3Com 3C13636 Configuration Manual page 256

3Com Router 3000 Ethernet Family
Configuration Guide
Table 2-3 Configure MTU
Configure MTU
Restore MTU to default
The frame format defaults to Ethernet_II and MTU size is in the range 46 to 1500 bytes.
The default MTU size is 1500 bytes.
Note:
MTU only affects IP packet assembly/disassembly. MTU can reach 1500 bytes in the
Ethernet_II format.
Since QoS queue length is limited, too small MTU and too big packet may result in
many fragments and QoS queues discarding packets. To avoid this, you can increase
QoS queue length. By default, the queue scheduling mechanism adopted on the
interfaces of 3Com Routers is FIFO. You can use the qos fifo queue-length command
to change the queue length. For detailed QoS queue configuration, see the section of
QoS configuration in this manual.
IV. Selecting operating speed of Ethernet interface
Ethernet interfaces support multiple speeds. FE electrical interfaces support 10Mbps
and 100Mbps. FE optical interfaces only support 100Mbps. GE electrical interfaces
support 10Mbps, 100Mbps, and 1000Mbps. GE optical interfaces can only work at
1000Mbps. Thus, you only need to configure Ethernet electrical interfaces while do not
need to configure optical interfaces.
Perform the following configuration in Ethernet interface view.
Table 2-4 Select an operating speed for an Ethernet interface
Select an operating speed for the FE interface
Configure the operating speed for a GE
electrical interface
Restore the default operating speed
By default, negotiation is selected, i.e., the system automatically chooses an optimum
operating speed.
Operation
Operation
3Com Corporation
2-3
Chapter 2 LAN Interface Configuration
Command
mtu size
undo mtu
Command
speed { 10 | 100 | negotiation }
speed { 10 | 100 | 1000 |
negotiation }
undo speed