SUSE Linux Enterprise Server Administration (Course 3037) Chapter 7 Connect the SUSE Linux...

SUSE Linux Enterprise Server Administration (Course 3037)

Chapter 7Connect the SUSE Linux Enterprise

Server to the Network

SUSE Linux Enterprise Server Administration (Course 3037) 2

Objectives

• Configure Your Network Connection

• Configure and Manage Routes

• Test the Network Interface

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

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

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

• 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

• 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

• Special IP addresses– See Table 7-1

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

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

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)

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

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

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

• 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

• 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

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

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

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

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

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

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”

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)

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

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)

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

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

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

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

• 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

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

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

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

Determine the Status of All Network Connections (netstat) (continued)

• Troubleshooting suggestions– netstat

• Ideal for monitoring resources for network sockets on a host

• Provides detailed information on existing and available network sockets or resources

Determine the Status of All Network Connections (netstat) (continued)

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)

Check for Service Availability (netcat) (continued)

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

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

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

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) Chapter 7 Connect the SUSE Linux...

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