Juniper: CRC error counter on VDSL interface goes up and down

This article explains the behavior of the CRC error counter on VDSL interfaces on SRX devices. This counter does not always increase; it can go down or restart at zero.

In the output of the command “show interfaces at-1/0/0 extensive”, information about CRC errors is reported:

Example:

Example:

root@test> show interfaces at-1/0/0 extensive
...
ADSL Statistics:                    ATU-R                    ATU-C 
                         Interleave        Fast   Interleave        Fast
    CRC               :           0        7673            0           0
...

In subsequent checks of the CRC counter values, it may be seen that the value has decreased or has a value of zero.

Glossary:
ATU-R – ADSL Termination Unit – Remote
ATU-C – ADSL Termination Unit – Central (Office)
Interleave – Interleave channel
Fast – Fast channel
CRC – Cyclic redundancy check

The CRC counter shown in output of the command “show interfaces at-1/0/0 extensive” is not a cumulative counter. Instead, it displays the number of CRC errors that have occurred in the last 15 minutes, instead of always counting up.

If no CRC errors have occurred in the last 15 minutes, the CRC counter value will be zero.

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