Linux: Networking

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LinuxNetworking Security

• Feng Gao
• 104504
• 2000-08-31

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Objective (1)

• Give an overview of the networking capacities of
  the Linux OS
• Networking protocols
• Capacity for file sharing printing
• Capacity for Internet/Intranet services
• Capacity for remote execution of application
• Capacity for acting as network interconnection
• Capacity for network management

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Objective (2)

• Talk about some security tools for Linux network
• Monitoring tools
• Network services
• System integrity
• Management limitation

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Brief Introduction of Linux OS

• A Unix like operating system
• Completely open source code
• no royalty or licensing fees
• the source code can be modified to fit users
  needs
• Fast, powerful, and extremely stable
• Cross hardware and platform
• Tons of application software
• Created by and for the Internet

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Why Linux is a choice for network

• Cheap portable
• Ideal for many small to medium businesses
• Open source code
• Tons of applications are freely available
• Modifiable whenever/wherever needed
• Robustness

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Who uses Linux?
Besides ISPs and other Web companies, the
following companies had some Linux servers
installed in 1997.

• Ford Motor Co.
• NASA
• Disney
• General Electric
• IRS

• UPS
• NASDAQ
• Boeing
• many leading US Universities

Used for gateways, routers, file and print
servers, database servers, computation servers,
development servers, CAD, besides being used as
Web servers.
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Part I

• Linux Networking

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Network protocols supported by Linux

• TCP/IP
• IPv6 ( IP version 6 )
• IPX/SPX
• AppleTalk Protocol
• WAN networking Protocols
• Isdn4linux
• PPP, SLIP, PLIP
• ATM
• More ???

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File sharing and printing

• Sharing with Apple environment
• using AppleTalk family protocols ( NetaTalk)
• Sharing with Windows environment
• using Samba ( an implementation of SMB protocol)
• Sharing with Novell environment
• using IPX/SPX
• Sharing with Unix environment
• using NFS ( Network File system)

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Internet / Intranet services

• Mail
• Mail Servers ( eg.Sendmail, smail, qmail, etc.)
• Remote access to mail (POP, IMAP)
• Fetchmail
• Web Servers
• Apache
• Stable, Robust
• Yahoo, Altavista, Geocities, Hotmail are based on
  this server

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Internet/Intranet services (cont)

• Web Browsers
• Netscape Navagator, Mozilla , lynx, etc.
• FTP servers clients
• News service
• Domain Name System ( DNS )
• NIS ( Network Information Service )

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Remote execution of application

• Telnet
• Use a remote computer as if just at the site
• Remote commands
• Execution of a command on a remote machine
• The X window system
• The X server controls the display and I/O
• The X client do the real computing work
• VNC ( Virtual Network Computing)
• eg. Execute in a Windows machine and output
  displayed in a Linux machine

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Acting as Network Interconnection

• Bridge
• Router
• Firewall
• Proxy Server
• IP Masquerade

• Load Balancing
• Traffic Shaping
• Port Forwarding
• Virtual private networks

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Network Management

• Network management applications
• Webmin
• Linuxconf
• SNMP (Simple Network Management Protocol )
• allows for remote monitoring and configuration of
  routers, bridges , network cards, switches

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Part II

• Security tools
• for Linux network

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Monitoring tools

• Scan to determine if the machine is vulnerable to
  a specific exploit on that server
• Connect to target machine on all ports they can
• Help to fix the found problems
• Examples
• SATAN ( Security Administrators Tool for
  Analyzing Networks )
• ISS( Internet Security Scaner )
• SAINT ( updated version of SATAN )
• Nessus, xSid, Logcheck, PortSentry

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Network Services

• Problem
• The more services the system offers, the more
  places for attackers to find a hole

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Network Services (cont)

• Strategy
• Disable or remove services not needed
• Use tcp_wrappers to wrap all the TCP services
• Use SSH to replace old, insecure remote programs
  such as telnet, rlogin, rdist, rcp
• SSH
• A secure login program that revolutionized remote
  management of networks hosts over the Internet
• A powerful program that uses strong cryptography
  for protecting all transmitted confidential data

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System integrity

• Problem
• A typical Linux server handles about 30,400
  files
• In its busy times administrators cant check the
  integrities of all system files
• A cracker can easily install or modify some files

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System Integrity ( cont )

• Security tools
• Tripwire
• Tripwire ASR ( Academic Source Release )

Create a database first ? Check the integrity of
a system at any time ? Compare the current system
and the stored database ? Find if malicious
changes exist
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Management Limitation

• GnuPG
• A tool for secure communication and data storage
• Can be used to encrypt data and create digital
  signatures
• Quota
• A system administration tool for monitoring and
  limiting users and groups disk usage
• With quota, the users are forced by the system
  administrator to not consume unlimited disk space
  on a system

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Summary
Weve talked about

• The network capacities of Linux OS
• Support of many network protocols
• File sharing and printing
• Internet / Intranet Services
• Remote execution of application
• Acting as network interconnection
• Network managemet

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Summary
Also talked about

• Some security tools for Linux network
• Monitoring tools
• Network services
• System integrity
• Management Limitation