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					SUSE Linux Enterprise Server
Administration (Course 3037)


             Chapter 7
 Connect the SUSE Linux Enterprise
      Server to the Network
                        Objectives

• Configure Your Network Connection
• Configure and Manage Routes
• Test the Network Interface




SUSE Linux Enterprise Server Administration (Course 3037)   2
  Configure Your Network Connection

• Objectives
   –   TCP/IP Fundamentals
   –   Network Interfaces in Linux
   –   Network Interface Requirements
   –   How to Configure a Network Card with YaST
   –   How to Modify a Network Card Manually




SUSE Linux Enterprise Server Administration (Course 3037)   3
              TCP/IP Fundamentals
• TCP/IP network components
   – Host
       • Receives requests for information from the Internet
   – TCP/IP
       • Defines how packets should be structured
   – IP packet
       • Electronic package of data sent over the Internet
   – Router
       • Forwards an IP packet to the next network point
   – Firewall
       • Protects the resources of a private intranet or network

SUSE Linux Enterprise Server Administration (Course 3037)          4
    TCP/IP Fundamentals (continued)

• IP address structure
   – Host is also referred to as a node or station
       • Routers locate hosts based on their IP addresses
   – IP address consists of four bytes:
       • A network address (from 1 to 3 bytes)
       • A node or station address (from 1 to 3 bytes)
   – Node address 0, and 255 are reserved
   – IP addresses take the form of a dotted octet
       • Each byte is separated by a dot


SUSE Linux Enterprise Server Administration (Course 3037)   5
    TCP/IP Fundamentals (continued)




SUSE Linux Enterprise Server Administration (Course 3037)   6
    TCP/IP Fundamentals (continued)




SUSE Linux Enterprise Server Administration (Course 3037)   7
    TCP/IP Fundamentals (continued)




SUSE Linux Enterprise Server Administration (Course 3037)   8
    TCP/IP Fundamentals (continued)

• Network classes and IP addresses
   – There are five address classes defined in IP
       • Classes A through C can be assigned
       • Classes D and E are reserved
   – Class A addresses
       • Networks: 126
       • Hosts per network: 16,777,216
   – Class B addresses
       • Networks: 16,384
       • Hosts per network: 65,534


SUSE Linux Enterprise Server Administration (Course 3037)   9
    TCP/IP Fundamentals (continued)




SUSE Linux Enterprise Server Administration (Course 3037)   10
    TCP/IP Fundamentals (continued)




SUSE Linux Enterprise Server Administration (Course 3037)   11
    TCP/IP Fundamentals (continued)

• Network classes and IP addresses
   – Class C addresses
       • Networks: 2,097,152
       • Hosts per network: 255
   – Class D addresses
       • First byte is in the 224 to 239 range
       • Used for multicast packets
   – Class E addresses
       • First byte is in the 240 to 255 range
       • Reserved for experimental use

SUSE Linux Enterprise Server Administration (Course 3037)   12
    TCP/IP Fundamentals (continued)

• Special IP addresses
   – See Table 7-1




SUSE Linux Enterprise Server Administration (Course 3037)   13
    TCP/IP Fundamentals (continued)




SUSE Linux Enterprise Server Administration (Course 3037)   14
          Network Interfaces in Linux

• Network interfaces
   – Always referred to with a fixed name
   – Name depends on type and position of the network
     card in the computer
       • First card is called eth0, second is eth1, and so on
• Drives
   – Provide support for network cards and protocols
   – Kernel modules that can be loaded if required
• SUSE Linux Enterprise Server
   – Contains drivers for all common network cards

SUSE Linux Enterprise Server Administration (Course 3037)       15
     Network Interface Requirements

• Network card is detected during installation
   – And a suitable driver is loaded
• Command ifstatus device
   – Verifies network card has been integrated correctly
       • With the appropriate driver
• Kernel support implemented as a module
   – Name of the module is entered by YaST
       • In a file in /etc/sysconfig/hardware/
• Drivers are autodetected for hotplug cards
   – No configuration is necessary
SUSE Linux Enterprise Server Administration (Course 3037)   16
How to Configure a Network Card with
               YaST
• Steps
   – Start the YaST Network Card module
   – Select a network card from the list (conditional)
   – Modify network card settings (conditional)




SUSE Linux Enterprise Server Administration (Course 3037)   17
How to Configure a Network Card with
         YaST (continued)




