On Sun, 7 Apr 2002, Richard A Steenbergen wrote:
Layer 3 devices usually do a form a load balancing called "equal cost" forwarding. If you have two routes to a single prefix (say you have two physical links), and both have the same routing "cost", packets may be load balanced across those links. Some mechanisms (for example Cisco CEF) can do this on a per-destination (flow-based) basis, to prevent packet reordering.
I seem to remember fast switching was per-destination, and CEF was round robin. But it seems CEF is now per-destination as well in IOS 12.2. Round robin is optional.
But some protocols can't support this, for example UDP or ICMP traceroutes usually don't get grouped into a "flow", so you can see this kind of load balancing in practice on the internet when you get back traceroute answers from different probes on the same hop.
Routers usually don't really take full flow information into account, but only look at the destination IP address or do a hash over some fields. So usually traceroute doesn't behave differently from regular traffic. This link answers the original question for another router vendor: http://www.juniper.net/techpubs/software/junos51/swconfig51-policy/html/poli...