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Chapter 2 Advancer Linux Netword Administration Network Troublesshooting of Lesson LPI 202 give you the knowledge: Common Network problems, hardware, Device Driver problems, IP Address,... With the specialized technology your information, this is a useful reference.
Chapter 02 Advanced Linux Network Administration Network Troubleshooting SaigonCTT All rights reserved Objectives • Be able to identify and correct common network setup issues • Have knowledge of locations for basic configuration files • Common tools and command are use to correct network problem LPI Linux Common network problems • Hardware • IP address • Routing and Ip forwarding • Hostname, DNS • Network services do not run • Firewall LPI Linux Hardware • NIC was not detected – Make sure your NIC has been attached correctly – Check system boot log: dmesg | grep eth – Check hardware compatible list – Check driver module or kernel • Network interface is not up – Wherether or not interrupt complicting – Check your cable – cat /proc/interrupts : check system interrupts – ifconfig a : view all interface has been detected LPI Linux Device Driver Problem • The system was not able to probe and identify network card – The network card is too old or is too new, – The card needs to be manually configured: ISA bus NE2000 cards, EtherExpress Pro's and the like • if you know the type of card, check and see the required driver: /lib/modules/kernelver/kernel/drivers/net Example: uses the 3c503.o module, attempt to load it with the command modprobe 3c503 – or need to pass some parameters for the driver. [root@baldur root]# modprobe eepro irq=5 io=0x300 • Once identified the correct driver module, can make it permanent: – /etc/modules.conf (2.4 ker) or/etc/modprobe.conf (2.6 kernel). – For example, the syntax to load the eepro.o: alias eth0 eepro options eepro irq=5 io=0x300 LPI Linux IP address • Ask network admin to find out your current subnet, default gateway, broadcast address, DNS server or using DHCP • Make sure ip complict do not occur • Check your ip address: ifconfig • Start, stop network service: /etc/init.d/network • Ping other host in the same subnet, or ping default gateway LPI Linux Interface Configuration • Use the ifconfig command to check to see that the machine's interfaces are up and have an IP address. [root@proserv root]# ifconfig eth0 Link encap:Ethernet HWaddr 00:08:A1:52:23:09 inet addr:10.11.2.1 Bcast:10.11.2.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:340802 errors:0 dropped:0 overruns:0 frame:0 TX packets:84583 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:22910593 (21.8 Mb) TX bytes:106456406 (101.5 Mb) Interrupt:22 Base address:0xd000 lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:7113 errors:0 dropped:0 overruns:0 frame:0 TX packets:7113 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:492201 (480.6 Kb) TX bytes:492201 (480.6 Kb) LPI Linux Interface configuration • Problems with an interface showing the wrong IP address, broadcast address or subnet mask are usually down to an incorrect entry in the configuration files – ifconfig eth0 192.168.0.1 netmask 255.255.252.0 – [root@sleipnir root]# cat /etc/sysconfig/networkscripts/ifcfgeth0 • Configuration by DHCP – If network interface is configured by a DHCP server, then the configuration script above will not specify the IP address: • ONBOOT=yes • DEVICE=eth0 • BOOTPROTO=dhcp • USERCTL=no – [root@sleipnir root]# dhclient eth0 LPI Linux Network Reachability • Once you've got an IP address on an interface, the next step is to test whether you can reach remote systems: – 1. ping the system's local interface • [root@sleipnir root]# ifconfig|grep inet inet addr:192.168.168.11 Bcast:192.168.168.255 Mask:255.255.255.0 inet addr:127.0.0.1 Mask:255.0.0.0 [root@sleipnir root]# ping c 2 192.168.168.11 – 2. ping the upstream router • [root@sleipnir root]# ping c 2 192.168.168.1 – 3. ping a remote host • [root@sleipnir root]# ping c 2 203.35.202.153 LPI Linux Routing and Ip forwarding • If you can ping machines on the local network but cannot get to all or some destinations on remote networks, then the problem could be in the routing table: – your machine – an upstream router • View routing table route netstat rn 10 LPI Linux Routing and Ip forwarding • Add new routing entry route add net network_addr netmask network_mask gw Gateway_addr • Add default gateway in other to connect to outside route add default gw gateway_addr • Ping remote host to check the connection • Use traceroute • Ip forwarding: /etc/sysctl.conf net.ipv4.ip_forward = 1 11 LPI Linux Hostname and DNS lookup • The problem is an inability to resolve names into IP addresses • /etc/resolv.conf nameserver 10.11.1.2 domain vnuitp.edu.vn • /etc/nsswitch.conf #hosts: db files nisplus nis dns hosts: files dns • Ping Ip_address to check the connection • Ping hostname to check DNS lookup – ping server.vnuitp.edu.vn – ping www.vnn.vn 12 LPI Linux Hostname and DNS lookup • Check whether your system is able to connect to a DNS and resolve a hostname into an IP address with the host command: [les@sleipnir les]$ host fulbertfulbert.cullen.lesbell.com.au has address 192.168.168.1 • To get down to lowlevel debugging of DNS lookups, should learn the nuances of the dig command [les@sleipnir les]$ dig www.pcuser.com.au @dvalin.lesbell.com.au ; DiG 9.2.1 www.pcuser.com.au @dvalin.lesbell.com.au ;; global options: printcmd ;; Got answer: ;; >>HEADER