Reference Guide

Interfaces | 585
• 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.
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.
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.
negotiation auto
c e s z
Enable auto-negotiation on an interface.
Syntax
negotiation auto
To disable auto-negotiation, enter no negotiation auto.
Defaults
Enabled.
Command Modes
INTERFACE
Command History
Table 18-3. 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
Version 8.3.11.1 Introduced on the Z9000.
Version 8.1.1.0 Introduced on E-Series ExaScale
Version 7.6.1.0 Introduced on S-Series