Linux DHCP Network troubleshooting cases

One day a suse Linux 9.1 DHCP server was deployed on the network. DHCP is the Dynamic Host Configuration Protocol, which is used to automatically provide computers with IP addresses, subnet masks, and routing information. The software is simple to install on both the server and the client. But the clients on the network (using the operating system: Mandrake Linux 9.0, SuSE Linux 9.1) have no way to obtain an IP address. The experience may be that the Linux DHCP server is not able to receive request packets from the 255.255.255.255 DHCP client. Use the IFCONFIG-A command to query the server network card settings:

[Root@www cao]# Ifconfig

Eth0 Link encap:ethernet hwaddr 00:50:fc:56:75:f5

inet addr:192.168.1.4 bcast:192.168.1.255 mask:255.255.255.0

Up broadcast RUNNING mtu:1500 metric:1

RX packets:0 errors:0 dropped:0 overruns:0 frame:0

TX packets:4 errors:0 dropped:0 overruns:0 carrier:0

collisions:0 txqueuelen:100

RX bytes:0　(0.0 b) TX bytes:240 (240.0 b)

Interrupt:10 Base address:0x2000

......

Sure enough, there is no multicast set, why the system needs to have multicast function? The reason for this is that in order for DHCPD (the DHCP daemon) to communicate properly with the DHCP client, DHCPD must send packets to 255.255.255.255 this IP address, but in some Linux systems 255.255.255.255 this IP address is used as the IP address of the Listening zone subnet domain (local subnet) broadcast. So you need to add 255.255.255.255 to the routing table (routing table) to activate the multicast function; Use command: Route add-host 255.255.255.255 Dev eth0

The failure was eliminated.

If a 255.255.255.255:unknown host error message occurs, first modify the file:/etc/hosts and add a line:

255.255.255.255 DHCP

Save and then use the command:

Route add-host 255.255.255.255 Dev eth0

To save the settings, add a line to the file/etc/sysconfig/static-routes:

Eth0 host 255.255.255.255

The Routing table (routing table) is automatically set when the server is rebooted. The ifconfig query command is then used to check that the client using the SUSE Linux 9.1 system is working properly, and that the Mandrake Linux 9.0 client has not obtained an IP address. After referencing the Linux reference books and discussing with friends from the Linux community, the problem was found to be incompatible with the DHCP client program used by the Mandrake Linux 9.0 client and the DHCP server.

Troubleshooting method: Use the rpm command to uninstall the default DHCP client program used by Mandrake Linux 9.0 clients: dhclient; Install additional and DHCP server-compatible client programs: DHCPCD.

#/etc/rc.d/init.d/network Stop

#rpm-E Dhclient

#rpm-IVH dhcpcd-1.3.22pl4-2mdk.i586.rpm

#/etc/rc.d/init.d/network Start

Network and the new DHCP client to start again after a few seconds. Use the Ifconfig command to see that each Mandrake Linux 9.0 client has been assigned to an IP address. In the network for so each computer set IP address more cumbersome, using DHCP, these things are solved. The DHCP server can automatically assign IP addresses, but there are times when the server and the client are incompatible, and the client program must be replaced, and Linux provides four DHCP client programs: Pump, dhclient, dhcpxd, and DHCPCD. Understanding the client programs for different Linux distributions is important for Linux administrator work.