed up access to resources block undesired sites log / audit usage, Internet filtering to access content scan transmitted content for malware before delivery www.educlash.com

TYPES OF PROXY Forward proxy A forward proxy server will first check to make sure a request is valid. If a request is not valid, or not allowed (blocked by the proxy). If it is, the forward proxy serves the cached information. If it is not, the request is sent through a firewall to an actual content server which serves the information to the forward proxy. 10 www.educlash.com

Reverse proxy A reverse proxy is another common form of a proxy server and is generally used to pass requests from the Internet, through a firewall to isolated, private networks. It is used to prevent Internet clients from having direct, unmonitored access to sensitive data If caching is enabled, a reverse proxy can also lessen network traffic by serving cached information One advantage of using a reverse proxy is that Internet clients do not know their requests are being sent to and handled by a reverse proxy server www.educlash.com

Reverse proxy www.educlash.com

Proxy chaining A proxy chain uses two or more proxy servers to assist in server and protocol performance and network security. Proxy chaining is not a type of proxy, but a use of reverse and forward proxy servers across multiple networks. www.educlash.com

Proxy chaining www.educlash.com

SQUID WEB PROXY The Squid Web Proxy Cache is a fully featured Internet caching server that handles all types of web requests on behalf of a user. When a user requests a web resource (webpage, movie clip, graphic, etc..), Their request is sent to the caching server which then forwards the request to the real web server on their behalf. When the requested resource is returned to the caching server, it stores a copy of the resource in its "cache" and then forwards the request back to the original user. Using a proxy server can greatly reduce web browsing speed if frequently visited sites and resources are stored locally in the cache. www.educlash.com

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