My Netwok Dictionary

DHCP snooping is a security feature for filtering untrusted DHCP messages, and can protect clients on the network from peering up with an unauthorized DHCP server. When enabled, it builds a table of MAC address, IP address, lease time, binding type, and interface information .

There is also an important difference between trusted and untrusted interfaces when talking about DHCP snooping. . An untrusted interface is an interface that is configured to receive messages from outside the network or firewall. A trusted interface is an interface that is configured to receive only messages from within the network. Read the rest of this entry »

Switched network creates one broadcast domain, similar to that of a VLAN powered network where all nodes belonging to the same VLAN are part of the same broadcast domain, receiving all broadcasts sent on their network.

Broadcasts can actually create problems by flooding the VLAN network.

Because the trunk links interconnecting network switches will carry these broadcasts to every switch in the network.

A switch must forward broadcast frames out all available ports in the broadcast domain because broadcasts are destined everywhere there is a listener. Read the rest of this entry »

The job of VTP is best explained from the perspective of the VTP server. All switches, by default, are VTP servers. The VTP server is where you would create, remove, or modify VLANs.
This VTP server sends an advertisement, across the domain, every 5 minutes or whenever a change is made in the VLAN database. That advertisement contains all the different VLAN names, VLAN numbers, what switches have ports in what VLANs, and a revision number. Whenever a switch receives an update with a larger revision number than the last one it applied, it applies that revision.
Keep in mind that VTP is a Cisco proprietary protocol. So, to use VTP between your switches, you must have all Cisco switches. Read the rest of this entry »

The purpose of the Spanning Tree Protocol (STP) is to prevent loops on a switched or bridged network. STP is enabled on Catalyst 1900 series switches by default. In fact, one instance of Spanning Tree is enabled for each and every VLAN.

The cost or priority of a switch interface is changed using the spantree command from interface configuration mode. Notice that the cost associated with a port can range between 1 and 65536, while the priority of a port can be set to any number between 0 and 255. Read the rest of this entry »