For my own reference, and in case anyone else wants to know how to extract MAC information from a Cisco switch via SNMP, the string is 17.4.3.1.2 as documented somewhere on the Cisco site. It would be obvious from an snmpwalk, but they output in decimal instead of hex.

There was something else I was going to write down so that I stop forgetting it, but I can't remember what it was.