Interface Configuration Guide 7705 SAR Interfaces
Edition: 01 3HE 11011 AAAC TQZZA 369
loopback
Syntax loopback {line | internal} {timer {0 | 30 .. 86400} | persistent} [swap-src-dst-mac]
no loopback
Context config>port>ethernet
config>port>dsl
config>port>gpon
Description This command configures timed line loopbacks on Ethernet and GPON network and access
ports, timed line loopbacks on ring Ethernet network ports, untimed line loopbacks on
Ethernet and GPON access ports, and timed and untimed internal loopbacks on Ethernet
ports, DSL ports, and GPON ports.
For Ethernet and GPON ports, a line loopback loops frames received on the corresponding
port back towards the transmit (egress) direction inside the network processor. Line
loopbacks are supported on ports configured in network or access mode.
You can swap the source and destination MAC addresses of the received frames using the
swap-src-dst-mac keyword. The swap-src-dst-mac keyword is not supported on ring
Ethernet ports, GPON ports or DSL ports.
An internal loopback loops the frames that are coming in an egress direction from the fabric
towards the framer, back to the fabric. This type of loopback is usually referred to as an
equipment loopback. Internal loopbacks are supported on ports configured in access mode.
Loopback timers can be configured for 30 s to 86400 s. All non-zero timed loopbacks are
turned off under the following conditions: an adapter card reset, DSL module reset, GPON
module reset, an activity switch, or timer expiry. Line or internal loopbacks can also be
configured as a latched loopback by setting the timer to 0 s, or as a persistent loopback with
the persistent keyword. The persistent keyword is not supported on GPON ports or DSL
ports.
Latched and persistent loopbacks are enabled indefinitely until turned off by the user. Latched
loopbacks survive adapter card resets and activity switches, but are lost if there is a system
restart. Persistent loopbacks survive adapter card resets and activity switches and can
survive a system restart if the admin-save or admin-save-detail command was executed
prior to the restart. Latched (untimed) persistent loopbacks can be enabled only on Ethernet
access ports.
If a loopback exists on a port, it must be disabled or the timer must expire before another
loopback can be configured on the same port. An Ethernet or DSL loopback cannot be
configured on a port that has EFM-OAM enabled on it; EFM-OAM cannot be enabled on a
port that has an Ethernet loopback enabled on it. EFM-OAM is not supported on GPON ports.
Persistent loopbacks are the only Ethernet loopbacks saved to the database by the
admin-save and admin-save-detail commands.
The no form of this command disables the specified type of loopback.
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