Cisco recommends that a subnet to VLAN relationship exist, but you are
correct, it is not necessary, nor is it in practice...
If this was the case, then we would not need expensive switches in addition
to routers to "subnet our network... we would save some money, and simply
buy a router, maybe add some access lists to it, and voila...
A Vlan is an administrative boundry. The purpose is to reduce traffic on
segments, both collision and broadcast, and to provide some security. "most
companies who implement this do so to restrict access via departments..
So I would not teach it as a subnet, but just as it sounds... a Virtual
LAN..
appearing to be an independant lan, but actually is part of an existing
Lan...
Not to hard to understand...
----- Original Message -----
From: "Peter Van Oene"
To:
Sent: Tuesday, July 24, 2001 9:06 PM
Subject: Re: VLAN routing [7:13465]
> I personally feel that the concept of VLANs, simple as it is, is extremely
> misunderstood by most people in the industry and for that reason, I strive
> to present it accurately. Consider these common questions:
>
> Do I need a router between my VLANs?
> Do I need an IP address on my VLANs?
> Can I route between VLAN 1 and VLAN 2 with just a switch?
> Can I have multiple subnets on the same VLAN?
>
> I've heard these types of questions many times and all of them would be
> reduced if people stopped thinking about VLANs in a layer three context.
If
> one could prevail upon students the concepts of collision and broadcast
> domains and the role routers play in bounding and interconnecting them,
the
> concept of VLANs would be a very logical next step. Telling people that
> VLANs are subnets simply confuses the matter and in reality is anything
but
> the truth. Certainly a one to one mapping of VLANs to IP subnets would be
> ideal, but is not always the case nor is a requirement.
>
> In IP training, I do see the value of having people think about VLANs
> containing single IP subnets, but I still feel you must make sure people
> understand the exclusivity of the two concepts. IP is still pretty low on
> the chart of most popular protocols in use on end stations last I checked
:)
>
> Pete
>
>
>
> *********** REPLY SEPARATOR ***********
>
> On 7/24/2001 at 5:47 PM Priscilla Oppenheimer wrote:
>
> >At 01:03 PM 7/24/01, Peter Van Oene wrote:
> >>I beg to differ slightly on the concept of VLANS. A VLAN, as I'm sure
you
> >>know, is a broadcast domain and makes no assumption of nor has any
> >>dependance upon layer three protocols.
> >
> >I agree in theory. But in practice a VLAN is an IP subnet (on IP
networks)
> >and it helps to think of it this way when designing and troubleshooting.
I
> >get this from Dan Farkas, CCIE and CCSI, author of switching papers at
> >Certificaton Zone. http://www.certificationzone.com. (No, this is not
> >another ad for that great service. ;-) But Dan says that he encourages
his
> >students to use the terms broadcast domain, subnet, and VLAN
> >interchangeably. It helps them understand traffic flow, etc. I think it
> >might help the poster....
> >
> >Priscilla
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=13690&t=13465
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