SUSE Linux Enterprise Server Administration (Course 3037)   18
How to Configure a Network Card with
         YaST (continued)




SUSE Linux Enterprise Server Administration (Course 3037)   19
How to Configure a Network Card with
         YaST (continued)




SUSE Linux Enterprise Server Administration (Course 3037)   20
How to Configure a Network Card with
         YaST (continued)
• Steps
   – Do one of the following
       • Add a new network card configuration
       • Modify an existing configuration
       • Delete a listed configuration
   – Select Next
   – Save the configuration by selecting Finish
   – Check network card activation and settings
       • From the command line using ifconfig or ip


SUSE Linux Enterprise Server Administration (Course 3037)   21
How to Configure a Network Card with
         YaST (continued)




SUSE Linux Enterprise Server Administration (Course 3037)   22
How to Configure a Network Card with
         YaST (continued)




SUSE Linux Enterprise Server Administration (Course 3037)   23
How to Configure a Network Card with
         YaST (continued)




SUSE Linux Enterprise Server Administration (Course 3037)   24
       How to Modify a Network Card
                Manually
• Configure the network interface with ifconfig
   – ifconfig (/sbin/ifconfig)
       • Used to manually configure a network card
       • Display information about status of network interfaces
   – Changes done with ifconfig are temporary
   – Syntax
       • ifconfig [interface] [address] [options]
   – ifconfig eth0 192.168.0.1
       • Assigns 192.168.0.1 to network card eth0
   – ifconfig eth0 up
       • Activates eth0
SUSE Linux Enterprise Server Administration (Course 3037)     25
       How to Modify a Network Card
          Manually (continued)




SUSE Linux Enterprise Server Administration (Course 3037)   26
       How to Modify a Network Card
          Manually (continued)
• Configure IP aliases with ifconfig
   – IP aliases
       • Used to define more than one IP address for a network
         card
   – It is always better to use genuine addresses
   – Configure an IP alias with ifconfig or YaST
   – View IP aliases by entering ip address show




SUSE Linux Enterprise Server Administration (Course 3037)   27
       How to Modify a Network Card
          Manually (continued)
• Modify network interface configuration files
   – Configuration files directory
       • /etc/sysconfig/network/
       • Contains file for each configured network adapter
   – Network interfaces are activated at boot
       • By script /etc/init.d/network
   – /etc/sysconfig/network/config
       • Contains general variables for the script
   – Directory /etc/sysconfig/network/scripts/
       • Contains additional scripts run by /etc/init.d/network

SUSE Linux Enterprise Server Administration (Course 3037)         28
       How to Modify a Network Card
          Manually (continued)
• Modify network interface configuration files
   – Activating and deactivating network interfaces
       • Use commands /sbin/ifup, /sbin/ifdown, /sbin/ifstatus
       • Use script /etc/init.d/network
• Configure host and domain names
   – Modify the following files
       • /etc/HOSTNAME
       • /etc/resolv.conf




SUSE Linux Enterprise Server Administration (Course 3037)        29
        Configure and Manage Routes

• Objectives
   –   Route Types
   –   How to Manage Routes with route
   –   How to Modify Route Configuration Files
   –   How to Activate Routing
   –   How to Manage the Network Interface and Routes
       with ip




SUSE Linux Enterprise Server Administration (Course 3037)   30
                       Route Types
• Host routes
   – Define path data packet can take for exactly one
     destination host
• Network and gateway routes
   – Define path data packet can take for an entire
     destination network
• Default route
   – Special gateway route
   – Defines route data packet can take if no previous
     route matched destination of the packet

 SUSE Linux Enterprise Server Administration (Course 3037)   31
    How to Manage Routes with route

• Use command route (/sbin/route)
   – To check and edit the routing table
• Create a route
   – Syntax
       • route add [-net | -host destination] [netmask mask] [gw
         gateway] [metric n] [dev interface]
   – Static routing is set up by default
   – Dynamic routing needs a routing daemon
       • You also need to add the option metric n


SUSE Linux Enterprise Server Administration (Course 3037)     32
    How to Manage Routes with route
             (continued)
• Delete a route
   – Syntax
       • route del [-net | -host destination] [gw gateway]
         [netmask mask] [dev interface]
   – route del default
       • Deletes the default route




