FragRequired is a read-only Counter32 counting the number of Fragmentation Needed report frames sent when a packet exceeds path MTU and the sender set the Do Not Fragment bit recorded for this IP host; a value of 4294967294 means the count is unknown rather than a genuine zero. This counter matters to an admin because it isolates a path MTU mismatch that will keep dropping oversized packets until something adjusts MTU or fragmentation settings, letting them see that specific condition trending up without having to sift through every ICMP message the host or pair exchanged, and — since this isi table duplicates the row layout of the MIB's ili table but is sampled and indexed independently — a given host can show different collection intervals in isi than it does in ili. If FragRequired for host 10.4.12.30 starts climbing while other ICMP counters in the same row stay flat, that isolated rise points specifically at a path MTU mismatch that will keep dropping oversized packets until something adjusts MTU or fragmentation settings rather than a general ICMP flood.