what an interesting topic to write about :-)
rate limiting on a cisco device could be so easy or so hard...
examples:
on a cisco 4900 series switch (L3 switch) rate limiting is done using QoS, policing or shaping.
policing which dealing with excess traffic by dropping it. while shaping is more smooth by putting excess traffic in a buffer for later transmition.
configuration:
SW#conf t
SW()#policy-map
SW(-pmap)#class
SW(-pmap-c)#shape average | percent
or use the following to police:
SW(-pmap-c)#police confirm-action exceed-action
SW(-pmap-c)#interface
SW(-int)#service-policy
SW(-int)#do wr


the same way goes on some routers, like 7600 series.
thank you,
email me: mshak3r@gmail.com