How to force +500 Clients to renew their IP address on the network ?

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nyckidryan@reddit

How much time do you have before the change needs to happen? 😉

If you have the time, change the lease time to 1 hour, then all the clients will request a lease renewal at 30 minutes. Make your changes, then after all the workstations have refreshed, change the lease time back to what it was.. or just leave it. 😄

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himji@reddit

Reboot the switches

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twisted-logic@reddit

Hi.. neteng here.. please don’t do this thing.

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HighRelevancy@reddit

I know enough about enterprise networking to know that there's much deep arcane knowledge I will never possess.

But that said, bruh, is your stuff really that fragile? Are you systems so delicate that a reboot scares you? Is there really such risk that it costs you more than a small amount of downtime?

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HoustonBOFH@reddit

To be fair... An 8 switch stack of 9300s can take 45 minutes to come back, so not a "small amount of downtime."

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HighRelevancy@reddit

Mama Mia. I've not dealt with switches like that. That does sound horrible.

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CrownstrikeIntern@reddit

First mistake, stacking them

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pdp10@reddit

This. If you're not confident that you can survive a simple power bounce, then tell me you're working right this minute on making sure you can survive a simple power bounce.

In a well-oiled computing infrastructure, you should be able to use your at-risk windows to randomly unplug some hardware or down some instances, chaos monkey style, and verify that everything stays up and/or recovers.

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twisted-logic@reddit

Not everyone works in a well oiled computing structure pdp10!!!!!

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Frothyleet@reddit

Yeah but there is a big middle ground between "my infrastructure is fully resilient" and "I lose sleep at night thinking about one of my switches rebooting".

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wrt-wtf-@reddit

Switches bouncing isn’t scary. It’s the ensuing argument that the switch has caused an issue when some of the systems connected don’t re-initiise as they should and inevitably it’ll be something politically sensitive that “the network broke”.

This is something you’d normally see in a data centre environment and the devices would normally be fixed IP anyway. I’ve seen mainframe-FEP drop their interface and stay down with a similar scenario on Linux deployments that aren’t properly configured.

I love explaining network issues to sysadmins in-depth so that they can learn - but there should be some different risk mitigations about a DC reboot vs an edge switch that manages end user devices rebooting.

IOT devices, printers, access points, and currently connected devices.

As an absolute minimum, you let all stakeholders known what you are going to do, snapshot the switch state, including Mac-address table and port mapping, write the config (Cisco), restart the system. Snapshot the state after reboot compare everything and let stakeholders know that certain devices disappeared - or you fixed them yourself.

But these “network issues” aren’t a network issue - they’ll inevitably be reported as a network issue and administering managers will blame the outage on the network when it is the connected device that has failed to do the required interface re-initialisation.

It’s the layer8 issues that lead to network engineers being concerned about switch reboots. Not the fragility of the network devices and configs. It’s the network engineer that takes the hit for poorly configured systems.

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twisted-logic@reddit

Yeah.. evidently hyperbole is not defined in this subreddit. It’s just a joke lol

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Frothyleet@reddit

It's more that there is a substantial contingent of people who have real crappy environments and rather than improve things they roll their eyes and say "ugh god all these high falutin' enterprise sysadmins don't understand how things are in the REAL WORLD".

And so you just never know if someone is being jokey or incompetent ¯\(ツ)/¯

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twisted-logic@reddit

Fair enough. I’m not on here much so I didn’t realise that lol.

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root-node@reddit

Everyone has a test environment, some people also have a production environment

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Tetha@reddit

Something I also push: There is a difference between respect and fear.

I am confident that if I trigger a failover on any of our PostgreSQL clusters even during peak load, it will be 1-2 seconds of outage, a bunch of cancelled requests and bounce right back. We've tested this under load during announced chaos tests and various production incidents of database abuse :)

Quite a few of our upgrade procedures are built upon the idea and confidence that we can failover and reboot unattended and it will go right. Or if a security or larger availability concern hits us, I'm entirely willing to push that button whenever.

I however also know how this can cause a bunch of support tickets when done during peak load, so I'd prefer to do this outside of peak hours, usually in the late afternoon, to the more critical systems.

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hornethacker97@reddit

My knee jerk reaction is that someone outside of networking may not know the condition of the config backups 😆 or what level of work it might take to physically terminal into switches if they don’t come back up correctly

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abakedapplepie@reddit

better to find out you fucked up that bad during a planned outage than an unplanned one

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Cormacolinde@reddit

I’m sorry, but if your config is not properly saved and backed up, you have a serious issue that a simple power flicker would trigger. That’s BAD.

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twisted-logic@reddit

It was more just a joke tbh.

