VLANs and Trunking explained

A VLAN is a set of workstations within a LAN that can communicate with each other as though they were on a single, isolated LAN.

Among other things, it means that:

• broadcast packets sent by one of the workstations will reach all the others in the VLAN
• broadcasts sent by one of the workstations in the VLAN will not reach any workstations that are not in the VLAN
• broadcasts sent by workstations that are not in the VLAN will never reach workstations that are in the VLAN
• the workstations can all communicate with each other without needing to go through a gateway. For example, IP connections would be established by ARPing for the destination IP and sending packets directly to the destination workstation ---- there would be no need to send packets to the IP gateway to be forwarded on.
• the workstations can communicate with each other using non-routable protocols.

Configuring the VLAN on all ports of a Cisco 4948 switch

Whenever a new switch is connected to the Corporate network ( whether a direct link or a daisy chain ), the VLAN ID should match the expected value.  Or else the Corporate IT folks will disable the port. The VLAN ID for the 10.133.96.0/23 network is 3001. Configure the switch accordingly: switch> enable switch # conf t switch(if-config)#  switch(if-config)# vtp mode transparent switch(if-config)#  switch(if-config)# int range GigabitEthernet1/0/1-48 switch(if-config-range)# switch(if-config-range)# switchport access vlan 3001 switch(if-config-range)# switch(if-config-range)# copy running-config startup-config switch(if-config-range)# switch(if-config-range)# exit switch(if-config)#  switch(if-config)# exit switch #  switch #