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
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
Tagged Packet with
VLAN-Stack Header
26 bytes
714
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