As with everything in life though, it depends. If leadership hasn’t shelled out any cash for infra replacements in long while then yes. Yes I am afraid to reboot that Cisco 3850/3650 that’s been up for over 3 years. No I do not want to touch that catalyst 4500. Those things scare me.

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Downinahole94@reddit

Jesus, that's the stuff I use in my home lab, because it's old and cheap.

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benderunit9000@reddit

The configuration should not be that fragile.

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RelevantToMyInterest@reddit

former neteng here...

DO IT YOU COWARD!

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Dorest0rm@reddit

Yolo

Okay, why not?

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Cyber_Faustao@reddit

If your infrastructe can't survive a reboot then it is already broken and just awaiting for a trigger for it (UPS fault, intern pulling the wrong cables, etc).

So perhaps its time to fix that?

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HoustonBOFH@reddit

Also net eng here... And often a properly cascaded reboot of the switches can solve a lot of problems.

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JoeyJoeC@reddit

Why not? Worked when I needed to do it.

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fragwhistle@reddit

If you want to be a bit more graceful, do a shutdown on all of the access ports and the no shutdown. If you want to make sure they all come up with "new" addresses, delete the leases between shutdown and no shutdown.

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MarzMan@reddit

Ricoh Printer: Oh, the nic went down? Guess I have the rest of eternity off.

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thelordfolken81@reddit

Please save the config first …

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ansibleloop@reddit

I have all of mine in Ansible

Reload away

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benderunit9000@reddit

IaC or bust

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gnartato@reddit

Cisco boiii confirmed.

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Head-Web-404@reddit (OP)

Sometime, there are switches behind switches, which will not have impact on endpoints

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gnartato@reddit

Have you considered flipping the circuit breakers for the entire building? It will leave the switches up (if UPS protected) and reboot all the clients. If you're worried about wireless clients just reboot all the APs at the same time

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Brraaap@reddit

ALL the switches

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Proof-Variation7005@reddit

Do the light switches too.

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DontDoIt2121@reddit

Kill em all!

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Evil-Bosse@reddit

Instructions unclear, found a big switch in electrical room, even the servers rebooted from that one

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Brraaap@reddit

That'll do it

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himji@reddit

Yes all

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Tasty_Switch_4920@reddit

Processing img z2bfhkticstg1...

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Pleased_to_meet_u@reddit

If you haven't read the original comic, it's a LOT of fun.

Hyperbole And A Half: https://hyperboleandahalf.blogspot.com/2010/06/this-is-why-ill-never-be-adult.html

u/GullibleCrazy 488, you'll like this.

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GullibleCrazy488@reddit

too funny!

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Pr0fessionalAgitator@reddit

gif

Every switch?

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MetaVulture@reddit

Power cycle the facility itself.

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MiXeD-ArTs@reddit

This was my first thought.

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anxiousvater@reddit

That's what I did at home, a short circuit to replace a bulb forced many devices to get a new IP address.

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ExpensivePoint3972@reddit

bomb the power plant

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oliland1@reddit

Cut power to the building until all UPS run out

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kristianroberts@reddit

Wouldn’t necessarily work. Clients are selfish and can just skip discover/offer and go straight for a request if they detect it’s a known network. Heck, some clients (Apple) try override the lease times.

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CyberRedhead27@reddit

Just "shut" - "no shut" the ports.

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dont_ama_73@reddit

Run Cisco switches, wait for a unexpected crash. Wont take long

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bgr2258@reddit

Change DHCP lease time to 30 minutes. Wait at least as long as the old lease time for everything to expire

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BigChubs1@reddit

This. And I’m curious why op wants and/or why has to do this

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The-Sys-Admin@reddit

Printer has a static IP and they can't get to the client that was assigned the same Ip.

Tsk tsk... No DHCP reservation.....

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Cloudraa@reddit

So just turn off the printer and run /renew on the client then add a dhcp reservation hahaha

or even better don't put static network device IPs in your dhcp scope!! gahh

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Fraktyl@reddit

I inherited my network. The number of hard coded IP's in the DHCP scope was staggering. Almost got it where it needs to be, but man was that a mind blowing experience when I opened the DHCP manager.

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Master4733@reddit

My inherited network was like that.

But they weren't reserved in the dhcp scope, they were just assigned and at some point other devices managed to get the IP address.

I had half a dozen switches and ap's just sitting there with power and no network connection

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mountain_bound@reddit

My inherited network is dishing out dhcp from a hand full of Sonicwall firewalls and there's no server system anywhere. The thought of lifting this site into something useful is exhausting.

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Fraktyl@reddit

That's exactly what happened here. Random printers just stopping as new computers came online.

