net-snmp-xdslctl

The Zyxel VMG4005-B50A xDSL modem does not include native SNMP support. However, root access can be obtained, and the system has a few megabytes of writable space suitable for a custom SNMP agent. net-snmp can be cross-compiled for the platform but it lacks built-in support for ADSL2-LINE-MIB and VDSL2-LINE-MIB.

To my knowledge, the Zyxel-provided GPL source does not include any code that accesses xDSL line statistics programmatically or directly from the chipset.

This module provides a partial, read-only implementation of VDSL2-LINE-MIB by parsing the output of the firmware-included xdslctl tool. The code focuses on extracting key values useful for monitoring tools like LibreNMS.

Much of the MIB boilerplate is generated using mib2c.

VDSL2-LINE-MIB::xdsl2LineStatusAttainableRateDs.13 = Gauge32: 97820000 bits/second
VDSL2-LINE-MIB::xdsl2LineStatusAttainableRateDs.14 = Gauge32: 86353000 bits/second
VDSL2-LINE-MIB::xdsl2LineStatusAttainableRateUs.13 = Gauge32: 37302000 bits/second
VDSL2-LINE-MIB::xdsl2LineStatusAttainableRateUs.14 = Gauge32: 27095000 bits/second
VDSL2-LINE-MIB::xdsl2LineStatusActAtpDs.13 = INTEGER: 144 0.1 dBm
VDSL2-LINE-MIB::xdsl2LineStatusActAtpDs.14 = INTEGER: 144 0.1 dBm
VDSL2-LINE-MIB::xdsl2LineStatusActAtpUs.13 = INTEGER: 79 0.1 dBm
VDSL2-LINE-MIB::xdsl2LineStatusActAtpUs.14 = INTEGER: 79 0.1 dBm
VDSL2-LINE-MIB::xdsl2LineStatusActProfile.13 = BITS: 02 00 profile17a(6)
VDSL2-LINE-MIB::xdsl2LineStatusActProfile.14 = BITS: 02 00 profile17a(6)
VDSL2-LINE-MIB::xdsl2ChStatusActDataRate.13.xtuc = Gauge32: 37302000 bits/second
VDSL2-LINE-MIB::xdsl2ChStatusActDataRate.13.xtur = Gauge32: 91054000 bits/second
VDSL2-LINE-MIB::xdsl2ChStatusActDataRate.14.xtuc = Gauge32: 26790000 bits/second
VDSL2-LINE-MIB::xdsl2ChStatusActDataRate.14.xtur = Gauge32: 78438000 bits/second
VDSL2-LINE-MIB::xdsl2LInvG994VendorId.13.xtur = STRING: "BDCM"
VDSL2-LINE-MIB::xdsl2LInvG994VendorId.14.xtur = STRING: "BDCM"
VDSL2-LINE-MIB::xdsl2LInvSystemVendorId.13.xtur = Hex-STRING: 21 B2
VDSL2-LINE-MIB::xdsl2LInvSystemVendorId.14.xtur = Hex-STRING: 21 B2
VDSL2-LINE-MIB::xdsl2LInvVersionNumber.13.xtur = Hex-STRING: 21 B2
VDSL2-LINE-MIB::xdsl2LInvVersionNumber.14.xtur = Hex-STRING: 21 B2
VDSL2-LINE-MIB::xdsl2LInvSerialNumber.13.xtur = STRING: "AAXXXXXXXXX-12"
VDSL2-LINE-MIB::xdsl2LInvSerialNumber.14.xtur = STRING: "AAXXXXXXXXX-12"

• Avoiding hardcoded ifIndex values. The module currently assumes used to assume fixed ifIndex values for ptm0 and ptm0.2, based on the observed behavior of the VMG4005 modem. Ideally, this should be determined dynamically by inspecting the interface table and matching names, even though the most appropriate one may not necessarily exist.

  This module now asks net-snmp for ifIndex of ptm0, atm0 and dsl0, in that order. This module will then use the provided ifIndex for its values, and if there is more than one xdslctl 'line' detected it will use the same ifIndex+n.

  • LibreNMS (and likely others) expects an interface with ifType set to vdsl(97) or adsl(94). This can be accomodated in snmpd.conf, for example:

    interface ptm0 97 300000000
    interface ptm0.2 97 300000000
    

• Limited DSL type coverage. The parsing logic has only been tested with VDSL2. Other xDSL types may produce different output, and the module might not parse them correctly.

• The module, and parsing, has not been tested with a bad xDSL connection or an xDSL connection in an errored state. Output may be unexpected and should not be relied upon solely for diagnostics.

• There may be duplicate code with regards to SNMP caching, as I am not familiar with the caching logic in the templates made by mib2c.