MAC Address / DHCP IP ¨Stealth¨ when I didn´t want it...

[IBMMuseum]

Maybe this will be better in ¨Rants¨...

Today I´m documenting all of the systems connected on the home network. An XP Pro system in a main room is notably absent in the list of DHCP clients on the router, even though it is on at the time. I check, and sure enough it is set to get the IP address via DHCP.

Next thought is that is an Intel NIC on an Intel brand motherboard, so maybe it has something to do with being a network ¨management¨ adapter. I install a SMC NIC in the PCI slot below it. Everything is identified, and I connect the cable to it instead.

No MAC address or IP shows up on the router...

I go through a few other cards, identifying a couple bad 3Com NICs, but it is the same at every turn with working NICs...

So I am frustrated, this is something to resolve another day. The original Intel NIC is put back in place, putting it in the next slot like the others I tried without success. It is redetected, and labelled as the ¨#2¨ in Device Manager.

And then I see I am out of ¨stealth¨ mode, the IP and MAC address are showing up on the router like they are supposed to...

I want that hour of my life back, upteen system reboots trying everything...

Never seen anything like it...

 

[barythrin]

Certainly a weird issue and no telling what it was at this point.. I hate those ridiculous troubleshooting sessions that don't make sense and fix themselves. If I had to guess it maybe was a dhcp lease time that XP may have gone past or failed to contact the router to renew it for some reason. From there sometimes XP will just accept that it was told to have this IP and it will keep it but periodically check for an authoritative response. That's kinda pushin it (thinking outside the box) but it could be the router had removed the lease from it's table and XP was happy assuming it had the lease until X time to retry (though an ipconfig /release and renew would have usually fixed that).. one would THINK a reboot or new NIC would also, especially with a different nic. I suppose a faulty network cable could maybe do something similar too (sporadic wire).

Very neat trick though ;-)

 

[IBMMuseum]

Certainly a weird issue and no telling what it was at this point.. I hate those ridiculous troubleshooting sessions that don't make sense and fix themselves. If I had to guess it maybe was a dhcp lease time that XP may have gone past or failed to contact the router to renew it for some reason. From there sometimes XP will just accept that it was told to have this IP and it will keep it but periodically check for an authoritative response. That's kinda pushin it (thinking outside the box) but it could be the router had removed the lease from it's table and XP was happy assuming it had the lease until X time to retry (though an ipconfig /release and renew would have usually fixed that).. one would THINK a reboot or new NIC would also, especially with a different nic. I suppose a faulty network cable could maybe do something similar too (sporadic wire).

Very neat trick though ;-)

It would be neat on occasion (say stealing Internet from a neighbor - I have a Linksys "gaming console" device that connects to an ethernet port to make it wireless, and it passes along the MAC address of the NIC - if I were driven to be such a low-life). But in this instance I wanted a visible IP (remoting in to the router, noting the IP, then setting up port forwarding for Remote Desktop). The same behavior despite changes in the NIC and drivers is what drives me crazy.

And then for the original NIC to suddenly shed the stealth once I put it back in place (thinking about it, I never remember an entry for the system on the DHCP table prior to this). I changed nothing in the XP configuration, nor knew enough to dog through the registry for such an obscure problem. Multiple reboots should have cleared the DHCP lease, and I saw no similar behavior for any of the dozen other devices I have on the network.

I work for an ISP, and I am intimately familiar with the functions of this router. In all the setups I've never had the issue before. It's fixed now, but I don't know the cause or the cure.

I never swapped the cable, but will check it for kid/pet abuse (another recent replacement elsewhere in the house had me wishing it would have given enough warning by taking one of nine lives) now that you mention it (connectivity was there the entire time - just that the IP didn't show on the DHCP table). A couple years back I kept a 5-port switch as a training aid to show a link light could be falsely lit (it was the switch, not any cabling). Reminding me, it came from the house, where I have good brand switches fail, but the no-name crap chugs on without issues.

Yes, I do my own cables, but I'm damn good at it, and aside from the mentioned cat-caused casualty above, have had no problems with it...

 

[glitch]

It's probably lease time as mentioned. I had that problem with a computer I used for college -- if you put it to sleep with one Ethernet connection active, then plugged into a different segment, it wouldn't request a new IP. If the Ethernet segment you moved it to was in a different address range, you lost connectivity and had to manually put the interface down and bring it back up. What's likely happened is that you got a lease, and then the router was restarted, and the Windows machine hadn't updated its lease since the restart.

This is another good reason to run your internal network with an authoritative DHCP server. That, and if your network is compromised, someone can enable their own authoritative server and Man-in-the-Middle everything going through the network without ARP poisoning or anything. We discovered this by accident, when someone plugged the LAN port of a Linksys router into the Ethernet jack in their dorm room, and gave new leases to most of the dorm I lived in.