Dell C9000 Series Reference Manual page 1196

Version
8.3.19.0
8.3.7.0
8.1.1.0
6.1.1.0
Usage Information When you enter the no mtu command, the system reduces the ip mtu value to 1536
bytes. To return the IP MTU value to the default, use the no ip mtu command.
Compensate for Layer 2 header when configuring link MTU on an Ethernet interface or
the system may not fragment packets. If the packet includes a Layer 2 header, the
difference between the link MTU and IP MTU (the ip mtu command) must be enough
bytes to include for the Layer 2 header.
Link MTU and IP MTU considerations for Port Channels and VLANs are as follows
Port Channels:
•
•
VLANs:
•
•
•
The following describes the difference between Link MTU and IP MTU.
Layer 2
Overhead
Ethernet
(untagged)
VLAN Tag
Untagged Packet
with VLAN-Stack
Header
Description
Introduced on the S4820T.
Introduced on the S4810.
Introduced on the E-Series ExaScale.
Introduced on the E-Series.
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.
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.
Difference between Link MTU and IP MTU
18 bytes
Tag 22 bytes
22 bytes
IPv4 Routing 1196