Appliances send internet control message protocol (ICMP) pings to dynamically monitor uplink state on a regular schedule (the default is 2 seconds). If the ping responses don’t make it back within the timeout period, the probe is considered lost. If the system loses the threshold number of packets, it considers the uplink to be down and triggers an alarm.

Optionally, select a DSCP marking for the ping packet. You must select this option if the service providers are applying QoS metrics based on DSCP marking and each provider is using a different type of metric. Path selection-based DSCP marking can also be used in conjunction with policy-based routing (PBR) on an upstream router to support path selection in cases where the appliance is more than a single Layer-3 hop away from the edge router. The default marking is preserve. Preserve specifies that the DSCP level or IP ToS value found on pass-through and optimized traffic is unchanged when it passes through the SteelHead.