Administrator Guide

Version Description
9.2(1.0) Introduced on the Z9500.
8.3.19.0 Introduced on the S4820T.
8.3.11.1 Introduced on the Z9000.
8.3.7.0 Introduced on the S4810.
8.1.1.0 Introduced on the E-Series ExaScale.
7.5.1.0 Introduced on the C-Series.
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.
When you enter the no mtu command, the system 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
Tagged Packet
with VLAN-Stack
Header
26 bytes
portmode hybrid
To accept both tagged and untagged frames, set a physical port or port-channel. A port configured this way is identified as a hybrid port in
report displays.
C9000 Series
Syntax
portmode hybrid
To return a port to accept either tagged or untagged frames (non-hybrid), use the no portmode hybrid
command.
Interfaces 693