I worked for a startup doing a network management product for multiple third-party devices, mostly talking to them over SNMP, and their SNMP agents would fail i

I worked for a startup doing a network management product for multiple third-party devices, mostly talking to them over SNMP, and their SNMP agents would fail in all sorts of amusing ways. Getting stuck in loops instead of sending all the OIDs you're looking for was probably the most common case, and there were a couple that got tripped up on nulls in their data, but there were others that are more exotic, so we ended up maintaining three different libraries to talk to them (plus our trap receiver). Of course you'd find problems in the underlying libraries from time to time as well, like when there was a memory leak, but only under certain high-latency conditions. Then there were things like the Meru devices that added or deleted a field and accidentally renumbered all the following entities in the (clearly auto-generated) MIB, on a minor firmware version update.