1. LINUX ADMINISTRATION 1

2. UNIT 3
CHAPTER-2 2

3. 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

4. HOW TO CONFIGURE NTP SERVICE
Download and Install The NTP Package
Download ntp 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.

5. 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 nomodify notrap noquery
restrict ntp.research.gov mask nomodify notrap noquery
Note: mask statement is really a subnet mask limiting access to the single IP address

6. 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 mask 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
It will give full access to localhost
5) now save the file and restart NTP service

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

8. 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.

9. 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

10. 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

11. 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

12. Reverse proxy

13. 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.

14. Proxy chaining

15. 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.

16. THANK YOU 16