Everything I've read on Cisco's site on this matter says to up the cam table time out(mac address aging) to 14400, which matches the arp timeout. Dynamic entries will not.I am trying to overcome a unicast flooding problem caused by asymetrical routing, a by product of the server-farm being on one vlan and users on another. Static entries will persist through a reboot.A MAC address table is made up of the following columns:.If the layer 2 MAC address is unknown, the frame is flooded to all ports except the one from which it originated.If the address is known, the frame is forwarded only on that port.Switches determine which port a frame must be sent out to reach its destination.The reason fragment-free switching stores only the first 64 bytes of the frame is that most network errors and collisions occur during the first 64 bytes of a frame.Fragment-free switching can be viewed as a compromise between store-and-forward switching and cut-through switching.Fragment-free switching works like cut-through switching with the exception that a switch in fragment-free mode stores the first 64 bytes of the frame before forwarding.A cut-through switch reduces delay because the switch begins to forward the frame as soon as it reads the destination MAC address and determines the outgoing switch port.The switch looks up the destination MAC address in its switching table, determines the outgoing interface port, and forwards the frame on to its destination through the designated switch port.With cut-through switching, the LAN switch copies into its memory only the destination MAC address, which is located in the first 6 bytes of the frame following the preamble.Store-and-forward switch operation ensures a high level of error-free network traffic, because bad data frames are discarded rather than forwarded across the network.Store-and-forward switches store the entire frame in internal memory and check the frame for errors before forwarding the frame to its destination.LAN switches are characterized by the forwarding method that they support, such as a store-and-forward switch, cut-through switch, or fragment-free switch.If a VLAN is not specified, the aging specification applies to all VLANs.Entering the value 0 disables the MAC aging.
The range is from 0 to 1000000 the default is 300 seconds.The MAC aging time specifies the time before an entry ages out and is discarded from the MAC address table.You can also configure MAC aging time in interface configuration mode or VLAN configuration mode.You can configure the amount of time that an entry (the packet source MAC address and port that packet ingresses) remains in the MAC table.These static MAC entries are retained across a reboot of the switch.You can also enter a MAC address, which is termed a static MAC address, into the table.The switch then forwards subsequent frames to a single LAN port without flooding all LAN ports.When the destination station replies, the switch adds its relevant MAC source address and port ID to the address table.When the switch receives a frame for a MAC destination address not listed in its address table, it floods the frame to all LAN ports of the same VLAN except the port that received the frame.The switch dynamically builds the address table by using the MAC source address of the frames received.
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