Hi,
"ip load-sharing per-packet enables per-packet load balancing.
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. Per-packet load balancing ensures balancing over multiple links.
Path utilization with per-packet load balancing is good, but packets for a given source-destination host pair might take different paths. Per-packet load balancing could introduce reordering of packets. This type of load balancing would be inappropriate for certain types of data traffic (such as voice traffic over IP) that depend on packets arriving at the destination in sequence.
Use per-packet load balancing to help ensure that a path for a single source-destination pair does not get overloaded. If the bulk of the data passing through parallel links is for a single pair, per-destination load balancing will overload a single link while other links have very little traffic. Enabling per-packet load balancing allows you to use alternate paths to the same busy destination.
If you want to enable per-packet load sharing to a particular destination, all interfaces that can forward traffic to the destination must be enabled for per-packet load sharing. "
Reference: http://www.cisco.com/en/US/docs/ios/12_1/switch/configuration/guide/xcdcefc.html#wp1000978
"IP Route-Cache
Using the route cache is often called fast switching. The route cache allows outgoing packets to be load-balanced on a per-destination basis rather than on a per-packet basis. The ip route-cache command with no additional keywords enables fast switching.
Entering the ip route-cache command has no effect on a subinterface. Subinterfaces accept the no form of the command; however, this disables CEF or dCEF on the physical interface as well as all subinterfaces associated with the physical interface".
Reference: http://www.cisco.com/en/US/products/sw/iosswrel/ps5207/products_command_reference_chapter09186a0080417d88.html#wp1010901
I hope this helps.
Best regards.
Massimiliano.
