Finding Max MTU size

[BTRY B 529th FA BN]

So I searched a little on finding my Max MTU size. Did my tests and I'm a little confused

ping www.google.com -f -l 1500
Packet needs to be fragmented but DF set.

I get to 1470. I go up to 1472 and that's the highest MTU I have before it gets fragmented.

Instructions say to add 28 to my Max MTU size but that brings me back to 1500 which should be the Max MTU, but when I ran the test at 1500 it said 'Packet needs to be fragmented but DF set.' That's where I'm confused. Is my Max MTU 1472 or 1500 ?

 

[VirtualLarry]

Are you on DSL by any chance?

 

[BTRY B 529th FA BN]

Are you on DSL by any chance?

No, Cable

 

[VirtualLarry]

Cable Internet should have an MTU of 1500. Do you have a router in-between your PC and cable modem? Consider, for testing, connecting your PC directly to your cable modem, set network type to "Public", and then do the same test. If it's not 1500, something is very wrong. If it is, then you know that your router is mis-configured.

 

[mxnerd]

Not familiar with the topic,

but found and article from Microsoft blog.

https://blogs.technet.microsoft.com/runcmd/mtu-size-matters/