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

SUSE Linux Enterprise Server Administration (Course 3037)3 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)4 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)5 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)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)

SUSE Linux Enterprise Server Administration (Course 3037)9 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)10 TCP/IP Fundamentals (continued)

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

SUSE Linux Enterprise Server Administration (Course 3037)12 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)13 TCP/IP Fundamentals (continued) Special IP addresses –See Table 7-1

SUSE Linux Enterprise Server Administration (Course 3037)14 TCP/IP Fundamentals (continued)

SUSE Linux Enterprise Server Administration (Course 3037)15 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)16 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)17 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)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)

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

SUSE Linux Enterprise Server Administration (Course 3037)25 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 eth Assigns to network card eth0 –ifconfig eth0 up Activates eth0

SUSE Linux Enterprise Server Administration (Course 3037)26 How to Modify a Network Card Manually (continued)

SUSE Linux Enterprise Server Administration (Course 3037)27 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)28 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)29 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)30 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)31 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)32 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)33 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)34 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)35 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)36 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)37 How to Manage the Network Interface and Routes with ip (continued)

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

SUSE Linux Enterprise Server Administration (Course 3037)42 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)43 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)44 Check a Network Connection between Hosts (ping) (continued)

SUSE Linux Enterprise Server Administration (Course 3037)45 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)46 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)47 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)48 Check the Routing (traceroute) (continued)

SUSE Linux Enterprise Server Administration (Course 3037)49 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)50 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)51 Analyze Network Traffic (tcpdump and ethereal) (continued)

SUSE Linux Enterprise Server Administration (Course 3037)52 Analyze Network Traffic (tcpdump and ethereal) (continued)

SUSE Linux Enterprise Server Administration (Course 3037)53 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)54 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)55 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)56 Determine the Status of All Network Connections (netstat) (continued)

SUSE Linux Enterprise Server Administration (Course 3037)57 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)58 Check for Service Availability (netcat) (continued)

SUSE Linux Enterprise Server Administration (Course 3037)59 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)60 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)61 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)62 Summary (continued) Command netcat –Used to test TCP and UDP connections Utilities tcpdump and ethereal –Used to capture and analyze network traffic