Iso is a read-only Counter32 giving the number of International Standards Organization (ISO) protocol frames counted for the monitored network; per the MIB a value of 4294967294 means the count is unknown rather than genuinely zero. Because it is broken out on its own instead of folded into a generic IP total, an admin can watch this counter to see how much of the monitored network's traffic is legacy OSI-stack traffic, which is unusual to see on a modern IP network and worth investigating if it appears. If this Iso counter climbs sharply on the segment this probe watches while total traffic stays flat, that shift shows legacy OSI-stack traffic, which is unusual to see on a modern IP network and worth investigating if it appears is displacing whatever other protocol mix was there before.