How Ethernet MTU handles small IP packets?

[mohammed hashim]

hi,

the minimum Ethernet MTU is 1500 bytes,

if you configure IP MTU to be something like 1200 bytes, then there will be 300 bytes missing ?

when the router want to process this packet, what will happens to these 300 bytes ?

[Nagendra Kumar Nainar · Accepted solution]

Hi Mohammed,

The normal Ethernet MTU is 1500 bytes. It is not the minimum packet size. The minimum Ethernet frame size is 64 bytes. This is to ensure that the CDMA (collision detection mechanism in earlier half duplex media) is able to detect such collision. In case of IPv6, the minimum packet size 1280 bytes.

So in your case, when ethernet switch receives a frame of size 1200 bytes, it simply will forward teh packet.

-Nagendra

[mohammed hashim]

Hi,

it is confusing due to command:

Switch(config)# system mtu ?
<1500-1998> MTU size in bytes

thanks for your answer