Reference Guide

mtu
Set the link maximum transmission unit (MTU) (frame size) for an Ethernet interface.
C-Series, E-Series, S-Series, Z-Series, S4810
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 9252. The
S4810 range is 594 to 12000. The default is 1554.
Defaults 1554
Command Modes INTERFACE
Command History
Version 8.3.11.1 Introduced on the Z9000.
Version 8.3.7.0 Introduced on the S4810.
Version 8.1.1.0 Introduced on the E-Series ExaScale.
Version 7.5.1.0 Introduced on the C-Series.
pre-Version
6.2.1.0
Introduced on the E-Series.
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:
• On the C-Series, the IP MTU gets adjusted automatically when the Layer 2 MTU is
configured with the mtu command.
• On the E-Series, you must compensate for a Layer 2 header when configuring IP MTU
and link MTU on an Ethernet interface. Use the ip mtu command.
When you enter the no mtu command, FTOS reduces the IP MTU value to 1536 bytes. On the
E-Series, to return the IP MTU value to the default, enter no ip mtu.
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
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