Psst, hey buddy, wanna
buy a network switch?
Everybody's selling switches today, or so they
say
By Jodi Cohen
Network World, 8/25/97
Switching is hot these days, and every vendor is
trying to cash in on switching's cachet. But with all
the talk about switching, it's sometimes hard to
determine what's really a LAN switch and what
isn't. Analysts say some vendors are confusing
buyers by abusing the term, applying it to products
that range from bridges to routers.
A LAN switch - in its purest form - is a multiport
Layer 2 device that forwards packets at full wire
speed. ''A switch connects traffic based on a very
large-scale integration (VLSI) hardware process
and uses essentially static rules,'' said Thomas Nolle,
president of CIMI Corp., a consultancy in
Voorhees, N.J. By contrast, a router steers traffic
based on its address, using dynamically adaptable
rules.
The switch label sprang up in the LAN industry as a
way to differentiate hubs, which create
shared-media LANs, and another kind of device -
such as Kalpana, Inc.'s EtherSwitch - that connects
traffic based on a static port-to-media access
control (MAC) address association, Nolle said.
Since the introduction of the EtherSwitch in the late
1980's, the industry has understood it - and devices
like it - to be LAN switches.
But building a network loaded with LAN switches
can create broadcast storms, which must be
controlled with routing. And so the Layer 3 switch -
and all the confusion - emerged.
These new ''switches,'' like good ol' LAN switches,
can make forwarding decisions based on the
packet's destination address. But they also have the
intelligence to make decisions based on Layer 3
information stored inside the packet. So these
''Layer 3 switches'' really are not switches at all, but
routers with faster frame-forwarding capabilities.
''By definition, there can be no such thing as a Layer
3 switch,'' said Kevin Tolly, president of The Tolly
Group, a consulting and testing firm in Manasquan,
N.J.
You're not alone
To further muddy the waters, LAN switches are
different from circuit switches - found in telephone
networks - which send voice and data traffic across
a dedicated communication path between the
sender and receiver. Those are more closely akin to
ATM switches, which work in basically the same
way.
Confused? You're not alone. ''We're confusing the
daylights out of everyone, and the poor users are
left scratching their heads,'' said Soni Jiandani,
director of marketing for LAN switching at Cisco
Systems, Inc. ''The lines across the OSI layers are
getting blurred, because everything is called a switch now.''
''There's no doubt that 'switch' is the sexy term of the day, and so no matter
what vendors build, they've got to call it a switch,'' said Frank Hayes, senior
program manager of LAN switching at Cabletron Systems, Inc.
Which is a switch?
If some vendors are calling a multiport bridge a switch and others are calling
a router a switch, who is right?
''It doesn't make a difference what you call the product. All that matters is
whether you are processing the packet at Layer 2 or Layer 3,'' Tolly said.
''If it's at Layer 2, it's a switch, and if it's at Layer 3, it's a router.''
Ah, but it does matter what the device is called - from a marketing
perspective.
''Layer 3 switching is really just a new buzzword for routing,'' said Patrick
Limpach, network services engineer at Case Western Reserve University in
Cleveland. But he pointed out that vendors may sell more gear if they go
with the switch nomenclature.
''If you call it a switch, people will buy it,'' he said. But if you call it a router,
people might worry because their CEO may have read a white paper that
says routers are out and switches are in.''
While senior executives may get caught up in the marketing hype, Limpach
said few engineers are fooled.
''I know what features I'm looking for, and I'm not just going to take any
box with a swizzy-bang name and buy it because it sounds good or it is
painted pretty colors,'' he said.
Melding monikers
But more and more, the most important feature customers are looking for in
a LAN device is a combination of switching and routing. And that helps
explain the fuzzy definition associated with a switch.
''What we're really seeing is the two types of products converging,'' Tolly
said. ''The vendors who previously only sold switches - like Cabletron - are
adding basic Layer 3 capability. And the folks that only sold routers before
- like Cisco - are trying to make them as fast as switches.''
And in so doing, many vendors, such as Bay Networks, Inc., offer
combination products that are being labeled as routing switches. For
example, Bay's Switch Node device sounds like a switch, but is really a fast
IP router.
''The fact is, people just don't want to talk about pure routers anymore
unless referring to the WAN,'' Tolly said. ''When it comes to the campus
LAN, switches, with a variety of different capabilities, will become the
device name of choice,'' he said.
In fact, the reason some vendors are latching onto the switch term is to
detach themselves from the router's negative connotation.
''The term router is getting the same type of negative association that
front-end processor (FEP) got near the end of its life,'' Tolly said. ''In the
beginning, the FEP was this great device because it saved you all kinds of
money by off-loading work from your extremely expensive mainframe, just
as the router was an expensive, powerful box that brought you all kinds of
functionality. And now you can get as much functionality as you need from
much less expensive and faster boxes.''
And in an attempt to steer clear of routing's bruised reputation, vendors
have confused customers by labeling every little LAN device a switch.
But this is not the first time the term ''switch'' has been confused in the
industry. Remember the muddled meaning of switches vs. port switches?
Vendors such as Bytex Corp. offered port switching hubs, which let
customers group certain ports on the same LAN segment. Then when ''real''
LAN switches came on the scene from vendors such as Kalpana, customers
were confused about getting dedicated bandwidth on every port, industry
observers said.
And believe it or not, some of this confusion may be intentional. When there
is confusion in the industry, customers are often forced to cling to their
incumbent vendor for product direction, analysts said. So it may not be in
the best interest of the Big Four internetwork vendors to clarify the definition
of a switch.
The fact is, a true switch operates at - and only at - Layer 2. If the box
offers Layer 3 capabilities, it just ain't a switch. It's a fast router. End of
story. |
