Hello guys,
I have some questions regarding MTU and the different way to configure it on Cisco devices and I don't find any good documentation on that particular topic.
First of all, what will happen if a device receive a packet larger than the MTU of the receiving interface ? IMHO, it will be silent dropped.
Configuration then. I see several places where the MTU can be configured:
- MTU set on a physical interface - not available on all platforms, sometimes it is a system value
- MTU set on a VLAN - never seen that in a production environment, but the command exists under vlan
- MTU set on an interface VLAN
So, if I apply different values on these different places, what will happen? I know, nothing good, but in detail? I would say that MTU of the interface is used whenever the packet is just L2 forwarded, but what will happen if is routed? Is there any precedence between the different places where the MTU can be applied?
Finally, you can also set the IP MTU on any IP interface - this one is quite simple, unless I'm mistaken : it is the value used to determine if fragmentation is needed or not. Usually, it can't be set to a value greater than the interface MTU.
Thanks in advance for your answers, best regards,
François
