SNMP Monitoring of Zyxel USG FLEX 700H Interfaces (ifSpeed vs. ifHighSpeed)

Zyxel_Kevin

Question:

How to accurately monitor 10Gbps SFP interface speeds on Zyxel USG FLEX 700H using SNMP?

Answer:

The discrepancy in reported speeds and the appearance of unfamiliar interfaces during SNMP polling are due to the specific OID limitations and the internal architecture of the Zyxel USG FLEX 700H.

• Root Cause:
  • ifSpeed OID Limitation: The ifSpeed OID (iso.3.6.1.2.1.2.2.1.5) is an older RFC (RFC-1213) that uses a 32-bit integer. This limits its maximum reported value to approximately 4.29 Gbps (4,294,967,295 bits/second). When an interface's actual speed exceeds this limit (e.g., a 10Gbps SFP interface), it will report this maximum possible value, leading to an inaccurate reading.
• Resolution:
  • For Accurate 10Gbps SFP Interface Speed Monitoring: Use the ifHighSpeed OID (iso.3.6.1.2.1.31.1.1.1.15). This OID is defined in IF-MIB (RFC 2863) and reports the interface's bandwidth in units of 1,000,000 bits/second (Mbps). For a 10Gbps interface, it will correctly report '10000' Mbps.