I've got the hardcoded ones reserved and remove the reservation as I get them out of the scope. Making a management VLAN really helped clean up the IP address space.

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TU4AR@reddit

I once walked into a client that the first 5 ips of every network was SOLELY And ONLY for network printers.

Example :

172.0.0.1-5 will be for the office. Got a 6th printer?

172.0.1.1-5 will be used for the next five Printers.

172.0.2.1-5 will be used for the third batch. So on and so fourth.

So if you think your Networking is bad, just remember some guy got paid more than you to make these decisions.

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SinTheRellah@reddit

Could be a lot worse tbh.

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TU4AR@reddit

Always is, doesn't hold a match to a guy naming servers after moons of Jupiter.

Who the fuck knows what Callisto does.

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FarmboyJustice@reddit

This is not that bad, at least the printers aren't restricted to prime number octets.

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sir_mrej@reddit

I mean this just sounds very late 90s/early 2000s. It was prolly an old guy who was doing what he had always done.

That's not the worst thing I've ever seen

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Nydus87@reddit

I can at least sort of see the logic there, but it doesn't scale well if you've got a printer heavy office.

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maxtimbo@reddit

or even better don't put static network device IPs in your dhcp scope!! gahh

It's really that easy.

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MrChach@reddit

I can’t tell you how many idiot “IT Guys” don’t understand how much time and effort DHCP reservation save. “The vendor says make it static”. “Let’s keep it DHCP with a reservation. It’s easier to manage. “, “The vendor says they won’t support that. “.

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The-Sys-Admin@reddit

Do it have a MAC address? Then the vendor don't need to support shit!

It's frustrating to inherit a network like that. Just left my last place with that mess.

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UntouchedWagons@reddit

Who's the dude in your avatar?

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The-Sys-Admin@reddit

Kenan Thompson, most recently of SNL fame.

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Gadgetman_1@reddit

If that was the issue, they could find the Switchport of the offending machine, and just disable it.

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jbp216@reddit

change the printer ip. are you not connecting via dns?

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hihcadore@reddit

Guessing this is an onion of bad

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The-Sys-Admin@reddit

This is healthcare mother f****r. Printers were installed before the domain. IP access only.

We ain't got time to update DNS records or DHCP scopes.

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someguy7710@reddit

I've had to re-ip a whole network before. Why? Because they were using a public ip block the they no longer owned for their lan. I don't know why!

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GullibleDetective@reddit

Ip change project

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Belchat@reddit

Moving clients to a new range perhaps

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Dabnician@reddit

they might have changed the dhcp options

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Fallingdamage@reddit

Or reboot the core switches.

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wrt-wtf-@reddit

Won’t do anything. You need to cycle the interface that the devices are connected to.

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tdhuck@reddit

Yup, this is what I do when I anticipate making changes, this of course assumes I have time to do this. My lease times are set to 24 hours.

If I have to make a change immediately (can't recall any time that this had to happen immediately). I'll make the DHCP changes needed, set the lease time to something low like 15 minutes, just in case I need to make another quick change, then I start deleting leases. While it might not work for online hosts, it does seem to work for offline hosts that are holding on to an IP that I don't want to be available for the next 24 hours. If the client is active on the network, I'll ask HD to get with the user and see when they can reboot the PC.

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ranger_dood@reddit

If a client thinks its lease is good for 7 days, wouldn't it not check in at all for at least 3.5 days (assuming no reboots or network status change).

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when_nerds_cry@reddit

Half as long, initial lease renewal attempt on dhcp is at the halfway point, anything online at that time will renew their lease, anything offline will just do it when they come back online, this is a safe method

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Frothyleet@reddit

That behavior is true for the Windows DHCP client, I don't know if it's universal.

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when_nerds_cry@reddit

Well it should be as this behavior for T1 is defined in RFC2131 the actual DHCP spec, so unless your client doesn't follow the actual DHCP specification you are pretty safe

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Gadgetman_1@reddit

Older Cisco Videoconferencing units?

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when_nerds_cry@reddit

Do older cisco videoconferencing units not follow the RFC spec for DHCP? idk the answer to that - most of our cisco gear responds as expected, I typically do this same process on my voice vlan's whenever we change scope or options and they always pick up the change at the half way mark as expected

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Gadgetman_1@reddit

We had one that didn't behave, at least. It has long since been recycled, though, so it can no longer hurt any networks.

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HappyVlane@reddit

It's true for everything that follows the RFC default values.

