3Com MSR 50, MSR 30 manual Mtu on serial interfaces, Syntax loopback Undo loopback, 197

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loopback

Syntax loopback

undo loopback

View Serial interface view, AUX interface view, AM interface view

Parameter None

Description Use the loopback command to enable internal loopback on the serial interface.

Use the undo loopback command to restore the default.

By default, loopback is disabled.

Loopback is intended for test use. Disable it otherwise.

Example # Enable internal loopback on interface Serial 2/0.

<Sysname> system-view

[Sysname] interface serial 2/0

[Sysname-Serial1/0] loopback

mtu (on serial interfaces)

Syntax mtu size

undo mtu

View Serial interface view, AUX interface view, AM interface view, USB interface view

Parameter size: Maximum transmission unit (MTU) to be set for a serial interface, in the range 128 to 1,500 (in bytes).

Description Use the mtu command to set the MTU for a serial interface.

Use the undo mtu command to restore the default.

By default, the MTU of a serial interface is 1,500 bytes.

Due to the length of Qos queue, a packet may be discarded if the MTU is relatively small and the packet is segmented into too many fragments. You can increase the Qos queue length to avoid this situation. To do so, use the qos fifo queue-lengthcommand in interface view. For details, refer to the “FIFO Queuing Configuration Commands” on page 1809.

The MTU setting can affect IP packets assembly and fragmentation on the interface.