For various applications, such as LSP traceroute, packets must pass through the network processor while on their way to the control CPU. When the packets exit the control CPU in the egress direction, the network processor inserts a timestamp inside each packet. Only packets processed by the control CPU will receive a timestamp.
When interpreting these timestamps, care must be taken because some nodes are not capable of providing timestamps, as such timestamps must be associated with the same IP address that is being returned to the originator to indicate which hop is being measured.