How do I persuade Windows 11 to use the MTU given to it by DHCP (option 26) ?

Question

How do I persuade Windows 11 to use the MTU given to it by DHCP (option 26) ?

GMCH 20

My DHCP server sends option 26 (aka interface-mtu) with value 1492, because that is the MTU of my broadband connection.

Windows 11 ignores this and uses 1500.

I cannot find a setting for "use the MTU provided by DHCP" :-(

Help !!

0 comments

Answer accepted by question author

Quinnie Quoc 10,730 Independent Advisor

Hi GMCH,

I understand the challenge you're facing—especially when your DHCP server is correctly configured to send Option 26 (Interface MTU) with a value of 1492, but Windows 11 continues to default to 1500.

Why This Happens

Unfortunately, Windows does not honor DHCP Option 26 by default. While the DHCP specification allows for MTU configuration via this option, Windows clients have historically ignored it, opting instead to use the default MTU of 1500 unless manually overridden.

Workarounds You Can Try

Manually Set MTU via PowerShell You can explicitly set the MTU for your network interface using PowerShell:

powershell

Get-NetAdapter | Where-Object {$_.Status -eq "Up"} | Set-NetIPInterface -NlMtu 1492

Or target a specific adapter:

powershell

Set-NetIPInterface -InterfaceAlias "Ethernet" -NlMtu 1492

Use Registry to Enforce MTU (Advanced) You can create a registry entry to enforce MTU on a specific interface: Navigate to: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\<InterfaceGUID> Add a DWORD value named MTU and set it to 1492. Be sure to back up your registry before making changes. Use Group Policy or Scripts for Enterprise Environments If you're managing multiple machines, consider deploying a startup script or GPO to enforce MTU settings across clients.

No Native “Use DHCP MTU” Toggle

You're correct—Windows 11 does not offer a native setting to “use MTU from DHCP”, and this behavior has been consistent across Windows versions. If this is a critical requirement for your environment, you might consider submitting feedback via the Feedback Hub or exploring third-party DHCP clients that respect Option 26.

I hope my answer is useful for you.

Best regards,

Quinnie Quoc.

GMCH 20 Reputation points

2025-08-15T10:29:11.1+00:00

Thank you. At least I can now stop search for something I thought surely must exist somewhere... perhaps buried in some arcane registry entry.

RFC 2131 (1997) and its predecessor RFC 1541 (1993) do say that a DHCP client 'MAY' take notice of the MTU option -- not 'SHOULD' and not 'MUST'. But I cannot think of a reason to make it impossible for the user to enable the MTU option.

I have double checked. My broadband router has an MTU discovery widget. It tells me the MTU on the WAN side (ADSL using PPPoA) really is 1492. I believe this is not unusual.

Is this a critical requirement ? Perhaps not. Is it ridiculous that there is no way to enable the DHCP MTU option ? Yes ! Unless, of course, someone can demonstrate that enabling the option is a serious mistake.

On my way to the Feedback Hub to continue howling at this moon.

2 additional answers

Your answer

GMCH 20 Reputation points

2025-08-15T10:29:11.1+00:00

Thank you. At least I can now stop search for something I thought surely must exist somewhere... perhaps buried in some arcane registry entry.

RFC 2131 (1997) and its predecessor RFC 1541 (1993) do say that a DHCP client 'MAY' take notice of the MTU option -- not 'SHOULD' and not 'MUST'. But I cannot think of a reason to make it impossible for the user to enable the MTU option.

I have double checked. My broadband router has an MTU discovery widget. It tells me the MTU on the WAN side (ADSL using PPPoA) really is 1492. I believe this is not unusual.

Is this a critical requirement ? Perhaps not. Is it ridiculous that there is no way to enable the DHCP MTU option ? Yes ! Unless, of course, someone can demonstrate that enabling the option is a serious mistake.

On my way to the Feedback Hub to continue howling at this moon.

Answer 1

GTS-NJ 580 Volunteer Moderator

I have some doubt about the value of changing the MTU in this case, but if you do want to set it manually you may need to also disable autotune for it to stick.

In an elevated command prompt enter netsh interface tcp set global autotuning=disabled

To verifiy the status enter netsh interface tcp show global

GMCH 20 Reputation points

2025-08-20T08:54:00.6866667+00:00

It seems to me to be a good idea to avoid my broadband router having to fragment stuff before it even leaves the premises.

I'm curious as to why you doubt the value of that.

Honestly, I don't really want to set it manually. When the laptop connects to other networks, I would like it to use the locally (hopefully optimal) configured MTU.

I would like to know why Windows doesn't feel like honouring a perfectly standard DHCP option -- or at least providing a way to configure it to do so.

FWIW: from what I read, autotune is messing with TCP window size... whose relationship to the MTU I'm a little hazy on :-(

Answer 2

Hello @GMCH Thank you for reaching out to Microsoft and informed the issue. I believed that you've run into a common issue where Windows 11 ignored the MTU value but fortunately there is a workaround for this issues:

Set MTP manually:

Open Command Prompt as administrator then input "netsh interface ipv4 show subinterfaces"
A list of network will shows up, look for the correct display name and remember it
Open command prompt again and input
- netsh interface ipv4 set subinterface "Your Interface Name" mtu=1492 store=persistent Replace the "Your Interface Name" with the name of your network interface
Then hit Enter

Verify MTU change:

Open Command Prompt and input: netsh interface ipv4 show subinterfaces > Enter
Check the MTU column, if it show 1492 then changes has been made

((Do notice the space between the forward dash (/) in the command)

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

GMCH 20 Reputation points

2025-08-15T08:38:38.6366667+00:00

Thanks, but...

...setting the MTU permanently is something of a kludge :-(

I accept that it would make almost no difference if my laptop always uses MTU=1492, even when connected to a network where 1500 is not an issue.

I won't ask why the MTU isn't settable in (say) the "Advanced TCP/IP" settings.

Share via

How do I persuade Windows 11 to use the MTU given to it by DHCP (option 26) ?

2 additional answers

Your answer