1. Linux Server Administration
Most Popular Server Operating System
CentOS
RedHat
Microsoft Windows Server
Fedora
Ubuntu

2. Telnet
Bi-directional interactive text-oriented communication
facility using a virtual terminal.

Port 23(TCP).

Client-Server Architecture
Vulnerability:
Plain text sent over the connection

No authentication to ensure connection between
two desired hosts.

3. Secure Shell(SSH)

Cryptographic Network Protocol.

Secure data-communication.

Remote Command execution.

Cipered text(encrypted) is sent over the connection.

Port 22(TCP)
Applications:

Secure Access to shell Accounts.

4. File Transfer Protocol(FTP)

Transfer files from one host to another.

Client-serverArchitecture.

Port 20(Data-channel)

Port 21(Client-Server)
Vulnerability:

Brute Force Attacks

Packet Capture(Sniffing).

Spoof Attacks.

5. Domain Name Service(DNS)

Hierarchical distributed naming system for devices
on internet or on the private network.

Translates domain name to IP Addresses and vice-
versa.

Port 53(UDP).

Zones:

Forward Zone-Translates Name to its IP.

Reverse Zone-Translates IP to its Name.

6. Domain Name Service(DNS)
Common Keywords:

A-Address records

NS-Nameserver records

MX-Mail Exchanger records.
Vulnerabilities:

DNS Cache Poisoning.

DNS Spoofing.

7. Dynamic Host Configuration
Protocol(DHCP)

Dynamically Distributes IP for interaces and
services.
Operations(DORA):

DHCP Discover.

DHCP Offer.

DHCP Request.

DHCP Acknowlegement.
Features:

Periodic Renewal,Rebinding,Failover Mechanisms.

8. Dynamic Host Configuration
Protocol(DHCP)
Port 67(Connection to Server).
Port 68(Connection to Client).
Types of Allocations:

Static ,Dynamic and Automatic.
Vulnerabilites:

No way to validate Identity of DHCP Server.

Resource Exhaustion Attacks from malicious DHCP
Clients.

9. Apache Web Server

Most Popular Web Server(Worldwide).

Can be implemented on all OS'es.

Port 80(HTTP),443(HTTPS).

Support compiled modules(mod_ssl,mod_status).

Support Virtual Hosting.

Support Web Authentication Mechanisms.

Supports PHP,Perl,HTML,other web-based
languages.

10. Apache Web Server
Vulnerabilities:

SQL Injection.

Cross Site Scripting(XSS).

DOS Attacks.

11. Server Message Block(SMB)

File and Printer Services for Windows Clients.

Primary Domain Controller for Windows Clients.

Encrypted Data communication by default.
Protocol NetBios-
NameService(ns)
NetBios-
Datagram(dgm)
NetBios-
Session(ssn)
Active
Directory(ad)
Port No. 137(UDP,TCP) 138(UDP) 139(TCP) 445(TCP)

12. Postfix Webmail Server

Mail Transfer agent that routes and deliver emails.

MIME Encapsulation,SASL Authentication.

Delivery Status Notifications(DSN).

Port 25(SMTP).
Features:

Defense against malware and spambots.

Combines with Message storage access(Dovecot).

Provides GUI with Squirrel(Web-based email
Client).

13. Proxy Server

Intermediate between the Client and Originial
Server.
Advantages:

Monitoring and filtering.

Improves Caching,Performance and Load
Balancing.

Protect the Actual Server from Attacks.

Spoon Feeding to Slow Clients.

Accessing services anonymously.

14. Proxy Server
Types of Proxies:

Tunneling Proxies.

Forwarding Proxies.

Reverse Proxies.
Examples:

Socks Proxy.

Squid Proxy Server(Port 3128).

15. Linux Security

Apache Web Based Authentication.

Cryptography.

Sudoers.

Access Control Lists(ACL).

Secured Enhanced Linux.

Firewall.

16. Web based Authentication

Permitted Users have access to Critical Directory.

Authentication Required.

17. Cryptography

Converts Plain text to Ciphered text.

Confidentiality,Integrity,Accuracy.

SSL Security with Apache(port 80/HTTPS).
Mechanisms-

Encryption -plain to ciphered text.

Decryption-ciphered to plain text.

18. Cryptography
Types
Encryption:

AES-128,192,256 bit keys,block size 128
bits,highly secured.

DES-56 bit keys,block size of 64 bits,Less Secured.
Cryptogaphy Advantages Security No. of Keys Alias Name
Symmetic Key Simpler and
Faster.
Less Secured. 1 Key(Shared) Secret Key
Cryptography
Asymmetric Key More Secured
Authentication
Complex(Highly
Secured)
2 Keys(Public
,Private)
Public Key
Cryptography

19. Sudoers

Security Policy in Linux Architecture.
Users: Normal Users. Super Users.

Users can execute commands on behalf of super
users using 'sudo'.

Uses Caching.
Command:

User_alias Hostname_alias=(User_spec)
Cmnd_alias.

20. Access Control List(ACL)

Sets Different permissions to different users on the
same directory.

Grant Permissions to user,group even if they are not
belong to the actual group.
Types

Default ACL's-Setting ACL's on a specific
Directory.

Access ACL's-Granting permissions to any file or
Directory.

21. Secured Enhanced Linux(SELinux)

Linux Kernel Security Module.

Enforces minimum privileges to services to do their
jobs.

Helpful when Server is under Attack.
Types:

Permissive-access denied services can be operated
even if it is enabled.

Enforcing-enforces access denials to services.

Disabled-disables SELinux protection permanently.

22. Firewall