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Do the following steps as:

1.vi /etc/xinetd.d/telnet

service telnet {

only_from=192.168.0.0/24

access_times=09:00-17:00

}

2.chkconf telnet on

3.service xinetd restart

xinetd based services can manage by specifying host and time parameters. Only_from means connection allowed network, remaining hosts explicitly deny. access_times specify when service is available.

Do the following steps as:

1.vi /etc/hosts.deny

nfs,portmap:ALL EXCEPT .example.com, trusted.cracker.org

We can secure the services using tcp_wrappers. There are main two files, /etc/hosts.allow and /etc/hosts.deny.

There will be three stage access checking

-Is access explicitly permitted? Means permitted from /etc/hosts.allow?

- Otherwise, Is access explicitly denied? Means denied from /etc/hosts.deny?

- Otherwise, by default permit access if neither condition matched.

To deny the services we can configure /etc/hosts.deny file using ALL and EXCEPT operation. Pattern of /etc/hosts.allow and /etc/hosts.deny file is:

Demon_list:client_list:options

In Client list can be either domain name or IP address.

Do the following steps as:

1.vi /etc/hosts.deny

sshd: 192.168.0. EXCEPT 192.168.0.4

We can secure the services using tcp_wrappers. There are main two files, /etc/hosts.allow and /etc/hosts.deny.

There will be three stage access checking

-Is access explicitly permitted? Means permitted from /etc/hosts.allow?

- Otherwise, Is access explicitly denied? Means denied from /etc/hosts.deny?

- Otherwise, by default permit access if neither condition matched.

To deny the services we can configure /etc/hosts.deny file using ALL and EXCEPT operation. Pattern of /etc/hosts.allow and /etc/hosts.deny file is:

Demon_list:client_list:options

In Client list can be either domain name or IP address.

Do the following steps as:

1.vi /etc/hosts.deny

vsftpd:ALL EXCEPT .example.com

We can secure the services using tcp_wrappers. There are main two files, /etc/hosts.allow and /etc/hosts.deny.

There will be three stage access checking

-Is access explicitly permitted? Means permitted from /etc/hosts.allow?

- Otherwise, Is access explicitly denied? Means denied from /etc/hosts.deny?

- Otherwise, by default permit access if neither condition matched.

To deny the services we can configure /etc/hosts.deny file using ALL and EXCEPT operation. Pattern of /etc/hosts.allow and /etc/hosts.deny file is:

Demon_list:client_list:options

In Client list can be either domain name or IP address.

Do the following steps as:

1.vi /etc/samba/smb.conf

[global]

netbios name=station?

workgroup=station?

security=user

smb passwd file=/etc/samba/smbpasswd

encrypt passwords=yes

hosts allow= .example.com

[data]

path=/data

public=no

writable=no

browsable=yes

2.smbpasswd -a eric

3.service smb start

4.chkconfig smb on

/etc/samba/smb.conf. There are some pre-defined section, i. globaluse to define the global options, ii. Printersuse to share the printers, iii. homesuse the share the user’s home directory.

Security=uservalidation by samba username and password. May be there are other users also. To allow certain share to certain user we should use valid users option.

smbpasswdHelps to change user’s smb password. –a option specifies that the username following should be added to the local smbpasswd file.

Do the following steps as:

1.vi /etc/aliases

john:jane

2.newaliases

We can redirect the mail of one user to another user using /etc/aliases file. In example all mail of john goes to jane user. When you configure this line mail automatically goes to jane’s mail spooling directory.

Do the following steps as:

1.vi /etc/hosts.deny

in.telnetd:ALL EXCEPT 192.168.0.

We can secure the services using tcp_wrappers. There are main two files, /etc/hosts.allow and /etc/hosts.deny.

There will be three stage access checking

-Is access explicitly permitted? Means permitted from /etc/hosts.allow?

- Otherwise, Is access explicitly denied? Means denied from /etc/hosts.deny?

- Otherwise, by default permit access if neither condition matched.

To deny the services we can configure /etc/hosts.deny file using ALL and EXCEPT operation. Pattern of /etc/hosts.allow and /etc/hosts.deny file is:

Demon_list:client_list:options

In Client list can be either domain name or IP address. Here in.telnetd is the telnet server program name.

Do the following steps as:

1.iptables –t filter –A INPUT –s ! 192.168.0.0/24 –p tcp –d 192.168.0.254 --dport 20 –j DROP

2.iptables –t filter –A INPUT –s ! 192.168.0.0/24 –p tcp –d 192.168.0.254 --dport 21 –j DROP

iptables is the build-in firewall tools, used to filter the packets and for nat. By identifying Source Address, Destination Address, type of protocol, source and destination port we can filter the packets.

-sSource Address

-dDestination Address

-pLayer 3 Protocol

-dDestination Address

--sportSource Prot

--dportDestination Port

-iIncoming Interface

-oOutgoing Interface

-tTable either filter or nat or mangle

-AChain can be either INPUT, OUTPUT, FORWARD, PREROUTING, POSTROUTING.

IMAP is a very usefully protocol, but it lacks encryption. The dovecot package distributed with RHEL includes the ability to use IMAP over SSL, This requires the creation of a PEM format certificate.

cd /usr/share/ssl/certs

make dovecot.pem : Which generates the dovecot.pem certificate by reading MakeFile

Enable the imaps protocol from /etc/dovecot.conf

vi /etc/dovecot.conf

protocols = imap imaps

service dovecot restart : Restart the Dovecot service

Do the following steps as:

1.vi /etc/mail/local-host-names

example.com

2.vi /etc/mail/sendmail.mc

dnl # DEAMON_OPTIONS(`Port=smtp,Addr=127.0.0.1,Name=MTA`)dnl

3.m4 /etc/mail/sendmail.mc >/etc/mail/sendmail.cf

4.vi /etc/mail/access

192.168.0RELAY

@cracker.orgREJECT

5.service sendmail start | restart

6.chkconfig dovecot on

7.vi /etc/dovecot.conf

protocols = pop3 pop3s imap imaps

8.service dovecot start | restart

9.chkconfig dovecot on

10.vi /etc/aliases

user5:user2

11.newaliases

/etc/mail/local-host-names file contains the aliases to hostname. Mail server program reads the /etc/mail/sendmail.cf. To change the configuration on mail server, we should edit the /etc/mail/sendmail.mc file and should generate the sendmail.cf using m4 command.

By default sendmail server allows to connect to local host only. So we should edit the /etc/mail/sendmail.mc file to allow connect to other hosts.

By default sendmail server will not forward mail. we should specify on /etc/mail/access to relay or to block mail coming from domain or network or individual email address.

By default dovecot service start only the imap protocol. To start pop protocol with dovecot, we should write in /etc/dovecot.conf file.

Using /etc/aliases file we can map the user name to send mail of one user to another user. To rebuild database we use the newaliases command.