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How do I configure fixed ip for a linux client on the dhcp server on 4506

I have successfully configured dhcp on a 4506.

It run good to the windows client.

But to the Linux client, clients couldn't receive the fixed ip.

I using the following config:

ip dhcp pool NetUnion202.115.22.129/26_FourT

host 202.x.x.134

client-identifier 0100.16d3.2b8c.2a

the MAC of client's pc is 0016.d32b.8c2a

When the client using windows, he receive the right ip address. But when he using the linux,

the receive a random ip 202.x.x.152.

show ip dhcp binding

202.x.x.134 0100.16d3.2b8c.2a Infinite Manual

202.x.x.152 0016.d32b.8c2a Aug 20 2005 08:47 AM Automatic

I had using client-identifier 0016.d32b.8c2a instead. But it didn't work.

show ip dhcp binding: 0016.d32b.8c2a Infinite Manual

202.x.x.152 0016.d32b.8c2a Aug 20 2005 08:47 AM Automatic

Anyone know the solution?



So, for this specific host, it receives a DHCP address OK from Windows, but it gets a different address under Linux (or no address at all)?

Do you have another DHCP server that does issue that address rnage?

DHCP will take an address from the first server that responds, if you have another server somewhere with that block, that is probably what's happening.

Check your first-hop/gateway settings for things like a DHCP Relay agent (Cisco = IP Helper) and verify that they are pointing to the correct zones.

Good Luck



I have confirm that there is no another dhcp server in this vlan and no ip helper address .

Any linux user will receive a random ip from the 4506 rather than the ip fixed on 4506.

for example, I using the config on 4506

ip dhcp pool FourT


client-identifier 0100.16d3.2b8c.2a

so the pc with MAC address 00-16-d3-2b-8c-2a

will receive the ip

In fact, it is right when he is using windows, but when he using linux on the same pc ,he would receive the ip

Any solution?



Did you try with prepending a 06 instead of 01?

As seen on this link

If that doesn't work you may need to "debug ip dhcp server packet" in order to see exactly which identity the Linux client is using.

You should see something like this:

DHCPD: DHCPREQUEST received from client 0100.16d3.2b8c.2a.

Or perhaps:

DHCPD: DHCPREQUEST received from client 0600.16d3.2b8c.2a.


Hi. What happens if you use the "hardware-address 0016.d32b.8c2a" command rather than the client-identifier command?

Dan :-)


I have use the if you use the "hardware-address 0016.d32b.8c2a" command , then when the client using the Windows XP , Vista and Slax(one publish version of linux ),it doesn't receive the fixed IP. While he using the Ubuntu, he reveive the fixed ip.

I have using the "debug ip dhcp server packets" command, I found that :

1. The former (XP Vista Slax) using the 01+MAC as their client-identifier.

2. The latter (Ubuntu) using the MAC as their client-identifier.

I will sniffer the DHCP packets on different platform. Any one can help me?



Find a true hub (not a switch) and place it between the host and the switch.

Also plug your analyzer in there (PC running WireShark, Sniffer, whatever) and set it capture

Power up the host while capturing.

You should see the initial broadcast (request) and then a series of unicast (host to server, then server to host), and probably a "gratuitous ARP" sent from the host to make sure the address is not already in-use.

If you can't find a hub, but you have a managed switch, most have some sort of "port mirroring" that allows you to copy all traffic to and / or from a switchport to a monitoring port (Cisco calls it "SPAN")

If you don't use a hub ow switchport that's mirrored, you will not see the unicast traffic between the server and host .... only the broadcasts.

You can download wireshark at, it's available in Linux and Windows versions.

Good Luck


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