Interface MTU Setting

When nodes are properly communicating, use the default MTU value. Two nodes on both ends of a link must use the same MTU value so that they can properly operate protocols, such as OSPF and IS-IS, and successfully forward packets.

To change an interface MTU, run the mtu mtu-value command in the interface view. For information about MTU settings' impact on packet transmission is up to traffic type, interface type and board type.

Each interface on NetEngine 8000 F has a default interface MTU value. Table 1 lists interface default MTUs on NetEngine 8000 F.

**Table 1** Interface default MTUs
Interface Type	Default MTU Value (Bytes)	Value Range (Bytes)	Description
Ethernet interface Ethernet sub-interface	1500	46 to 1500	The MTU of an Ethernet interface/sub-interface takes effect only on Layer 3 traffic. NOTE: An Ethernet interface and its sub-interface work at Layer 3 by default and send only Layer 3 traffic. After the portswitch command is run on the Ethernet interface, the Ethernet interface and its sub-interfaces work at Layer 2 and send only Layer 2 traffic.
Eth-Trunk interface Eth-Trunk sub-interface	1500	46 to 9600	The MTU of an Eth-Trunk interface/sub-interface takes effect only on Layer 3 traffic. NOTE: An Eth-Trunk interface and its sub-interfaces work at Layer 3 by default and send only Layer 3 traffic. After the portswitch command is run in the Eth-Trunk interface view, the Eth-Trunk interface and its sub-interfaces work at Layer 2 and send only Layer 2 traffic. The interface MTU must be changed in the Eth-Trunk interface view or sub-interface view, not the member interface view. After a member interface is added to an Eth-Trunk interface, the Eth-Trunk interface MTU automatically takes effect on the member interface. When the Eth-Trunk interface MTU changes, member interfaces automatically synchronize their MTU values with the Eth-Trunk interface MTU. The MTU values on both ends of an Eth-Trunk link must be the same. An MTU inconsistency may cause a service interruption.
GE interface, 10GE interface 25GE interface, 50GE interface, 100GE interface GE sub-interface, 10GE sub-interface, 25GE sub-interface, 50GE sub-interface, 100GE sub-interface	1500	46 to 9600	The MTU of a GE interface/sub-interface takes effect only on Layer 3 traffic. NOTE: A GE interface and its sub-interfaces work at Layer 3 by default and send only Layer 3 traffic. After the portswitch command is run in the GE interface view, the GE interface and its sub-interfaces work at Layer 2 and send only Layer 2 traffic.
Tunnel interface	1500	46 to 9600	Generally applied only to LDP over TE scenarios.
VLANIF interface	1500	46 to 9600	MTUs on VLANIF interfaces take effect only on Layer 3 IP traffic.
Virtual-Ethernet interface	1500	960 to 1518	The MTU of a VE interface takes effect only on Layer 3 traffic. A VE interface works at Layer 3 by default and sends only Layer 3 traffic. After the portswitch command is run, the VE interface works at Layer 2 and sends only Layer 2 traffic.
Virtual-Template interface	1500	328 to 9600	The MTU configured in the VT is used in the LCP phase. Two PPP nodes exchange packets to negotiate and select the smaller one between two configured MTUs as the effective MTU.