switch port on multiple vlans

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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).



Re: switch port on multiple vlans


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:

Cisco paper:
http://www.cisco.com/univercd/cc/td/doc/product/lan/cat2950/12122ea2/2950scg/swint.htm#wp1056566

Fundamentals of switching (by KPLAB):
http://www.kp-lab.com/download.htm

KPLAB
http://www.kp-lab.com - Free CCNA Study Guide


Re: switch port on multiple vlans


kplab wrote:
Quoted text here. Click to load it
http://www.cisco.com/univercd/cc/td/doc/product/lan/cat2950/12122ea2/2950scg/swint.htm#wp1056566
Quoted text here. Click to load it

The 2900XL series supports three switchport modes: access, trunk and "multi".

http://www.cisco.com/univercd/cc/td/doc/product/lan/c2900xl/29_35xu/cmdref/macrcli.htm#xtocid24729110

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.



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