Changing Packet Encapsulation Type and MTU

The MTU and the encapsulation type of an IP packet can be changed from the default values.

The entire IP packet, including the source and destination address and other control information and the data, is placed in the data portion of the Layer 2 packet. Typically, an Ethernet network uses one of two different formats (encapsulation types) of Layer 2 packet:

Ethernet II

Ethernet SNAP (also called IEEE 802.3)

The control portions of these packets differ slightly. All IP devices on an Ethernet network must use the same format. RUCKUS Layer 3 devices use Ethernet II by default. You can change the IP encapsulation to Ethernet SNAP on individual ports if needed.

You can change the MTU globally, or an individual ports:

Global MTU: The default MTU value depends on the encapsulation type on a port and is 1500 bytes for Ethernet II encapsulation and 1492 bytes for SNAP encapsulation.

Port MTU: A port default MTU depends on the encapsulation type enabled on the port.

The default MTU is 1500 bytes for Ethernet II packets and 1492 for Ethernet SNAP packets. You can increase the MTU size to accommodate jumbo packet sizes up to 10,200 bytes. When jumbo mode is enabled, the maximum Ethernet MTU sizes are as follows:

10,178 bytes: The maximum for Ethernet II encapsulation (Default MTU: 9216)

10,174 bytes: The maximum for SNAP encapsulation (Default MTU: 9216)

Note: For ICX 7850 devices, the maximum jumbo frame size supported is 9380. When jumbo mode is enabled, the maximum ethernet MTU size is 9358 bytes.

In this task the encapsulation type of Ethernet SNAP is configured on Ethernet interface 1/1/1 and jumbo packet sizes are allowed.

Enter global configuration mode.
```
device# configure terminal
```

Increase the MTU size to allow jumbo packet sizes.
```
device(config)# jumbo
```

Enter interface configuration mode.
```
device(config)# interface ethernet 1/1/1
```
The interface is configured as Ethernet interface 1/1/1.

Change the encapsulation type to Ethernet SNAP
```
device(config-if-e1000-1/1/1)# ip encapsulation snap
```
All devices connected to the Layer 3 device port must use the same encapsulation type.

Return to global configuration mode to save the configuration.
```
device(config-if-e1000-1/1/1)# exit
```

Save the configuration to enable the global MTU change to allow jumbo packet sizes.
```
device(config)# write memory
```

Return to privileged EXEC mode.
```
device(config)# end
```

Reload the software to enable the MTU parameter change.
```
device# reload
```

The following example configures the packet encapsulation type to be Ethernet SNAP and allows jumbo packets sizes.

device# configure terminal
device(config)# jumbo
device(config)# interface ethernet 1/1/1
device(config-if-e1000-1/1/1)# ip encapsulation snap
device(config-if-e1000-1/1/1)# exit
device(config)# write memory
device(config)# end
device# reload

IP Addressing

Changing Packet Encapsulation Type and MTU