And, I suppose (more idle speculation, Bob??) ...
If you had two sets of devices and no need for communication between
those sets, you could theoretically create 2 VLANs with addresses all
within the same subnet (ignoring any possible restrictions in a
particular piece of switch code).
Even then, you *would* be able even to talk TCP/IP between those VLANs,
if unicasts were forwarded by the switch outside the VLAN (and you were
willing to create manual, permanent ARP entries where needed) --
but, they're not. BTW, is this a CISCO-specific implementation
or are there VLAN RFCs that prescribe necessary behavior.
-------------------------------------------------
Tks | <mailto:[EMAIL PROTECTED]>
BV | <mailto:[EMAIL PROTECTED]>
Sr. Technical Consultant, SBM, A Gates/Arrow Co.
Vox 770-623-3430 11455 Lakefield Dr.
Fax 770-623-3429 Duluth, GA 30097-1511
=================================================
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
Peter Van Oene
Sent: Wednesday, January 17, 2001 12:26 PM
To: [EMAIL PROTECTED]
Subject: RE: why is routing needed with VLANs
Just for clarity, VLAN's are a layer 2 concept and IP is of course a
layer 3 (please do not start with the "but what layer is arp again" :)
Despite subnets and VLAN's generally happening on a 1:1 basis in a lot
of theoretical and practical discussions, the two concepts are totally
unrelated and altogether unaware of each others presence. An IP host
will not detect a node is on another VLAN and hence send to the gateway,
it will detect a node is on another subnet. It doesn' t really care if
the node is in the same broadcast domain or halfway around the world, if
its not on the network, its sent via the gateway. This is very strict
behavior. Nodes on different IP subnets do not communicate directly in
any case without the use of an intermediary, layer 3 device.
VLANs as a concept are of trivial complexity. VLAN membership,
particularly dynamic membership along with protocols like 802.1q, ISL,
PVST etc that leverage and support VLANs do offer some element of
challenge and opportunity for best practise designs.
I just felt that the line between VLANs (broadcast domains) and IP
subnets was getting somewhat blurry when it really shouldn't be.
_________________________________
FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html
Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