Times T1 and T2 are configurable by the server through options. T1 defaults to (0.5 * duration_of_lease). T2 defaults to (0.875 * duration_of_lease).

https://datatracker.ietf.org/doc/html/rfc2131#section-4.4

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Frothyleet@reddit

Thank you, I couldn't find it when I skimmed the RFC a while back so I didn't know if it was actually prescribed behavior or just common practice.

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nof@reddit

Renews start after 50% lease time. Should save a few hours/days/weeks depending on how insane the old policy was.

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thepfy1@reddit

Set it to 1 second

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bwalz87@reddit

I was thinking the same thing

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apb91781@reddit

Change the base IP. Instead of 198.0.. * to something like 198.1.. *

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nyckidryan@reddit

That won't force a renewal until 50% of the DHCP lease time has expired.

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wrt-wtf-@reddit

If you’re desperate and don’t mind taking the hit, cycle the switch ports with a script or reboot the switches.

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Pristine_Curve@reddit

If it is a planned change, reduce DHCP lease time ahead of the change.

If it is an unplanned change where you can't prepare in advance, restart the access layer switches.

Last resort, tell everyone to restart.

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SirLoremIpsum@reddit

Last resort, tell everyone to restart.

SECOND last resort

Last Resort is flipping the breakers to the building :)

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engy1207@reddit

ah yes, the classic "the fastest way to shut down all the computers in a room is a short-circuit connector in the nearest outlet"...

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Xoron101@reddit

Last Resort is flipping the breakers to the building :)

Well shit, since covid everyone now has a laptop. So this won't work for us.

How about a solar flare?

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engy1207@reddit

reboot every access point. Preferably at the same time. When they reconnect they should get a new address (you don't have static Wifi addresses, do you?
Alternatively rename every SSID...

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vppencilsharpening@reddit

Dude the last time we did this the electrician didn't want to touch it with a 10ft poll and I don't either.

It was turned off on a weekend planned well in advance. The electrician turning the breaker back on had to crank a handle a few times and then push a button to "flip" it back on.

He pushed the button with two wooden broom sticks taped together while looking the other way after clearing everyone from the room.

Apparently if it failed to turn back on the electric company was on 12-hour standby to cut the power at the pole so the breaker could be safely replaced.

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patmorgan235@reddit

Ooh yeah, Google "arc flash" for what the guy was scared of

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Azuras33@reddit

And tell it's the electrical compagny fault.

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Pork_Bastard@reddit

i always love bouncing the switches for this task!

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lazyhustlermusic@reddit

Describe the silly thing you did to put yourself in this situation

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some_string_@reddit

Haha, YES!

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Silver-Preparation20@reddit

Reboot your switches.

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Evening_Plan_2302@reddit

ipconfig release && ipconfig renew

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guitpick@reddit

We can't emphasize enough how important the && is if you're running this remotely or from a batch file on a network share. Splitting this into two lines disconnects before getting the renew.

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wezu123@reddit

Nostalgia throwback to myself trying to restart the NIC, and getting myself locked out

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SirLoremIpsum@reddit

I always knew there was a better way to do it but I never could be bothered to work out how...

I will file this away!

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guitpick@reddit

Honestly, using a single & might be better in this case, as && only runs the second part if the first one succeeds. If the /release errors out for some reason, you still might end up disconnected.

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WhenTheDevilCome@reddit

Roses are red
Violets are blue
This line releases,
...

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jeffrey_f@reddit

Rambo? Afterhours, drop the breakers and bring each area up a few seconds apart, except the data closet.

The nicer way? Drop the switches for about 30 seconds and bring them back up.

Likely the right way is to tell everyone to shut the computers off before they leave, but they won't all comply so dropping the switches for about 30 seconds and back on.

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Talino@reddit

I’ve done this to switch subnet before. Created a new VLAN in the network core with its own DHCP and then for each endpoint switch, made the new VLAN untagged on the trunk from the core and rebooted the switch.

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Hot-Comfort8839@reddit

$hosts = @("host1", "host2", "host3")

Invoke-Command -ComputerName $hosts -ScriptBlock { ipconfig /release; ipconfig /renew }

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darthfiber@reddit

Why don’t you start with what you are trying to accomplish and your environment? If you are trying to change the IP scope for example you could configure a second address if your gateway supports it and configure a new scope.

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tomasalves35@reddit

This

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flaccidplumbus@reddit

Power cycle switches

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flaccidplumbus@reddit

Flip a breaker

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cbowers@reddit

Do you not have an agent installed that you can run a local command shell command with? For us, we could send an “ipconfig /release && ipconfig /renew” via an OS task in the ESET server console to all servers and endpoints; or send it via the ScreenConnect or Connectwise Automate console, or even the managed Velociraptor agent from the Rapid7 SIEM agent.

