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10432
October 26th, 2017 12:00
What happens with IP address when computer goes to sleep?
We have many a Dell unit here that has the Intel I21* drivers (workstations) or 7260 drivers (laptops) and I'm wondering what happens with the IP address assigned via DHCP when the computer goes to sleep. Specifically, when the following setting is checked or unchecked for the NIC in the OS - "Allow the computer to turn off this device to save power".
We have been disabling "Allow this computer to turn off this device to save power" for quite some time, but I stumbled across this from the Intel Known Issues from the release notes regarding the I21* drivers:
Unexpected Connectivity Loss
----------------------------
If you uncheck the "Allow the computer to turn off this device to save
power" box on the Power Management tab and then put you system to sleep,
you may lose connectivity when you exit sleep. You must disable and enable
the NIC to resolve the issue. Installing Intel(R)PROSet for Windows Device
Manager will also resolve the issue.
We use the drivers from Dell and not the ProSet drivers. I'm going down this path because I'm in the middle of troubleshooting random "No logon servers available" messages when computers wake from sleep. I want to go ahead and enable the "Allow the computer" setting, but my manager thinks we turned this off to keep the machine from holding on to its DHCP IP when it goes to sleep - thus exhausting our IP lease pool. I don't remember it that way - I think if anything holds on to it it would be from ARP offload being turned on on the NIC, not this power management setting. We have very short lease times and this will not change due to our environment and the team in charge of the network. Anyone who can point me to detailed info on what happens with the IP address when the computer goes to sleep with and without this setting or can give a detailed explanation on this would be greatly appreciated.
robert p
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October 27th, 2017 05:00
Hi schappy26,
Thanks for posting.
Unfortunately, your question appears to be beyond the scope of this board, and you appear to be a corporate customer, so you might want to consult with your TAM as they will be familiar with your warranty.
Your company will have a Technical Account Manager assigned to assist with these types of issues. If you're unable to locate your TAM, reach out to your IT department or the Finance department.
Or maybe one of the Rockstars might know the answer.
schappy26
4 Posts
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October 31st, 2017 12:00
Thanks, Robert. I'm really just looking to find out if setting the "Allow the computer to turn off this device to save power" has anything to do with a workstation with a Dell NIC driver holding on to a DHCP IP address when the computer goes to sleep and then wakes up.
I did a test on my laptop and when I wake it up with the "Allow the computer..." enabled (before its lease time has expired) I immediately have an IP address and network connectivity. When I deselect "Allow the computer..." and wake the computer, there is a significant delay in getting a network connection (I'm assuming it is fully re-initializing the network adapter with this setting). If having the setting enabled doesn't attempt to "keep" the previously leased IP address and actually goes through the whole DCHP process to receive an IP, then I will turn the setting on in my environment to allow the NIC to be readily available upon returning from sleep.
eobiont2
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November 1st, 2017 09:00
I run into similar situations a bit. I think you are correct in guessing that ARP offload is what hangs on to the DHCP address. ARP Offload on intel NICs will even hang on to the IP after the DHCP lease is expired.
Computer turns on and receives a DHCP assigned IP with a lease of 4 hours (lets say)
If ARPOffload is enabled, the NIC will be set to respond to ARP requests on the network for that assigned IP.
Computer sleeps after 40 minutes.
After 3hours 20 minutes more, the computers lease expires and the DHCP address goes back in the pool.
A new computer comes on line and the DHCP server wants to reuse the expired IP address of the first computer. Before handing out that address to the second computer, it sends out an ARP request to make sure the IP address is free to use.
The NIC in the sleeping first computer with ARPOffload enabled incorrectly responds to the ARP request that it is still using the now-expired address.
DHCP receives the ARP ack from the first computer and marks the IP address as "bad" and takes the address out of the pool.
I have been dealing with this problem for years. There are some ways to work around the problem. Either disable ARPOffload (it is on by default in Intel Drivers), set the computer to wake up more frequently than the shortest DHCP lease time so the computer can renew its lease. Disabling ARPOffload will correct the problem - and so will allowing the computer to turn off the NIC when sleeping.
Note that if you disable the NIC, you will not have WOL ability. The computer doenst need an IP address to do wake on lan. As long as you are doing subnet broadcasts, the computer will still receive the magic packet broadcast from the switch even if its IP is expired. The OS will not respond to ARP when the computer is sleeping as long as NIC is not set with ARP offload enabled.
I am 87% sure of the information in this post. I wouldn't bet my life on it, but I'd wager a few donuts. I have run into this problem myself.