Hello everyone,
Today I will share with you the principles for configuring the MTU of an Ethernet interface.
Basic Principles
Basic principle: The MTU configurations of the Ethernet interfaces on the two interconnected Layer 3 devices must be the same.
Scenario 1: Inconsistent MTU Configurations
If the MTU configurations at the two ends are inconsistent, as shown in the following figure:
A discards the packets that exceed the MTU from B, and B can receive the packets from A.
Scenario 2: Multi-hop Networking
For the following networking:
The 1600-byte packet sent from C to A is divided into two fragments at B and reassembled into one packet at A.
The 1500-byte packet sent from A to C is directly forwarded to C from B. Fragmentation and reassembly are not performed.
Scenario 3: Layer 2 devices are connected in series.
If a Layer 2 device is connected in series, the MTU of the Ethernet interface must be equal to the MTU of the Layer 3 device at both ends. However, the LAN switches of some vendors support the MTU larger than 1500 bytes by default.
Note: Layer 2 devices do not support IP fragment reassembly.
IP Fragmentation/Reassembly Instance
Assume that Host1 sends a 1600-byte IP packet to Host2. The fragmentation on each interface is as follows:
After all the fragments are sent to the destination IP address (Host2), the 1600-byte IP packet sent by Host1 is reassembled.
Note: After IP packets are fragmented, they are reassembled to the destination IP address, not to the peer end.
Configuration
For example: set the MTU value of interface GigabitEthernet 0/0/1 to 1400
<sysname> system-view
[sysname] interface GigabitEthernet 0/0/1
[sysname-GigabitEthernet0/0/1] mtu 1400
That is all I want to share with you! Thank you!