We completely re-segregated the network into additional subnets and VLANs with most endpoints not even noticing the 1 second blip.

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Kapzlock@reddit

Reboot the switches 😈

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russellbarrick@reddit

I have seen far too many answers before I got to the first person saying reboot the switch. This is the way and I will also add to blame a rogue emf storm if anyone notices.

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Latter-Ad7199@reddit

You could fuck about trying to script remote commands or some shit

Or

Just reboot the access switches

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orion3311@reddit

Power cycle the switches

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landob@reddit

Last time i needed to do this i just powercycled the switches. Not fancy, but it worked

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TrippTrappTrinn@reddit

New DHCP scope. Delete the old scope and let nature do the rest.

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Head-Web-404@reddit (OP)

Computers will wait till the lease expires before trying to contact DHCP SERVER.

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FrankNicklin@reddit

No, renegotiation starts at 50% of the lease time. a T1 request is sent at 50% lease time then the next T2 at 87.5% of the lease time, if that fails then at 100% the device in theory looses the IP address.

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dnuohxof-2@reddit

I never knew this about DHCP. Neat

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uptimefordays@reddit

Yep DHCP leases use a half life!

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ErrorID10T@reddit

In theory. There's always that one device where the manufacturer decided to put their own specification in for when and how it should renew, because not following standards is how you know you have a quality product.

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ErrorID10T@reddit

Plan ahead, set your DHCP lease time really low, and then update the DHCP scope, options, or whatever. Alternatively if you have some sort of tool that can push out scripts or commands just manually run a command to do it.

DHCP renewal is initiated by the device, you have to instruct it when to renew either by manually renewing or giving it a specific lease time.

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simonjakeevan@reddit

Wouldn't Ipconfig /release /renew work?

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ErrorID10T@reddit

That's a horrible idea. You don't need the /release, you can just do /renew. /release, if anything goes wrong with the renewal process, can result in a whole bunch of computers offline that need to be manually fixed or rebooted to come back online.

Just ipconfig /renew is a better solution.

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DekuTreeFallen@reddit

It is a bold strategy to ask for help with DHCP, and then to spend one of the few replies incorrectly trying to correct someone else on DHCP. Do you want the help or not?

I'm kidding, I know you didn't mean anything by it. It is still funny though because a few people in this thread have asked for more information about this x/y problem, and instead of replying to them, you spend the time with the above reply.

Question - did you manually configure these computers to be out of compliance with RFC 2131? Are these computers typical workstations or something else?

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Head-Web-404@reddit (OP)

I gave more information under some comments here. Clients are workstations running windows 11.

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techforallseasons@reddit

Typical is ~50% of lease time to "renew"; but they are not REQUIRED to follow that pattern.

Printers for example...

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raip@reddit

Technically - it is part of the specification (RFC 2131) so they are required to do so. Whether or not they actually do is a completely separate question.

Zebra printers, for example. are a fucking nightmare. They don't even adhere to the appropriate DORA specification when you invalidate their lease, they'll just hold onto the existing one until you actually kill their network connection (and those wireless ones will keep their IP address even when they hit their lease expiration completely).

It's a large reason why in my previous org that we continued to setup static IPs for the Zebra printers even after all other devices were converted to DHCP + Reservations.

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techforallseasons@reddit

Yeah -- cameras and HVAC controller can be similar. We set them up static and set a reservation in DHCP for record-keeping.

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LUHG_HANI@reddit

Zebra industrial label printer reverting to DHCP is the stuff of nightmares.

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rubmahbelly@reddit

If you need it pronto maybe write three lines in Powershell/CMD and push it via software deployment? Inform users upfront?

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DULUXR1R2L1L2@reddit

So (in advance) set the lease time to a low number so they naturally expire, make your changes, test, change the lease time back.

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raip@reddit

Clients actually contact the DHCP server at 50% to renew (or at 87.5% if T1 fails). If the lease is no longer valid (DHCP NACK), a good client would go through the DORA process again.

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TrippTrappTrinn@reddit

Yes, that is the natural way. If you have client management, just push out ipconfig/renew.

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Sobatjka@reddit

Yes.

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curi0us_carniv0re@reddit

Unplug the switches 😅

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twolfhawk@reddit

Expire all lease. Fortinet, unifi, watchguard, Cisco they all have a method

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Head-Web-404@reddit (OP)

To force a client to expire his lease ? How

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twolfhawk@reddit

Depends on the system. In watchgueard system manager its literally right click the firewall and "expire lease"

For others its cli

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Whole-Ad-3196@reddit

https://www.reddit.com/r/WatchGuard/comments/18jsy12/expire_lease_tool/

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twolfhawk@reddit

So watchguard lied to me...

