1. LINUX ADMINISTRATION

2. UNIT 4
CHAPTER-1

3. CHAPTER 1 : INTERNET SERVICES
WHAT IS AN INTERNET SERVICE?
Internet Service can be defined as any service that can be accessed through TCP/IP based networks, whether an internal network (Intranet) or external network (Internet)
Internet services can be provided through either secure or non-secure TCP/IP connections.
Common services are Telnet, FTP, SMTP, HTTP, ICMP, ARP, DNS, ssh, scp, sftp, and others.

4. Secure Services Plain text traffic is extremely easyto eavesdrop on by
anyone
Since the Internet has exploded in popularity, running insecure services such as these is not a good idea.
That‘s why secure replacements have been developed
These replacements provide stronger Authentication controls and encrypt all their traffic to keep your data safe.

5. Ssh
Secure Shell, also known as ssh, is a secure telnet replacement that encrypts all traffic, including passwords, using a public/private encryption key exchange protocol.
ssh
you start ssh, it asks for your password, and then you have a regular terminal screen.

6. scp Secure Copy, also known as scp, is part of the ssh package.
It is a secure alternative to rcp and ftp
You can scp files to any machine that has an ssh daemon running

7. sftp
Secure File Transfer Program, also known as sftp, is an FTP client that performs all its functions over ssh.
The syntax for sftp is
sftp file

8. Less Secure Services telnet
These are insecure services that should not be used, since they trust that the network is absolutely secure.
telnet
Telnet is an application that‘s available almost
everywhere.
All telnet traffic, including passwords, is sent in plain text.
vnavrat]$ telnet xena
 Trying
Connected to xena.
Escape character is ‘^]’.
Welcome to null.xena.edu
login:

9. Rsync Rsh rlogin Finger
rsync is an unencrypted file transfer program that is similar to rcp.
Differences between two sets of files on two machines to be transferred across the network.
Rsh
rsh is an unencrypted mechanism to execute commands on remote hosts.
rsh remotehostname remotecommand
rlogin
rlogin is a remote login program that connects your
terminal to a remote machine‘s terminal.
Finger
finger enables users on remote systems to look up information about users on another system.
Generally finger displays a user‘s login name, real name, terminal name, idle time, login time, office location, and phone number.

10. talk and ntalk Talk and ntalk are real-time chat protocols.
The talk server runs on port 517
The ntalk server runs on port 518.

11. USING YOUR LINUX MACHINE AS A SERVER
http
The most common Web server used on Linux is Apache
configuration files live in /etc/httpd/conf/.
Sshd
The secure shell daemon (sshd) is started out of the
system‘s rc scripts.
global system configuration files are in /etc/ssh
user‘s ssh configuration files are in $HOME/.ssh/.

12. Ftpd dns The FTP daemon uses ports 20 and 21 to listen for
and initiate FTP requests
Its configuration files
ftpaccess
ftpconversions
ftpgroups
ftphosts
ftpusers
located in the /etc directory.
dns
The Domain Name Service (DNS), which maps IP addresses to hostnames,
It is served by the named program on port 53.
Its configuration file is named.conf in the /etc directory. 12

13. The Inetd Server Xinetd inetd is called an Internet superserver.
It is launched at boot time, and listens for
connections on network sockets.
It checks the inetd.conf file to see what services should be running.
It then reads the /etc/services file to see what ports those services should be running on.
Xinetd
xinetd is a replacement for inetd, that adds more security and functionality.
great reason to run xinetd is that it can run alongside inetd
inetd and xinetd behave the same way

14. INETD AND XINETD

15. SERVICES ARE SPAWNED FROM SUPERSERVERS
SUCH AS INETD AND XINETD
1. chargen — random character generator that sends its traffic over tcp
2. daytime-udp — gives you the time over udp
3. finger — user information lookup program
4. kshell — restricts user access to the shell
5. rlogin — service similar to telnet, but enables trust relationships between machines
6. swat — Samba Web Administration Tool
7. time — gives you the time
8. chargen-udp — random character generator that sends its traffic over udp
9. echo — echoes back all characters sent to it over tcp
 10. gssftp — kerberized FTP server