SUSE Linux Enterprise Server Administration (Course 3037)    33
   How to Modify Route Configuration
                 Files
• An entry is generated in the kernel routing table
   – For all active network interfaces
• Additional static routes
   – Configured in the files
        • /etc/sysconfig/network/routes
        • /etc/sysconfig/network/ifroute-Interface
• Configuration files include the following fields:
   –   Destination network/destination host
   –   The gateway to use
   –   The network mask
   –   The network interface
SUSE Linux Enterprise Server Administration (Course 3037)   34
            How to Activate Routing

• A Linux host can also serve as a router itself
   – This property is deactivated by default
• Activate routing by adding entry in the process file
   – echo 1 > /proc/sys/net/ipv4/ip_forward
   – 0 will deactivate routing
• Activate routing permanently
   – Set following variable in /etc/sysconfig/sysctl
       • IP_FORWARD=“yes”



SUSE Linux Enterprise Server Administration (Course 3037)   35
 How to Manage the Network Interface
         and Routes with ip
• SUSE Linux Enterprise Server ip command
   – Replaces ifconfig and route commands
• ip general syntax
   – ip [options] object [command [parameters]]
• Modifications made with command ip are temporary
• Tasks performed with ip:
   – Assign Parameters for Network Interfaces (ip link)
   – Assign IP Addresses (ip address)
   – Set Up Routes (ip route)

SUSE Linux Enterprise Server Administration (Course 3037)   36
How to Manage the Network Interface
  and Routes with ip (continued)




SUSE Linux Enterprise Server Administration (Course 3037)   37
 How to Manage the Network Interface
   and Routes with ip (continued)
• Assign Parameters for Network Interfaces (ip link)
   – Use ip commands
       • set and show
• Assign IP Addresses (ip address)
   – Most important ip commands
       • add, del, and show
• Set Up Routes (ip route)
   – Use ip commands
       • add, change, delete, and show


SUSE Linux Enterprise Server Administration (Course 3037)   38
How to Manage the Network Interface
  and Routes with ip (continued)




SUSE Linux Enterprise Server Administration (Course 3037)   39
How to Manage the Network Interface
  and Routes with ip (continued)




SUSE Linux Enterprise Server Administration (Course 3037)   40
How to Manage the Network Interface
  and Routes with ip (continued)




SUSE Linux Enterprise Server Administration (Course 3037)   41
          Test the Network Interface

• Objectives
   – Check a Network Connection between Hosts (ping)
   – Check the Routing (traceroute)
   – Analyze Network Traffic (tcpdump and ethereal)
   – Determine the Status of All Network Connections
     (netstat)
   – Check for Service Availability (netcat)




SUSE Linux Enterprise Server Administration (Course 3037)   42
Check a Network Connection between
           Hosts (ping)
• Command ping (/sbin/ping)
   – Simple tool for checking network connections
• How the command tests a connection
   – Enter ping host
   – Server sends ICMP datagram to the target host
       • With the echo request
   – Target host answers with ICMP datagram
       • Containing the message echo reply
   – ICMP protocol does not involve higher level protocols
• Command options
   – See Table 7-7
SUSE Linux Enterprise Server Administration (Course 3037)   43
Check a Network Connection between
      Hosts (ping) (continued)




SUSE Linux Enterprise Server Administration (Course 3037)   44
Check a Network Connection between
      Hosts (ping) (continued)
• Troubleshooting suggestions
   – Start by checking the host-internal network
       • ping localhost
   – Then check network interface connected to your host
       • ping interface_addr
   – Check network segment to the next closest network
     element
       • In the direction of the target host
       • Until the check ends at the target host



SUSE Linux Enterprise Server Administration (Course 3037)   45
      Check the Routing (traceroute)

• Command traceroute (/usr/sbin/traceroute)
   – Helps you follow route taken by an IP datagram
• How a route is traced
   – traceroute sends three UDP datagrams with TTL = 1
   – Then increases value for the next three datagrams
   – TTL is reduced by 1 when UDP datagram passes
     through a router
       • Datagram is discarded at TTL=0
   – Gateway at TTL=0 sends an ICMP datagram
       • With message “TTL exceeded” back to the sender

SUSE Linux Enterprise Server Administration (Course 3037)   46
      Check the Routing (traceroute)
               (continued)
• How a route is traced
   – If UDP datagram reaches the target host
       • Host replies with ICMP datagram Port Unreachable
   – From this message
       • Sender recognizes that target host has now been
         reached
   – Syntax
       • traceroute host
• Command options
   – See Table 7-8
SUSE Linux Enterprise Server Administration (Course 3037)   47
      Check the Routing (traceroute)
               (continued)




