I have a question about MTU or path MTU. In my setup I have 2 computers (firewall, Windows PC) and one NAS, each with a gigabit interface. They are connected throughout the same gigabit switch. In all of them I configured a MTU of 9000. Also activated "Jumbo Packets" on the interface of the Windows PC.
After measuring the path MTU with nmap I received a weird result:
- When I messure from the NAS to the firewall and to the PC the result is 9000.
- When I messure from the firewall to the PC and to the NAS the result is 9000.
BUT
- When I messure from the PC (Windows firewall on and off) to the firewall and to the NAS the result is 1492.
Do you have an explanation for these weird behavoir?
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Hirsch
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1492 is the default value for windows and ethernet on windows – djdomi Sep 13 '19 at 21:26
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Ok, but I edited the MTU value of my ethernet interface and windows shows me this value in the status of the interface. – Hirsch Sep 13 '19 at 22:26
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With "netsh interface ipv4 show interfaces" Windows shows me the 9000. – Hirsch Sep 14 '19 at 10:28
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i think some device is not ablr to handle jumbo frames, even yozr switch must hsvr the ability to use them – djdomi Sep 14 '19 at 11:07
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It sounds like your PC NIC can't do jumbo frames -- even tho the software says it can. – Ron Trunk Sep 14 '19 at 15:23
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I think that`s not the case. My NIC is an "Intel(R) Ethernet Connection (2) I219-V" and it is suitable for jumo frames (https://ark.intel.com/content/www/us/en/ark/products/82186/intel-ethernet-connection-i219-v.html). – Hirsch Sep 15 '19 at 22:29