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Whole-Ad-3196@reddit

Love how there is always someone who thinks there's some magical purge button on the Firewall/DHCP server that will do this without having to do anything on the client or caring about how DHCP actually works.

I.E Watchguard does not have a method; you can reboot, which can clear the lease pool, but the hosts still technically own the IP address they were originally assigned based on whatever the original lease was, or 50% whatever.

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twolfhawk@reddit

Guess you never used cli. You are technically correct, lowering lease time will work when the existing lease ends. However, when you need to nuke it, you nuke it.

If you want to trigger all Windows devices- use powershell.

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newtekie1@reddit

Have you tried turning the entire network off and back on again?

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Spiritual-Yam-1410@reddit

Reset the DHCP scope? That'll force renew on next check-in. Or just reboot the switch they're on if you want chaos. What's the actual problem you're solving?

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chasingpackets@reddit

Have a planned unplanned power outage in your MDF/IDFs and boot your access layer infrastructure.

It will all work itself out.

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Weary_Patience_7778@reddit

Power cycle your switches :)

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Ok-Butterscotch-4858@reddit

Just f it and reboot it 😂

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thaneliness@reddit

Do you have said clients on an RMM? I personally would just execute a script. Here’s simple one for powershell:

ipconfig /release ipconfig /renew

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howboutno55@reddit

Just make sure it's one script lol, I immediately imagined a case where some bonehead messes up and sends out release and renew as two separate scripts, the workstations process the release command and are no longer on the network to receive the renew command.

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thaneliness@reddit

😂😂

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Serapus@reddit

If only for security, printers should be on their own VLAN(s) and static if possible. Segment your network, but don't go bananas.

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kooroo@reddit

power cycle the building.

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LokiLong1973@reddit

Better even, power cycle the universe, just to be sure.

[-]

enigmaunbound@reddit

Throw a squirrel at the local power substation?

[-]

AlkalineGallery@reddit

This is the only correct answer in the entire thread.

[-]

FarmboyJustice@reddit

If the goal is just to get all clients to renew their existing leases, power cycle the switches.

If the goal is to force all clients to get new leases with new parameters, delete all the existing leases, then power cycle the switches.

[-]

NorthAntarcticSysadm@reddit

Restart the client access portion of the network stack

Or, plan well in advance and shrink DHCP lease

[-]

buck-futter@reddit

Send the command:

ipconfig /release && ipconfig /renew

I've noticed Windows clients sometimes don't fetch a new list of DNS servers when renewing the lease unless it was released first. So if you're changing your domain controller IP address and they're also the only DNS servers, you'll need to do this command or reboot every workstation.

[-]

Ok_Perception_294@reddit

Reboot the core switch during prod, issue resolved.

[-]

jdiscount@reddit

Not enough information

What type of clients?

Windows, Linux, MacOS, BSD, Solaris etc.

How do you manage them, what's your DHCP server.

Have you tried anything before making a low effort reddit post?

[-]

Head-Web-404@reddit (OP)

All windows and DHCP server is on The Firewall

[-]

jclimb94@reddit

Have you tried forcing an unexpected reboot?!?

[-]

Head-Web-404@reddit (OP)

Like I said before, this will required rebooting all the switches across the building, and some tiny switches are unmanaged so you have to well know the building and where every single switch is located

[-]

Wolfram_And_Hart@reddit

Active Directory?

Import-Module ActiveDirectory

$OU = "OU=Workstations,OU=Computers,DC=domain,DC=local" $Computers = Get-ADComputer -Filter * -SearchBase $OU | Select-Object -ExpandProperty Name

foreach ($Computer in $Computers) {

Write-Host "Processing $Computer..." -ForegroundColor Yellow

if (Test-Connection -ComputerName $Computer -Count 1 -Quiet) {
    try {
        Invoke-Command -ComputerName $Computer -ScriptBlock {
            ipconfig /release
            ipconfig /renew
        }
        Write-Host "DHCP reset successful on $Computer" -ForegroundColor Green
    }
    catch {
        Write-Host "Failed to run command on $Computer" -ForegroundColor Red
    }
}
else {
    Write-Host "$Computer is offline" -ForegroundColor DarkGray
}

}

[-]

StrikingPeace@reddit

change the DHCP and force reboot the clients

[-]

dathar@reddit

Have a live demo of the building's diesel generator switchover.

[-]

atw527@reddit

Cycle power to the building.

[-]

ferrybig@reddit

For modern IP, just push an IPv6 ICMP router advertisement with the old prefix set to a lifetime on 0 seconds and the new prefix they have to use with a lifetime in the future

[-]

Intrepid00@reddit

Power cycle all the switches

gif

[-]

Foxk@reddit

Goverlan!

