Low-end Layer 3 switch?

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I need a very low-end Layer 3 switch (or router, but would prefer the
faster speed).  4 ports would be sufficient; 8 or 16 would be great.
10/100 is also sufficient; no need for Gigabit.  Does anyone know of
such a device, either new or a model I should look for on the used
market?

Thanks.

sPh


Re: Low-end Layer 3 switch?


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Just what is the difference between a "switch" doing things at the
network layer and a "router" doing things at the network layer?

I've always been of the understanding that stuff done at layer 3 is
"routing" regardless of what the marketroids call the box.

rick jones
--
The glass is neither half-empty nor half-full. The glass has a leak.
The real question is "Can it be patched?"
these opinions are mine, all mine; HP might not want them anyway... :)
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

Re: Low-end Layer 3 switch?


 
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I know what I think the difference should be, though I don't know
that anyone else has the same definition.

I would say a layer 3 switch should have more special purpose
hardware, such as would be expected in a layer 2 switch.

A router is usually mostly software, with more or less conventional
NICs and a COTS processor.

I understand that one can run Linux on a Linksys WRT54G, for example.  

Similar to the way a layer 2 switch might have a processor to
handle tasks other than packet forwarding, a layer 3 switch might
have a similar processing function.  Packet forwarding should be
done without the involvement of the processor, or with minimal
involvement, other than to update routing tables.

-- glen

Re: Low-end Layer 3 switch?


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So, implementation detail is more important than function?

My understanding is that those big honking "core routers" from the
likes of Cisco, Juniper, Foundry et al are very much special purpose
hardware.

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It seems that one can run some variant of Linux on just about anything
with a clock pulse :)

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By that definition then the really high-end (and probably not quite so
really high end) routers from the vendors would be switches.

rick jones
--
portable adj, code that compiles under more than one compiler
these opinions are mine, all mine; HP might not want them anyway... :)
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

Re: Low-end Layer 3 switch?


  
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As with the old saying, form follows function.  If you can do
it with cheap hardware there is no point in using expensive custom
hardware.  As processors get faster, the dividing line will move.
 
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Probably.  The last time I opened a Cisco router (a lower end
model, about 10 years ago.) I was surprised to see ordinary hardware.
 
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How about the core router mentioned above?
 
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Maybe.  Though the people that buy them probably don't care
what they are called as long as they work up to their
specifications.

-- glen

Re: Low-end Layer 3 switch?


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:) Since there are probably GP "service CPUs" in those things I'd bet
they could - they might even be running Linux there already.

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I've always chalked it up to the salescritters calling something a
switch to make it sound newer and sexier and perhaps easier to manage,
whether it was really easier to manage being an open question.

Of course, at times I think that a switch should _really_ be called a
multi-port bridge :)

rick jones
--
The glass is neither half-empty nor half-full. The glass has a leak.
The real question is "Can it be patched?"
these opinions are mine, all mine; HP might not want them anyway... :)
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

Re: Low-end Layer 3 switch?


 
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If you do, Rich will remind you of the lack of usefulness
for single port bridges.

-- glen

Re: Low-end Layer 3 switch?


glen herrmannsfeldt wrote:

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a single port layer 3 switch (one that routes) between tagged vlans
could be usefull. You could use it to add routing capability between the
vlans on a layer 2 switch...

Hmmm.... perhaps someone should make a small box like that and market it.


Re: Low-end Layer 3 switch?


On Wed, 15 Feb 2006 23:47:24 -0500, snertking

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No reason it cannot be a multi port switch and dont bother to connect
some?

I have done a varient on this several times with a router on the side
of a layer 3 switch.

i used it to add extra routing functions to a layer 3 switch that only
supports IPv4 - Appletalk, OSI and SNA.... usually the switches GigE,
but a router is often limited to 100M and VLANs.

the underlying assumption is that the IP needs to be fast but that the
minority protocols still need to work....

it actually makes a good tool to get people to actually move to IP.

"of course you can use xxx - but if you go to IP then you have access
to much more bandwidth....."
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--
Regards

stephen_hope@xyzworld.com - replace xyz with ntl

Re: Low-end Layer 3 switch?


We used a couple of these ( cisco 3000 using a single t/r
) to act as endpoints in tokenring tunnels..

The staff used to call them "fucking machines", if it was b.cause of
the packets going in and out or if it was the fact that they served
a useful purpose and worked ( in contrast to the big vendors stuff)


Re: Low-end Layer 3 switch?


Rick Jones wrote:

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If it's Cisco it would probably be running some variant of IOS.  But it
might very well have some rather remarkably mundane innards.

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--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)

Re: Low-end Layer 3 switch?


Rick Jones wrote:
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Bridges cannot perform cut-through forwarding.  Switches (more and more
these days) can.

Aside from that, I agree that the major difference seems to be port
density.

/chris


Re: Low-end Layer 3 switch?


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I would have thought it was "less and less these days" rather than
"more and more". You can't do cut-through between different port
rates, broadcasts and multicasts are increasing, increasing port
densities make it more likely that one or more of the destination
ports will be temporarily busy at the time, you can't do rate policing
well with cut-through, you can't do packet inspection security
functions with cut-through, you can't abort transmission of a packet
that is detected as having the wrong CRC, and you can't easily do
port-level authentication such as 802.1X with cut-through. All of
these factors argue for a continuance or increased reliance upon
the queued-packet asynch transmission model rather than the increased
cut-through.

