Here's some text from CCO regarding CEF and using source and destination IPs to map a packet to one of a set of load sharing links:
Configuring Per-Destination Load Balancing Per-destination load balancing is enabled by default when you enable CEF. To use per-destination load balancing, you do not perform any additional tasks once you enable CEF. Per-destination load balancing allows the router to use multiple paths to achieve load sharing. 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. Per-destination load balancing is enabled by default when you enable CEF, and is the load balancing method of choice for most situations. The URL for the above is (watch wrap): http://www.cisco.com/en/US/products/sw/iosswrel/ps1831/products_configuration_guide_chapter09186a00800ca6ca.html#1000956 John Neiberger wrote: > > Priscilla Oppenheimer wrote: > > > > John Neiberger wrote: > > > > > > Tim Champion wrote: > > > > > > > > Could someone please confirm the following to be true > (taken > > > > from CCO): > > > > > > > > "Per-destination load balancing allows the router to > > > distribute > > > > packets > > > > based on the destination address, and uses multiple paths > to > > > > achieve load > > > > sharing. Packets for a given source-destination host pair > > are > > > > guaranteed to > > > > take the same path, even if multiple paths are available. > > For > > > > example, given > > > > two paths to the same network, all packets for > destination1 > > on > > > > that network > > > > go over the first path, all packets for destination2 on > that > > > > network go over > > > > the second path, and so on. Per-destination load balancing > > is > > > > enabled by > > > > default when you start the router, and is the preferred > load > > > > balancing for > > > > most situations." > > > > > > > > It was my understanding that per-destination load > balancing > > > was > > > > based on the > > > > destination address only and not on the source/destination > > > pair. > > > > > > > > If someone could clarify it would be much appreciated. > > > > > > > > Cheers > > > > Tim > > > > > > This probably depends on the switching mechanism in place. > > Fast > > > switching, as I recall, simply caches the outgoing interface > > > for any given destination so it's relying on the destination > > > information only. > > > > Yes, fast-switching caches the outgoing interface for a > > destination. All packets to a particular destination go out > the > > same interface. CEF works that way too if you use the default. > > > > > CEF uses both the source and destination. > > > > I don't think that is true? CEF doesn't look at source > > addresses. > > I just checked this on our 7513 running 12.2(17a). If you use > the command "show ip cef exact-route sourceip destinationip" > you'll see the cached exit interface. If you do this with > several source addresses going to the same destination when > there are multiple paths you'll see that they use different > exit interfaces. > > I wonder if the default behavior has changed as CEF has evolved? > > John > > Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=73026&t=72944 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
