Hi all,

We have DHCP server running on RHEL AS 4. Currently we are facing problem like, the DHCP scope gets full for one Subnet, but in practice when we scan for live IP addresses, there seems only about 70% IP addresses in use.

We have scope 10.8.117.41 - 10.8.117.254

We have looked in the dhcpd.leases file and we have observed that one single host occupies more than one IP addresses, which status is active for all IP addressess.

e.g.

lease 10.8.81.54 {
starts 4 2007/08/30 04:12:34;
ends 0 2007/09/02 04:12:34;
tstp 0 2007/09/02 04:12:34;
binding state active;
next binding state free;
hardware ethernet 00:50:8d:45:01:a1;
uid "\001\000P\215E\001\241";
client-hostname "computer1";
}

lease 10.8.81.219 {
starts 4 2007/08/30 04:16:26;
ends 0 2007/09/02 04:16:26;
tstp 0 2007/09/02 04:16:26;
binding state active;
next binding state free;
hardware ethernet 00:50:8d:45:01:a1;
uid "\001RAS \000P\215E\001\241\000\000\001\000\000\000";
client-hostname "computer1";
}


Above is an example of one host having Hardware address 00:50:8d:45:01:a1 registering more than one IP. There are many such examples of hosts having more than one IP active against their Mac address.

What I have observed that for every lease entry in a lease file, everytime there is a different uid. I really dont know what is uid, why is it changing everytime and how can I configure my server to ignore it and assign a single IP per MAC for any host?


Kindly help me...

you try to bound certain computers to a single ip by adding something like this to the conf file

or try to decrease the lease time.

I cannot bind IP addresses to MAC address for too many hosts and also there is no such need for it. And also even if I do lessen the lease period time, the problem still persists.

Kindly suggest what can I do so that my server will simply ignore the uid and assign one IP per MAC.

This can be due to :
1. if a client has been manually configured with an IP address which is managed by DHCP because the DHCP server usually attempts to verify whether an IP address is currently in use before assigning it to a client. However, there is no guarantee that the manually configured client is currently connected to the network or available to respond when the DHCP server is verifying the IP address. So, the DHCP server may assign the IP address to a DHCP client. When the manually configured client connects to the network, you will have duplicate IP addresses on your network. IP addresses that are managed by DHCP should not be used to manually configure the network setup for a client. If a client needs to be manually configured with an IP address, that IP address should be excluded from the DHCP server's address pool.
or
2. If multiple DHCP servers are configured to assign the same IP address if two DHCP servers are configured to assign the same IP address to clients, then it is possible for two different clients to receive the same IP address. One of the clients will receive the IP address from one of the DHCP servers, and another client will receive the same IP address from the other DHCP server. Multiple DHCP servers can serve the same subnet or network, but they should not be configured with the same address pool or overlapping address pools.

Thanks soroccoheaven for reply,

That may be the case, because there are too many users in our organization and we are not able to control the users from assigning Manual IP which is a part of DHCP Scope. And many a times we find such users who has assigned such Manual IP.

But apart from that, for my interest I would like to know,

1) why then the DHCP server keeps the Previously assigned IP active, if it fails to assign the previously register IP to a client ( Because of IP already exists somewhere else ), why doesnot it frees that IP when it assigns the new IP to the same client?

2) What is uid in dhcpd.leases file, and why is it different everytime for the same client (Especially when the same client has more than one IPs active against its MAC Address, which I mentioned in my previous post.) Can changing uid be a cause of DHCP server assigning different IP every time to the same host?

3) And are the MAC Binded IPs assigned to any other host to which it was not binded, in case of scarcity of IPs in the Scope.


Thanks in advance!!!

For questions 1,3 pls read the documentation so that you will get much more explanation.

Question 2.Actually the uid statement records the client identifier used by the client to acquire the lease but Clients are not required to send client identifiers, and this statement only appears if the client did in fact send one. Client identifiers are normally an ARP type (1 for ethernet) followed by the MAC address,like uid "\001\000P\215E\001\241" here 001 is for ethernet and remaining MAC.