Today, I would like to monitor my internet network bandwidth. When my internet network is slow I often have questions from my boss “Why my internet network is slow, who are using a lot of internet bandwidth?”. I cannot answer these questions because I don’t have informations of current network status.

First step, I think I should know which IP Address is using a lot of internet bandwidth and second step I should know who is owner that IP Address.

The answer of the first step , I will use ntop software to answer this question. For the second step, I will fix all MAC Address of Laptop’s wireless card with IP Address on a DHCP Server. And this is my solutions :

1. Get a MAC Address from Client’s laptop such as  A1:B2:C3:A1:B2:C3

2. Add the MAC Address into the file /etc/dhcpd.conf such as

ddns-update-style interim
ignore client-updates

subnet netmask {

   # The range of IP addresses the server
   # will issue to DHCP enabled PC clients
   # booting up on the network


   # Set the amount of time in seconds that
   # a client may keep the IP address

   default-lease-time 86400;
   max-lease-time 86400;

   # Set the default gateway to be used by
   # the PC clients

   option routers;
   # Don't forward DHCP requests from this
   # NIC interface to any other NIC
   # interfaces

   option ip-forwarding off;

   # Set the broadcast address and subnet mask
   # to be used by the DHCP clients

   option broadcast-address;
   option subnet-mask;

   # Set the NTP server to be used by the
   # DHCP clients

   option ntp-servers;

   # Set the DNS server to be used by the
   # DHCP clients

   option domain-name-servers;

   # If you specify a WINS server for your Windows clients,
   # you need to include the following option in the dhcpd.conf file:

   option netbios-name-servers;

   # You can also assign specific IP addresses based on the clients'
   # ethernet MAC address as follows (Host's name is "laser-printer":

   host user-one {
      hardware ethernet A1:B2:C3:A1:B2:C3;
# List an unused interface here
subnet netmask {

3. Check your configuration file is correct :

# /usr/sbin/dhcpd -t -cf /etc/dhcpd.conf

4. Restart your DHCP Service :

# service dhcpd restart

5. Set DHCP relay in your CISCO switch points to your DHCP Server (Assume your IP Address of DHCP Server is

$ conf t
$ conf t > interface vlan 10
$ conf t > ip address
$ conf t > no ip directed-broadcast
$ conf t > ip helper-address
$ conf t > end

6. You can check all IP Addresses which receive from DHCP Server in file /var/lib/dhcp/dhcpd.leases
References :

How to fix MAC Address with IP Address on DHCP server.



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4 thoughts on “How to fix MAC Address with IP Address on DHCP server.

  • September 21, 2008 at 9:27 am


  • September 21, 2008 at 12:23 pm

    In the first time, all client’s laptop could not receive a IP Address because I didn’t set DHCP delay on my Switch.
    After I configured, all client’s laptop could receive a fix IP Address. 😀

  • September 30, 2008 at 3:56 pm

    hello P’aoddy

    It is a good idea for set subnet but it can give faster than your old net [before you are sitting the router] ??

    i will msn with you
    see you ^^

  • January 4, 2011 at 8:53 am

    One less pretty feature for me are the black borders around the screen. They are a bit too wide for my taste, it would’ve been better if Apple was able to stretch the display a little and remove the borders. On the top you get the sleep button that will deactivate the display. On the right side you get the volume buttons as well as the silence switch, interesting is that the buttons have been moved from left iPhone to the right. On the back you get the large black Apple logo in the middle of a big gray aluminum mass. It also says iPad on the back, the number of GBs and a few FCC things that are required to be there I think. It’s not impossible to assume that the new iPhone will feature a similar back. The tablet is really thin, in fact it’s just 0.5 inch thick, that’s as thick as an iPhone. Height and width measures come in at: 9.6 inches and 7.47 inch.

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