setting Jumbo Packets does not change the MTU

Hi,

I have an Action 10GBE "ethernet 6" and the motherboard Intel I219-V "ethernet 4". Ethernet 6 is directly connected to a 10gbe intel interface on a synology ds1817+ NAS which has jumbo 9000 enabled (subnet 172.16.0.0). Ethernet 4 is connected to an Asus AX86u router running Asuswrt-Merlin 386.3_2. That router is also connected to the built in 1gbe interface on the nas as subnet 192.168.0.0.

On this desktop when I set jumbo packets to 9k on both interfaces. it does not change the mtus to 9000 the way it used to on this machine according to netsh interface ipv4 show interface,
Idx Met MTU State Name
--- ---------- ---------- ------------ ---------------------------
3 25 1500 connected Ethernet 4
17 15 1500 connected Ethernet 6
ping -f -l 8972 confirms this. I have another windows 10 desktop that I have set to jumbo packets and the MTU on that machine properly changes to 9000.
I tried restoring this desktop back to the last windows 10 backup in November and the problem existed then (before I upgraded to windows 11).

Trying to force the mtu fails.

netsh interface ipv4 set subinterface 'Ethernet 4' mtu=9014 store=persistent
The parameter is incorrect.
PS C:\Users\Web> netsh interface ipv4 set subinterface 'Ethernet 4' mtu=9000 store=persistent
The parameter is incorrect.
PS C:\Users\Web> netsh interface ipv4 set subinterface 'Ethernet 4' mtu=4000 store=persistent
The parameter is incorrect.

What setting or condition could possibly cause windows 10 and 11 to refuse to switch to mtu 9000 when the network demonstrably supports it?

Thanks

Web

Hi webdove,

The Jumbo Frame max size is vendor specific. Intel say, that if the option is not available or is greyed out, then it is not supported on that device.

If you use single quotes, the netsh command to change the mtu wont work.
Either use double quotes, eg
netsh interface ipv4 set subinterface "Ethernet 4" mtu=9000 store=persistent
Or use the Index number (Idx) of the adapter, eg:
netsh interface ipv6 set interface 17 mtu=1500 store=persistent

If that is not successful, I would consider deleting and rebuilding the network adaptor and/or device driver.

Did you try latest Intel Network Adapter Driver?
Version 26.7 release date 12/14/2021
Intel® Network Adapter Driver for Windows® 10

PR11T said:

Did you try latest Intel Network Adapter Driver?
Version 26.7 release date 12/14/2021
Intel® Network Adapter Driver for Windows® 10

Click to expand...

I do update that driver when notified. I gave up and did a clean install and the Mtu=9000 setting worked fine. The only theory I have at the moment is that the wire shark Ethernet mod causes the problem. In the mean time I am reinstalling my 543 missing apps