≡ Menu

dhcp client

I’m using FreeBSD 7.2 on HP laptop and getting IP info via WI-FI router. I’ve setup hostname in /etc/rc.conf buy after the boot process, I check host name with "hostname" command, but get empty line. Setting hostname with "hostname" works well, but after reboot host name is still empty. I suspect it has something to do with DHCP settings. How do I set hostname-using DHCP?
[click to continue…]

I'm using GNU/Linux with the Internet Systems Consortium DHCP Client. The dhclient, provides a means for configuring one or more network interfaces using the Dynamic Host Configuration Protocol. It also updates my /etc/resolv.conf file each time my laptop connects to different network. I would like to keep my existing nameservers. How do I skip /etc/resolv.conf update on a Linux based system?
[click to continue…]

Setting Up a CentOS / Red Hat Linux DHCP Client

Q. How do I setup my Red Hat / CentOS / Fedora Linux system to get IP address and other information via a DHCP server for eth0 interface?
[click to continue…]

How do I find out my DHCP server address?

Q. In Windows XP / 2000 / Vista ipconfig /all command will show me DNS server and DHCP server ip address. But, how to know DHCP server address in Linux?

A. The DHCP protocol allows a host to contact a central server which maintains a list of IP addresses which may be assigned on one or more subnets. A DHCP client may request an address from this pool, and then use it on a temporary basis for communication on network.

dhclient.leases file

Under Linux you use command dhclient to obtain and managing dhcp tasks. In order to keep track of leases across system reboots and server restarts, dhclient keeps a list of leases it has been assigned in the dhclient.leases file. On startup, after reading the dhclient.conf file, dhclient reads the dhclient.leases file to refresh its memory about what leases it has been assigned.

When a new lease is acquired, it is appended to the end of the dhclient.leases file. In order to prevent the file from becoming arbitrarily large, from time to time dhclient creates a new dhclient.leases file from its in-core lease database. The old version of the dhclient.leases file is retained under the name dhclient.leases~ until the next time dhclient rewrites the database.

Find out DHCP server address

Usually dhclient.leases file is located at /var/lib/dhcp3/dhclient.leases, type the following command:
less /var/lib/dhcp3/dhclient.leases
OR
cat /var/lib/dhcp3/dhclient.leases
Alternatively, you can just use grep command to get DHCP server address, enter:
grep dhcp-server-identifier /var/lib/dhcp3/dhclient.leases
Output:

lease {
  interface "ra0";
  fixed-address 192.168.1.106;
  option subnet-mask 255.255.255.0;
  option dhcp-lease-time 86400;
  option routers 192.168.1.1;
  option dhcp-message-type 5;
  option dhcp-server-identifier 192.168.1.1;
  option domain-name-servers 208.67.222.222,208.67.220.220;
  option dhcp-renewal-time 43200;
  option dhcp-rebinding-time 75600;
  option host-name "vivek-desktop";
  renew 0 2007/12/9 05:17:36;
  rebind 0 2007/12/9 15:06:37;
  expire 0 2007/12/9 18:06:37;
}
lease {
  interface "ra0";
  fixed-address 192.168.1.106;
  option subnet-mask 255.255.255.0;
  option routers 192.168.1.1;
  option dhcp-lease-time 86400;
  option dhcp-message-type 5;
  option domain-name-servers 208.67.222.222,208.67.220.220;
  option dhcp-server-identifier 192.168.1.1;
  option dhcp-renewal-time 43200;
  option dhcp-rebinding-time 75600;
  option host-name "vivek-desktop";
  renew 0 2007/12/9 06:11:22;
  rebind 0 2007/12/9 16:13:50;
  expire 0 2007/12/9 19:13:50;
}

A note about RHEL / CentOS / Fedora Linux user

Redhat and friends uses /var/lib/dhcp/dhclient.leases file:
less /var/lib/dhcp/dhclient.leases