Cisco – Should the MAC Tables on a switch Stack be the same between sessions

Unmanaged switches — These switches have no configuration interface or options. They are plug-and-play. They are typically the least expensive switches, found in home, SOHO, or small businesses. They can be desktop or rack mounted.

Managed switches — These switches have one or more ways, or interfaces, to modify the operation of the switch. Common management methods include: a serial console or Command Line Interface accessed via telnet or Secure Shell; an embedded Simple Network Management Protocol SNMP agent allowing management from a remote console or management station; a web interface for management from a web browser. Examples of configuration changes that one can do from a managed switch include: enable features such as Spanning Tree Protocol; set port speed; create or modify VLANs, etc.

Two sub-classes of managed switches are marketed today:

Smart (or intelligent) switches — These are managed switches with a limited set of management features. Likewise "web-managed" switches are switches which fall in a market niche between unmanaged and managed. For a price much lower than a fully managed switch they provide a web interface (and usually no CLI access) and allow configuration of basic settings, such as VLANs, port-speed and duplex.[10]

Enterprise Managed (or fully managed) switches - These have a full set of management features, including Command Line Interface, SNMP agent, and web interface. They may have additional features to manipulate configurations, such as the ability to display, modify, backup and restore configurations. Compared with smart switches, enterprise switches have more features that can be customized or optimized, and are generally more expensive than "smart" switches. Enterprise switches are typically found in networks with larger number of switches and connections, where centralized management is a significant savings in administrative time and effort. A Stackable switch is a version of enterprise-managed switch.

Source: http://en.wikipedia.org/wiki/Network_switch

I would explain in more personal detail, but the wiki explains it pretty well.

A quick prequel-

ARP table - A L3 device (router, host, etc) maintains a mapping between a given IP address and a corresponding MAC address.

CAM table - This may be known by other names in particular switch platforms, but the upshot is that a given L2 switching device maintains a mapping between a given hardware address and one or more physical switch ports.

What's happening in the case above is called unicast flooding. This is a condition where the router still has a live ARP entry even though the switch's CAM table has flushed the corresponding entry. As a result, when the router receives a packet for a given host it is simply forwarded to the switch without first sending an ARP request (the IP : MAC mapping is still cached). The switch, however, no longer knows the port to which this MAC address is mapped (this entry having been aged out earlier). If the switch doesn't have a CAM entry for a given unicast MAC then it will flood packets for that MAC to all ports until it sees a response (i.e. the response to an ARP request).

For obscure reasons ARP and CAM timers are generally quite different on Cisco switches. The values vary somewhat but the mismatch continues through the most modern Nexus devices. Best practice is to set the ARP and CAM timers to similar values - ideally with the CAM table set to 5 seconds or so longer than ARP. It's better for the router to re-ARP than for the switch to have to flood. Setting both values to ~600 seconds (10 minutes) generally isn't too bad, but some environments might want to go a bit longer if excessive ARP traffic is seen on the router.