Command Line Reference Guide

mtu
Set the link maximum transmission unit (MTU) (frame size) for an Ethernet interface.
S5000
Syntax
mtu value
To return to the default MTU value, use the no mtu command.
Parameters
value Enter a maximum frame size in bytes. The range is 594 to 12000. The
default is 1554.
Defaults 1554
Command Modes INTERFACE
Command History
Version 9.0(1.3) Introduced on the S5000.
Usage
Information
If the packet includes a Layer 2 header, the difference between the link MTU and IP MTU (ip
mtu
command) must be enough bytes to include the Layer 2 header:
When you enter the no mtu command, FTOS reduces the IP MTU value to 1536 bytes.
Link MTU and IP MTU considerations for port channels and VLANs are as follows.
port channels:
• All members must have the same link MTU value and the same IP MTU value.
• The port channel link MTU and IP MTU must be less than or equal to the link MTU and
IP MTU values configured on the channel members. For example, if the members have
a link MTU of 2100 and an IP MTU 2000, the port channel’s MTU values cannot be
higher than 2100 for link MTU or 2000 bytes for IP MTU.
VLANs:
• All members of a VLAN must have same IP MTU value.
• Members can have different Link MTU values. Tagged members must have a link MTU
4 bytes higher than untagged members to account for the packet tag.
• The VLAN link MTU and IP MTU must be less than or equal to the link MTU and IP MTU
values configured on the VLAN members. For example, the VLAN contains tagged
members with Link MTU of 1522 and IP MTU of 1500 and untagged members with Link
MTU of 1518 and IP MTU of 1500. The VLAN’s Link MTU cannot be higher than 1518
bytes and its IP MTU cannot be higher than 1500 bytes.
The following shows the difference between Link MTU and IP MTU.
Layer 2 Overhead Link MTU and IP MTU Delta
Ethernet (untagged) 18 bytes
VLAN Tag 22 bytes
Untagged Packet
with VLAN-Stack
Header
22 bytes
509