MAC addresses started to get rejected
 

Hi all,

I hope this is a right place to post my question.

Last week, we had an outage in our company and lost network connectivity on some of the desktop machines and all of the laptop computers. We had to ask around and learn that if we change the NIC cards everything will work which turned out to be true. The laptops on the other hand, we couldn't fix yet.

We use ClearOS as our firewall but the DHCP server is on another machine and those laptops were all working just fine before this incident. Looks like these MAC addresses are somehow getting rejected but am not sure why. I checked the other server where the DHCP configuration is and everything looked fine. Please help me figuring out this issue.

Thank you in advance,
t

I'd think that changing more than one nic is a wrong cure. I can believe that one nic is a jabberer but not two or more.

I'd shut everything down. Switches and all computers before I'd change one nic.

Any place would be good to test. Ip or ipconfig command, arp, nslookup. Logging on to a switch or router for data. Wireshare.

Hi jefro,

Thanks for your reply. I found a file name dhcpd.lease, in this file the IPs we allocate to laptops are listed with expiration dates. Can I modify this file and chose never for end date?

There was a possible power outage, am not sure what exactly happened but on a Monday morning we came to work and one of the switches (the master switch) was down...Then we shut all the switches down and brought them up one by one and many of the desktop machines were back in business. About 12 of them were still having the limited or no network issue so we brought in a network engineer and the guy said the NIC should be replaced. We replaced the NIC cards ( meaning as you know new MAC addresses ) and everything magically started to work.

The laptop on the other hand still don't work. I connected one of my own laptops directly to the switch and it was working fine but the work laptop could not access the network when I plugged into the switch! The same faulty laptop works outside of the building...

Today, I found a dhcpd.lease file in which I see all the IP addresses we're supposed to be using for laptops and they all seem to be expired. Can I delete the file? The Monday which we came into the office and everything was down was on Sep. 26, 2011, note the date on one of the dhcpd.leases entries:

lease 192.168.1.22 {
starts 1 2011/09/26 20:51:51;
ends 1 2011/09/26 20:53:51;
tstp 1 2011/09/26 20:53:51;
binding state free;
hardware ethernet 00:08:74:b9:37:31;
uid "\001\000\010t\27171";


I think we're getting really close, I would appreciate it if you help me with this.

Thanks,
t

Usually dhcp is automatic. Just works fine. You may have somehow exhausted the lease pool. I think some log ought to show that.

You can set lease times. I the lease times are forever then all of the laptops should get the same ip. Normally ifconfig /release and a renew can fix it but a reboot should do that too. http://www.computerhope.com/issues/ch001078.htm for link to ways.

This still is not exactly what you are asking. Mac is not at the same layer. You diag mac by arp usually.

There are ways to diag dhcp also. You can wireshare it to view the entire sequence.

Are there any other devices that may have been set up to provide ip's?

You can use static arp to set in any ip to use as test or even use a static ip to diag it.