IP switching mechanisms support two general modes, per-packet and per-destination. The following table outlines the advantages and disadvantages of both modes.
| Per-Destination | Per-Packet | |
|---|---|---|
| IP Switching Mechanism | Fast switching and Cisco Express Forwarding per-destination. | Process switching and Cisco Express Forwarding per-packet. |
| Advantages | With fast switching, packets for a given destination are guaranteed to take the same path even if multiple paths are available. With Cisco Express Forwarding switching, packets for a given source-destination host pair are guaranteed to take the same path, even if multiple paths are available. Traffic destined for different pairs tend to take different paths. | Path utilization with per-packet load balancing is good because per-packet load balancing allows the router to send successive data packets over paths without regard to individual hosts or user sessions. It uses the round-robin method to determine which path each packet takes to the destination |
| Disadvantages | With fast switching, per destination switching may result in unequal load sharing because packets to one destination always follow the same path. Cisco Express Forwarding switching may result in unequal distribution with a small number of source-destination pairs. Per-destination load balancing depends on the statistical distribution of traffic; load sharing becomes more effective as the number of source-destination pairs increase. | Packets for a given source-destination host pair might take different paths, which could introduce reordering of packets. This is not recommended for Voice over IP (VoIP) and other flows that require in-sequence delivery. |
