| Mark, I don't know the answers to all of your questions, but ...
As I understand it, the concepts of Class 1, 2 and 3 VLANs do not
imply anything about location - i.e. you can have any class of VLAN
within a hub or across multiple hubs.
The Class 1 VLAN simply means that the VLAN is defined based on
physical location/port (as per the PORTswitch and the current version of the
DECswitch 400).
There are various schemes proposed as to how VLANs will be
identified, including tagging each packet and use of a protocol between
switches to communicate about VLAN membership. (e.g. the DECswitch
400 uses frame tagging.)
Digital is active in the 802.1 committee to standardise VLAN
implementation (and to lobby against Cisco's move to use the 802.10
security standard for VLANs instead).
Regards
Jeannie
(Tech Support, Networks Australia)
|
| ============================================================================
SUBJECT: VIRTUAL LAN VENDORS FEUD OVER PROTOCOLS
SOURCE: InfoWorld Publishing Company via First! by Individual, Inc.
DATE: August 30, 1995
INDEX: [1]
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InfoWorld via First! : A skirmish is brewing between network vendors
trying to establish protocol standards for the next generation of
virtual LANs.
Virtual LANs (VLANs) are becoming popular among corporate users
because they allow efficient traffic separation, provide better utilization of
bandwidth, and alleviate scaling problems by logically segmenting LANs
into subnetworks, so that packets are switched only within the same VLAN.
But vendors supplying VLAN equipment are trying to settle on one
protocol to ensure VLAN interoperability across diverse products.
Thus far, most of that work has focused on a proposed 802.10 standard,
backed by Cisco Systems Inc., that calls for routers to arbitrate
interoperability across VLANs.
But vendors such as Cabletron Systems Inc. and 3Com Corp. are pushing
for a solution that would resolve interoperability at the 802.10 level, in
equipment such as switches and hubs.
The most distinctive feature of the 802.10 standard is both its major
strength and its principal weakness. Called frame tagging, the feature
scans packet addresses before sending packets to their proper
destinations.
This is especially important for security in metropolitan-area LANs,
where users have a higher stake in ensuring that their network traffic
doesn't get misdirected.
"The frame-tagging mechanism is the most significant step we can take
toward VLAN interoperability," said Tony Moraros, product manager for
Cisco's International Operating Standard division.
On the opposite side are those who question the efficiency of 802.10
for the average VLAN, which typically has less stringent security needs.
Wade Appelman, director of advanced products for Cabletron, said frame
tagging is too slow and unnecessary for the typical VLAN. He added
that 802.10 doesn't offer an adequate method for tracking system use and
cost, features that users would expect if they abandoned their telephone
systems for VLAN communication.
"Cisco should be applauded for their efforts, but it's important to
remember that VLAN standardization is still in its infancy," Appelman
said.
3Com was less charitable toward the proposed standard.
"802.10 is absolutely inadequate for people's needs; it's a security
standard, not a VLAN standard," said Andy Gottlieb, director of LAN
internetworking for 3Com.
This disparity of opinions is the biggest obstacle to establishing a
single protocol, according to analysts.
"A more fundamental issue than 802.10 is trying to agree on what a
VLAN is," said K. Karl Shimada, vice president of Rising Star Research, in
Lakewood, Colo. "It sounds trivial, but over two and a half hours at a
standards meeting [in July], with 80 people in the room, we couldn't
even agree on what a VLAN is."
He said it was important to define and standardize VLANs soon,
because Asynchronous Transfer Mode (ATM) LAN emulation vendors will probably
adopt some of those standards into their own protocol development, making it
easier for users to migrate to ATM later.
But a major part of the problem in implementing a new standard is
that some VLAN requirements haven't yet been fully identified, said Michael
Howard, an analyst with Infonetics Research Inc., in San Jose, Calif.
Compounding those issues are plain old politics.
"802.10 is Cisco's scheme," Howard said. "The other vendors don't
want to be seen as just tagging along."
[08-30-95 at 15:10 EDT, Copyright 1995, InfoWorld, File: x0830002.4di]
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