Q. I am probing a SonicWall firewall with an SNMP probe, and after a period of time the SonicWall stops responding to the SNMP probe. However, it continues to respond to pings. The probe starts working again only after restarting the InterMapper server.
A. We have found that SonicWall firewalls stop responding to InterMapper SNMP requests after a while. Here's the
- InterMapper chooses a single high-numbered port (generally above 32000) as the source port for all its SNMP queries. It continually uses that port until it gets restarted.
- The SonicWall has a built-in limit that, in the past, would cause it to ignore SNMP queries if it got "too many" from the same source port.
Thus, after a while, the SonicWall would stop responding with SNMP, although it would still answer pings.