In class they said a switch port could only be on one vlan, the previous verion of my test prop agreed with that. The new update is saying a switch port can be on multiple vlans. What does Cisco expect? (NB, OLD routers, like 1900s before they were called 1912 and 1924, that only allowed 4 vlans, DID allow putting a switch port on more then one vlan, after warning you).
If you configure a switch port as an "access port", it can carry traffic of only one VLAN. If you configure it as a "trunk port", it can carry traffic of multiple VLANs. For details about access port and trunk port, please refer to the following Cisco paper, or the study guide on fundamentals of switching available for free download at my web site:
The 2900XL series supports three switchport modes: access, trunk and "multi".
MULTI: Set the port to multi-VLAN port mode. The port operates as a nontrunking VLAN interface that transmits and receives nonencapsulated frames. A multi-VLAN port can be assigned to one or more VLANs.
It would appear that this mode was dropped when they designed the 2950 series of switches that succeeded the 2900XL series. My guess is that the multi feature was a little too strange for most folks to support effectively, because it introduced features that don't fit well into the standard model. It allowed you to have multiple vlans in the same ip subnet, which would be partially isolated from each other. For example, if you have two groups of users in a small organization, they could share a cheap DSL gateway and a server, but still be isolated from seeing and accessing each other's PCs. This WITHOUT requiring a more expensive trunk-capable router or server nic. The gateway and server would be put on "multi" ports, and the users on access ports assigned to one or the other vlan. I haven't ever had cause to try this myself, but it looks interesting.