SUSE Linux Enterprise Server Administration (Course 3037)   48
      Check the Routing (traceroute)
               (continued)
• Troubleshooting suggestions
   – Common reason for defective communication
       • Transport path between these networks contains errors
   – traceroute
       • Excellent tool for checking routers located on this
         transport path
       • Shows at which hop the transport path is faulty




SUSE Linux Enterprise Server Administration (Course 3037)      49
Analyze Network Traffic (tcpdump and
             ethereal)
• How to use tcpdump
   – Command tcpdump (/usr/sbin/tcpdump)
       • Lets you analyze data packets
   – Syntax
       • tcpdump –i interface
           – Puts interface in promiscuous mode
• How to use ethereal
   – Graphical tool
   – Provides the same functionality as tcpdump
   – Must be first installed using YaST
SUSE Linux Enterprise Server Administration (Course 3037)   50
Analyze Network Traffic (tcpdump and
        ethereal) (continued)




SUSE Linux Enterprise Server Administration (Course 3037)   51
Analyze Network Traffic (tcpdump and
        ethereal) (continued)




SUSE Linux Enterprise Server Administration (Course 3037)   52
Analyze Network Traffic (tcpdump and
        ethereal) (continued)
• Command options (tcpdump)
   – See Table 7-9
• Troubleshooting suggestions
   – Use tcpdump or ethereal to analyze network traffic
   – Helps you find which packets are exchanged
   – Recommended for security-critical environments




SUSE Linux Enterprise Server Administration (Course 3037)   53
  Determine the Status of All Network
        Connections (netstat)
• Command netstat (/bin/netstat)
   – Helps you determine the status of all network
     connections on a host
• How to use netstat
   – Displays the status of all open sockets
   – Information is displayed in two blocks
       • First block
           – Each socket is listed on a separate line
       • Second block
       • Contains information on the UNIX domain sockets
         active on the host
SUSE Linux Enterprise Server Administration (Course 3037)   54
  Determine the Status of All Network
   Connections (netstat) (continued)
• Command options
   – See Table 7-10
• Troubleshooting suggestions
   – netstat
       • Ideal for monitoring resources for network sockets on a
         host
       • Provides detailed information on existing and available
         network sockets or resources




SUSE Linux Enterprise Server Administration (Course 3037)    55
  Determine the Status of All Network
   Connections (netstat) (continued)




SUSE Linux Enterprise Server Administration (Course 3037)   56
 Check for Service Availability (netcat)
• Command netcat (/usr/bin/netcat)
   – Uses TCP and UDP protocols
       • To read and write data through network connections
• How to use netcat
   – netcat host port
• Advanced use of netcat
   – Query ports and display the responses of the services
   – nmap command
       • More suitable for a simple port scan
   – Transmit files between hosts
• Command options (see Table 7-11)

SUSE Linux Enterprise Server Administration (Course 3037)     57
 Check for Service Availability (netcat)
             (continued)




SUSE Linux Enterprise Server Administration (Course 3037)   58
Exercise 7-1: Configure and Test Your
         Network Connection
• In this exercise, you do the following:
   – Part I: View and Record Network Configuration
   – Part II: Configure a Static Network with YaST
   – Part III: Test the Network Card Configuration




SUSE Linux Enterprise Server Administration (Course 3037)   59
                        Summary
• Each host has an IP address and subnet mask
• IP classes normally used for IP addressing
  – Class A, B, and C
• Commands ifconfig and ip
  – View and change your TCP/IP configuration
• Network interface and TCP/IP information
  – Stored in the /etc/sysconfig/network
  – Started by the /etc/init.d/network script
• Each host contains a hostname
  – Stored in the /etc/HOSTNAME file
SUSE Linux Enterprise Server Administration (Course 3037)   60
               Summary (continued)

• /etc/resolv.conf file
   – Contains the addresses of up to three DNS servers
• TCP/IP networks are connected via routers
   – Host has a routing table
       • That typically contains a default gateway route
• Commands route and ip
   – View and change the routing table
• Commands ping and traceroute
   – Used to test network communication and routing


 SUSE Linux Enterprise Server Administration (Course 3037)   61
               Summary (continued)

• Command netcat
   – Used to test TCP and UDP connections
• Utilities tcpdump and ethereal
   – Used to capture and analyze network traffic




 SUSE Linux Enterprise Server Administration (Course 3037)   62

				
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