Configure Maximum Transmission Unit Size of Fast Ethernet Interface

C

Example 1: Reset the MTU size to 1492 at the fe-0/0/2 interface.

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user@srx# set interfaces fe-0/0/2 unit 0 family inet mtu 1492

Example 2: To change the family ISO MTU to 1492 use the following command:

Juniper# set interfaces ge-1/0/2 unit 0 family iso mtu 1492

The correct command to configure the maximum transmission unit (MTU) size of a fast Ethernet interface is option A, which is:

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set interfaces fe-0/0/0 unit 0 ethernet-options mtu 1200 

Here's a detailed explanation of the command and why it's the correct choice:

• set interfaces: This is the command to configure an interface on a Junos device.
• fe-0/0/0: This is the name of the interface we want to configure. "fe" stands for Fast Ethernet, "0/0/0" is the interface number.
• unit 0: This specifies that we want to configure the first logical interface on the physical interface. For Fast Ethernet interfaces, this is always unit 0.
• ethernet-options: This sub-command is used to configure Ethernet-specific options.
• mtu 1200: This is the option to set the maximum transmission unit (MTU) size of the interface to 1200 bytes.

Option B, set interfaces fe-0/0/0 mtu 1200, is not the correct command because it doesn't specify which unit of the interface to configure. Without the unit number, the command will not be accepted by the device.

Option C, set interfaces fe-0/0/0 unit 0 mtu 1200, is a valid command to configure the MTU, but it doesn't specify that we want to configure Ethernet-specific options. While it will likely work in this case, it's always better to be as specific as possible when configuring Junos interfaces.

Option D, set interfaces fe-0/0/0.0 mtu 1200, is not the correct command because ".0" refers to a logical subinterface, not the physical interface. For Fast Ethernet interfaces, the logical subinterface is always unit 0.