Re: Low-end Layer 3 switch?


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Agreed. Also the fact that speeds have increased - the serialization
delay at gigabit speeds is negligible for normal packet sizes.

I can't remember *any* switch vendor which boasts about cut-through
forwarding these days.

Steinar Haug, Nethelp consulting, sthaug@nethelp.no

Re: Low-end Layer 3 switch?


Walter Roberson wrote:
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Allow me to clarify :-)

I didn't mean that the cut-through model applied to more and more of
today's Ethernet traffic.

I meant that while not *all* switches support the cut-through model,
that support for it is more common than it was, say, 10 years ago.

The reason for my post was to assert that there *is* a distinction
between a bridge (which by definition does not support cut-through) and
a switch (which may support it).  The text you snipped implied that
bridges and switches are the same thing.  They're not.  I have no
opinion on whether cut-through forwarding is a useful feature given the
requirements of your network.

15 posts into this thread, it's starting to look like the OP has gotten
his answer:  Nobody knows of a pocket-sized layer 3 switch.

...We'd just rather argue the semantics of what it means to "switch",
whether a one-armed switch might be useful, and whether the it's better
to store-and-forward because it allows you to do tricks that are
impossible otherwise.

:-)

/chris


Re: Low-end Layer 3 switch?


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"(more and more these days)" implies that the number of such switches
is still increasing.

The last time I saw a general-purpose cut-through switch being
advertised was...  I dunno. 7 years ago, maybe longer. I might have
heard of a special-purpose cut-through switch 5 years ago. I
can't think of a single one on the market now, but there are
thousands and thousands of switch manufacturers and I don't pretend
to know them all.

It seems probable to me that if there are more cut-through switches
deployed now than 10 years ago, that it would be due to ones bought
8-9 years ago that haven't been retired yet. It is my -belief- that
the percentage of cut-through switches is shrinking quickly.
I can't say, though, that I have chased any industry numbers.

It is my suspicion that outside of some possible mil or
niche industrial deployment, that buying a cut-through switch
these days would be about like trying to buy a hub these days --
barely being made, and manufacturers "creatively mis-stating"
properties because it's cheaper for them to quietly re-label a
mass-production device than to continue to produce small market
technology.


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"pocket-sized" wasn't one of the requirements, but "low-end"
was, along with "fast" (since speed was the reason given
for preferring not to use a router.)

There are too many small-run and rebranded switches to keep track
of, let alone to decently survey to know how well they work.

I make it a practice to recommend against *any* "low-end" unmanaged
switches in any situation in which "fast" is even a hint of
a requirement, as it is my experience that if one wants "fast"
then one needs to be able to probe packet error rates and
to be able to monitor the switch to investigate throughput
bottlenecks, whether caused by the switch quality or just
a function of the topology and traffic patterns.

To put it in other words, it is my belief that "fast" and "unmanaged"
are thoroughly incompatible.

That being the case, although I do know of some consumer-level
"name-brand" unmanaged layer-3 switches, I won't list any of them,
as I would have to recommend against using any of them.

Re: Low-end Layer 3 switch?


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I was asked the same question in a job intervew at a large datacom
equipment company, interestingly enough.

Philosophically there is no difference.  At the time "switches" were
first marketed (and I bought one of the first Alantec switches sold in
northern Illinois), routers typically had fewer, lower speed interfaces
but were capable of handling many input types (I won't even attempt
layers) - routers typically had a card for anything a telco could put
out, plus Ethernet, Token Ring, FDDI, Arcnet, etc.

Switches in contrast were usually Ethernet only (10 Mb), but they had
multiple ports (say 12, 24, or even !36!) and a backplane which could
route some significant fraction of the load created by (24 ports x 10
Mb).

Today, with switches having every feature under the sun and routers
available at Best Buy with 10 Gb backplanes, the distinction is fading
fast.

sPh


Re: Low-end Layer 3 switch?



Rick Jones wrote:
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My understanding of it is that layer 3/multilayer switching is doing
routing in hardware rather than software. Where frames/packets are
swtiched based on more than just the MAC address. Most I have used are
fast simple routers, they can't do stuff like NAT that we have come to
expect from routers.

They usually have a CPU running software to run routing protocols build
a routing table and load it into the ASIC's which do the swiching. But
the CPU never really sees the packets like in traditional routers.

Another term I've seen used in Layer 3 switching is wirespeed routing.
Its not untill you get into the highend cisco routers(read expensive)
that can handle a full 100mbit of data.  A 2600 serise for example
can't route much more than a few mbit yet they cost around the same
price as a low end multilayer switch which can do wirespeed.


Re: Low-end Layer 3 switch?


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Hey guys:  great trip down memory lane; thanks!

Now:  any rec'os on the question ;-)

sPh


Re: Low-end Layer 3 switch?


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Not from me. "very low-end" implies unmanaged, and I do not
recommend any unmanaged switches for environments in which "fast"
is important.

If you give up one of the properties, "very low-end", "layer 3",
or "fast", then there might be some recs for equipment that you
wouldn't take a sledge-hammer to... at least not the -first- day.

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