16. www.educlash.com 11. rsh — remote shell
12. talk — a talk (real-time chat) server
13. time-udp — gives you the time over udp
14. comsat — notifies users if they have new mail
15. echo-udp — echoes back all characters sent to it over udp
16. klogin — kerberos‘s answer to rlogin
17. ntalk — a talk (real-time chat) server
18. rsync — remote file transfer protocol
19. telnet — telnet server
20. wu-ftpd — an ftp server
21. daytime — gives you the time over tcp
 22. eklogin — encrypting kerberized rlogin server

17. www.educlash.com 23. krb5-telnet — kerberized telnet server
24. rexec — provides remote execution facilities
25. sgi_fam — file monitoring daemon
26. tftp — trivial file transfer program

18. STAND-ALONE SERVICES
These services are started from the rc scripts specifically written for them in the rc directories.
You can enable or disable these services from those directories.

19. www.educlash.com 1. apache — Web server 2. sshd — ssh server
3. sendmail — mail server
4. qmail — mail server
5. postfix — mail server
6. thttpd — semilightweight Web server
7. boa — lightweight Web server
8. named — dns server
9. xfs — X font server
10. xdm — X display manager

20. 11. portmap — maps RPC services to ports
12. rpc.quotad — serves quota information
13. knfsd — userspace portion of the NFS daemon
14. rpc.mountd — NFS mount server
15. rpc.ypbind — NIS server
16. squid — Web proxy server
17. nessusd — penetration testing server
18. postgresql — database server
19. mysql — database server
 oracle — database server 20

21. LINUX FIREWALL PACKAGES
Linux provides a few different mechanisms for system security. One of these mechanisms is Linux‘s firewall packages.
Two of the firewalling packages available are tcp- wrappers and ipchains.
tcp-wrappers is a minimalistic packet filtering
application to protect certain network ports
ipchains is a packet filtering firewall.

22. TCP wrappers works only on programs that are started from inetd.
An inetd.conf without tcp-wrappers would look like this:
telnet stream tcp nowait root /usr/sbin/in.telnetd in.telnetd
An inetd.conf with tcp-wrappers looks like this:
telnet stream tcp nowait root /usr/sbin/tcpd in.telnetd

23. WHAT DOES WITH AND WITHOUT WRAPPER
MEANS
If your system does not have TCP Wrappers built in
your configuration will have to use the tcpd program that is part of TCP Wrappers to wrap inetd services.
In order to wrap an inetd service.you simply change its entry in /etc/inetd.conf so that tcpd is executed
telnet stream tcp nowait root /usr/sbin/in.telnetd in.telnetd telnet stream tcp nowait root /usr/sbin/tcpd in.telnetd
In other words, replace the pathname of the daemon with the full path to tcpd, leaving everything else untouched. 23

24. If the hostname is in /etc/hosts.deny, the connection is closed.
When inetd starts up, it looks through /etc/inetd. to see what network service connections it should start listening for.
tcpd is then called and reads the /etc/hosts.allow file to see if the hostname is allowed.
If the hostname is in /etc/hosts.deny, the connection is closed.

25. SYNTAX OF AN ALLOW OR DENY RULE
service: hostname : options
Add rules host.allow or in host.deny
hosts.allow file
in.telnetd: .xena.edu : ALLOW
To enable only machines from the xena.edu domain to telnet into your machine
hosts.deny file
in.telnetd: .xena.edu : DENY

26. ipchains is Linux‘s built-in IP firewall administration tool
Using ipchains enables you to run a personal firewall to protect your Linux machine.
If the Linux machine is a routing gateway for other machines on your network, it can act as a packet filtering network firewall if more than one network interface is installed.

27. THANK YOU