ends out an Address Resolution Protocol (ARP) request packet. This packet is a broadcast, SO it is sent out all switch ports. The ARP packet, when encapsulated into a frame, now contains the requesting station's MAC address, SO the switch knows which port to assign as the source. When the destination station replies that it owns the requested IP address, the switch knows which port the destination MAC address is located on (the reply frame will contain the replying station's MAC address). Running the show mac-address-table command on an IOS-based switch displays the table of MAC addresses and corresponding ports. Multiple MAC addresses on a single port usually indicates that the port in question is a connection to another switch or networking device: Switch1-IOS> sho mac-address-table Legend: * - primary entry age - seconds since last seen n/a - not available mac address learn ports 0013.bace.e5f8 dynamic Gi3/4 0013.baed.4881 dynamic Gi3/4 0013.baee.8f29 dynamic Gi3/4 0013.baeb.ff3b dynamic Gi2/41 0013.baee.8e89 dynamic Gi3/4 0013.baeb.01e0 dynamic Gi4/29 0013.2019.3477 dynamic Gi3/4 0013.bab3.a49f dynamic Gi2/39 0013.baea.7ea0 dynamic Gi7/8 0013.bada.61ca dynamic Gi4/19 0013.bada.61a2 dynamic Gi4/19 4 0013.baeb.3993 dynamic Gi3/33 From the preceding output, you can see that if the device with the MAC address 0013.baeb.01e0 attempts to talk to the device with the MAC address 0013 baea. 7ea0, the switch will set up a connection between ports Gi4/29 and Gi7/8. You may notice that I specify the command show in my descriptions, and then use the shortened version sho while entering commands. Cisco devices allow you to abbreviate commands, so long as the abbreviation cannot be confused with another command. Chapter 2: Hubs and Switches This information is also useful if you need to figure out where a device is connected to a switch. First, get the MAC address of the device you're looking for. Here's an example from Solaris: [root@unix /]$ifconfig -a loo: flags=1000849<UP, LOOPBACK, RUNNING, MULTICAST, IPv4> mtu 8232 in