Chapter 10
| Interface Commands
Interface Configuration
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Example
The following example disables port 5.
Console(config)#interface ethernet 1/5
Console(config-if)#shutdown
Console(config-if)#
switchport mtu This command configures the maximum transfer unit (MTU) allowed for layer 2
packets crossing a Gigabit, 10 Gigabit or 40 Gigabit Ethernet port or trunk. Use the
no form to restore the default setting.
Syntax
switchport mtu size
no switchport mtu
size - Specifies the maximum transfer unit (or frame size) for a Gigabit,
10 Gigabit or 40 Gigabit Ethernet port or trunk. (Range: 1500-12288 bytes)
Default Setting
1518 bytes
Command Mode
Interface Configuration (Ethernet, Port Channel)
Command Usage
â—† Use the jumbo frame command to enable or disable jumbo frames for all
Gigabit, 10 Gigabit and 40 Gigabit Ethernet ports. To set the MTU for a specific
interface, enable jumbo frames and use this command to specify the required
size of the MTU.
â—† The comparison of packet size against the configured port MTU considers only
the incoming packet size, and is not affected by the fact that an ingress port is a
tagged port or a QinQ ingress port. In other words, any additional size (for
example, a tagged field of 4 bytes added by the chip) will not be considered
when comparing the egress packet’s size against the configured MTU.
â—† When pinging the switch from an external device, information added for the
Ethernet header can increase the packet size by at least 42 bytes for an
untagged packet, and 46 bytes for a tagged packet. If the adjusted frame size
exceeds the configured port MTU, the switch will not respond to the ping
message.
â—† For other traffic types, calculation of overall frame size is basically the same,
including the additional header fields SA(6) + DA(6) + Type(2) + VLAN-Tag(4)
(for tagged packets, for untaqged packets, the 4-byte field will not be added by
switch), and the payload. This should all be less than the configured port MTU,
including the CRC at the end of the frame.
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