[-]

PH_PIT@reddit

ipconfig /release && ipconfig /renew - in the login script?

[-]

systonia_@reddit

set low dhcp lease time

remote powershell to ipconfig /renew

GPO with a runonce scheduled task to ipconfig /renew

turn switchports off/on

reboot clients

reboot switches

Powercycle entire building

[-]

ccsrpsw@reddit

If you are moving machines to a new subnet rather than just renewing their addresses, dropping the network on the switch side is the only way to force it (shut/no shut on the port) realistically. (Just been through this with a re-iping of a whole site).

If you just want to refresh the pool and can reach the machine then a:

$complist = { "comp1", "comp2", ... , "compN" }
foreach ($c in $computerlist)
{
    Invoke-Command -ComputerName $c-ScriptBlock {
        ipconfig /release
        ipconfig /renew
        }
}

Is probably your only other alternative (theres probably a typo in there since I just thew it together in the Reddit editor not VSCode

[-]

Omadon667@reddit

I think this is the best answer, as its the one I always used to use. 😃

[-]

SylvainLafrance@reddit

By far the most interesting solution 👍

[-]

ParticularDonut7555@reddit

Go to your DHCP console, select the scope, and delete the current leases. What happens: The next time a client talks to the network (or when their half-lease time hits), the server will tell them their old IP is gone and force a new DORA process

[-]

unnecessary-ambition@reddit

And when the new lease issues an address that a different client is still using because it's not at its half-lease time yet, that's when the real fun begins.

[-]

kribg@reddit

This seems like a great way to get duplicate IP addresses assigned. Since the dhcp server no longer has a history of what was assigned and some machines will still have the old address for a while you can get overlap.

[-]

Sgt_Blutwurst@reddit

[-]

Millzee69@reddit

Why?, first question i’d ask then plan accordingly. Are clients over vpn, local etc… can gateway be changed temporarily to force new addresses. Id set whats existing lease time. New network/vlan etc?

The main question still stands - why?

[-]

ultradip@reddit

Set the DHCP expiration to 1 hour?

[-]

pdp10@reddit

One does not simply force DHCP and WiFi clients into anything. You have to make them want to do it.

Depending on what you're trying to solve, you could send IPv6 Router Advertisements and give everything a new or additional IPv6 address in 5 to 10 seconds, though.

[-]

hornethacker97@reddit

I just want to know why a medium size business’ LAN doesn’t have IP scavenging enabled in DNS 🤦‍♂️

[-]

rswwalker@reddit

So many people suggesting rebooting switches don’t seem to realize how disruptive that is! Most enterprise switches take time to restart and if they are stacked it could take even more time. There are also WiFi APs getting PoE from those switches which will also reboot.

Do not reboot switches.

You can either, a) wait for clients to auto renew, and reduce lease time for the future it its too long, or b) push an Intune script or GPO immediate task to do an ipconfig /renew. You don’t need an ipconfig /release if you’re not changing IP subnets and is also disruptive, might as well ask users to reboot.

[-]

Grand_rooster@reddit

If windows machines then run a script on a loop.

Ipconfig /renew

I use sysquerypro to help multitask.

[-]

Need_no_Reddit_name@reddit

If you know the names of the devices, and you have Remote management set up correctly, a script (or scripts) will do the trick.

For example if they are windows devices and you have WinRM and psremoting enabled (and the correct permissions setup). Then you could pull the list of computers from AD and have the script run through the list using invoke-command to run ipconfig /renew.

If that will not work, then do as others have suggested and change your dhcp lease time

[-]

mymonstroddity@reddit

If they are managed, deploy a task to execute command ipconfig /release && ipconfig /renew

easy peezy

[-]

mymonstroddity@reddit

But also remember to clear the dhcp reservations first

[-]

redtollman@reddit

In a past life I’d: psexec /s @hosts.txt ipconfig /renew

[-]

ender-_@reddit

psexec -h -u YOURDOMAIN\administrator \\* ipconfig /renew

^(don't do this)

[-]

thomasmitschke@reddit

Disconnect them from the switches-port disable and then enable. 2 commands per stack.

[-]

djmonsta@reddit

Disable DHCP scope. Wait 10 mins. Reenable DHCP scope.

/s

(Seriously, don't do this).

[-]

antomaa12@reddit

If you can, you could do it with PSExec, or if you can get a CSV with all computers names / IPs, you could create a small PowerShell script which do a ForEach and executes the dhcp force renew command via PS-Sessions

[-]

no_your_other_right@reddit

If they are all or mostly Windows endpoints, use Powershell.

