Administrator Guide

Configure the MTU Size on an Interface
If a packet includes a Layer 2 header, the difference in bytes between the link MTU and IP MTU must be enough to include the
Layer 2 header.
NOTE: The system supports jumbo frames by default (the default maximum transmission unit (MTU) is 9416 bytes). To
configure the MTU, use the mtu command from INTERFACE mode.
For example, for VLAN packets, if the IP MTU is 1400, the Link MTU must be no less than 1422:
1400-byte IP MTU + 22-byte VLAN Tag = 1422-byte link MTU
The following table lists the various Layer 2 overheads found in Dell EMC Networking OS and the number of bytes.
The MTU range is from 592 to 9216, with a default of 9216. IP MTU automatically configures.
The following table lists the various Layer 2 overheads found in the Dell EMC Networking OS and the number of bytes.
Table 43. Layer 2 Overhead
Layer 2 Overhead Difference Between Link MTU and IP MTU
Ethernet (untagged) 18 bytes
VLAN Tag 22 bytes
Untagged Packet with VLAN-Stack Header 22 bytes
Tagged Packet with VLAN-Stack Header 26 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 the 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.
NOTE:
When configuring IP MTU on an interface, make sure to set the same or maximum IP MTU value on both ingress
and egress interfaces to make IPv4 traffic flow.
Interfaces 425