Selective Packet Discard (SPD)
Overview Selective Packet Discard (SPD) is a mechanism to manage the process level input queues on the Route Processor (RP). The goal of SPD is to provide priority to routing protocol packets and other important traffic control Layer 2 keepalives during periods of process level queue congestion. Historically, on platforms such as the Cisco 7x00 and non-Cisco Express Forwarding (CEF) 7500 systems, significant numbers of transit packets were forwarded by the Route Processor in order to populate the fast switching cache. Consequently, SPD was required in this case to prioritize the routing protocol packets over the transit packets which share the same queue. Currently, on the Cisco 12000 Series Internet Router and on the 7500 running CEF, only traffic destined to the router itself is sent to process level. In this case, SPD is used to prioritize routing protocol packets when management traffic such as Simple Network Management Protocol (SNMP) is present or when a Denial of Service...