Invoke-CimMethod -ComputerName "RemotePCName" -Namespace "root\cimv2" -ClassName "Win32_NetworkAdapterConfiguration" -MethodName "RenewDHCPLeaseAll" ```

[-]

Creative_Progress803@reddit

If the addresses are from a DHCP lease, I'd set the lease time to 10 minutes, go get a coffee and set the lease back to whatever value it was prior my changing.

[-]

samueldawg@reddit

Script to bounce all switch ports on all switches - except trunks

[-]

admlshake@reddit

Step 1. Find the breaker panel...

[-]

Master-IT-All@reddit

I issue a command in RMM.

[-]

guitpick@reddit

If these are Windows machines, psexec or schedule a one-time task in group policy to do an ipconfig /renew. A `FOR /L` loop in an interactive command prompt running as admin can knock out a bunch at once for an IP range.

for /L %C in (1,1,254) DO c:\sysinternals\psexec.exe \\192.168.0.%C ipconfig /renew

If you're trying to do this because you staged a new DHCP server, be aware that sometimes Windows clients (not sure if it's all versions or not) will ignore responses from DHCP servers at a different IP than the issuing server until it thinks the the old lease expired or is forcefully released and then renewed. Also, if you run them all at once, having this many clients in sync could be a little annoying for DHCP server load purposes until they drift, but shouldn't really be that bad for 500 nodes.

[-]

Binestar@reddit

Is this an X-Y problem? Why are you doing it? Are you changing the network settings? the netmask? The entire range?

Preferably you would lower the Lease Duration on your DHCP server to something low like 5-10 minutes. Let the existing reservations timeout. When you're ready to make the change, do so and let the reservations renew on the new range.

Use your RMM to send a script? Reboot switches?

[-]

ThatBCHGuy@reddit

Use your configuration managment tool to release renew.

[-]

kyleharveybooks@reddit

Change the vlan on your switch for the new scope… then shut no shut the ports.

[-]

Darkace911@reddit

Power outage! Throw the main breaker! The real answer is to change your DHCP timings to 8 hours, you can delete reservations if they are set to something dumb like 7 days if you are in a hurry.

[-]

Eiodalin@reddit

What is your current DHCP Lease expiry set for?

[-]

kona420@reddit

Identify all uplink ports, use python to loop through port by port and bounce link state.

[-]

discgman@reddit

add Logon script to release and renew ip address for everyone. Force everyone to reboot. Leave it on for a day or so then disable.

[-]

Fit_Prize_3245@reddit

Turn off your switches

[-]

DJDoubleDave@reddit

If we knew what circumstances make this necessary it would inform the answer. Are you changing the address scheme? Trying to push out new DHCP scope options? Something else?

The easiest way is of course to do nothing and wait for the lease time. This isn't a thing you typically need to do manually. If you're planning a future time sensitive change, you can temporarily turn that lease time way down, but you need to do that early enough for the the existing leases to expire so everyone gets the new, shorter lease.

The quickest way will probably be to push out a script with whatever endpoint management system you use.

[-]

MoreTHCplz@reddit

You should really just switch everyone to IPv6 while you are at it

[-]

mauiadmin@reddit

Using GPO: Deploy autotask every hour with a ps1 inside. Ps1 with this line "ipconfig release && ipconfig renew". Intune: you cab deploy the ps1 as app or use a remediation.

[-]

BrainWaveCC@reddit

Because?

[-]

pentangleit@reddit

A lot of people here assuming you only have 100% DHCP clients on your network.

[-]

Ruachta@reddit

Make whatever DHCP changes you need to make. Then depending on your management platform I would do the following on all access ports on all switches. Our environment is all 48's with the trunk on higher ports.

interface range GigabitEthernet1/1/1 - 1/1/48
shutdown
no shut

[-]

hobovalentine@reddit

Context?

Why do you need all clients to renew their IP address?

[-]

apalrd@reddit

- Add new IP prefix to Router Advertisement, apply, wait a bit to let clients pick up their new IP and start using both prefixes at the same time

- Set old IP prefix in Router Advertisement config to set Valid to zero seconds, apply, let clients deprecate their old IP and stop using it

- Once clients have forgotten their old IP, you can remove it entirely from the RA config, and remove routes to it as well

[-]

TravelingNightOwl@reddit

gif

Do you want to provide some context here? What is the driving force behind wanting/needing clients to renew their IP address?

[-]

illicITparameters@reddit

Change the lease time on your current scope to 2 minutes, let all the clients get the new lease time, make the new scope, delete old scope. Done.

[-]

konoo@reddit

I have used Connectwise Control in the past to execute a function like this.