Ideally, the value of these measures should be 0.

Note that if the rate threshold is violated, then the appliance will drop subsequent ICMP packets it receives. To assess the impact of the threshold violation, use the ICMP packets dropped measure. If the value of this measure is very high, its a clear call for a change in the rate threshold.

To view the configured threshold, use the show ns rateControl command. To set/alter this limit, use the set rateControl command.

The IP protocol has a mechanism for signaling that datagrams are too large to pass through an interface on a network path – when a datagram is received on a router or Layer 3 switch interface that is larger than the interface’s MTU, the device sends an Internet Control Message Protocol (ICMP) message to the previous hop device indicating that the datagram needs to be fragmented in order to pass through that interface, as well as the MTU of the interface. The previous hop device breaks the datagram into pieces that are small enough to pass the next hop interface's MTU.

While this mechanism is usually sufficient to allow traffic to continue normally, it does have some drawbacks. The increase in the number of datagrams from fragmenting means Layer 3 routing has that much more work to do in routing decisions. There is always the possibility that another device further along the network path has an interface with an even smaller MTU and requires further fragmentation, and when the destination device for these datagrams eventually receives them, all datagram fragments must be received so it can be reassembled correctly. If all fragments are not received, the entire original datagram is dropped and must be retransmitted by the sending station (and will probably be fragmented in transit again). This is why, the value of this measure should be kept at a minimum.