Benefits of layer 2/3 switching.

Hanpan

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Aug 17, 2000
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Could someone please explain what the benefits are of layer 2 switching over jsut a baseline switch and layer 3 over layer 2. I was looking at getting a managed switch but didn't see that much in the management options that seemed usefull. For anything usefull (ie bandwidth restriction) I need to get a layer 3 switch it seems and that is mega $$$.

Thank you in advance for the help.

One last little question. Why do so many switches have backplanes that are so damm tiny. I have seen switches with 2 gigabit uplink and 8 ports with 2.1Gbps backplane.

Just a fyi. We are not talking about 4 or 5 port SOHO switches here. While those switches are very good at thier price point and will do what you need them to do you will unfortunalty probably not find the talked about management options on them. On other hand you don't have to worry about administration or configeration of such options. A good way to check if you switch might have these options is too look for a console port (usually a serial port) on the switch. If there is such a port your switch jsut might be manageable. If not don't worry. YOur are not missing much unless you have at least 20+ pc's on a busy network.
 

Garion

Platinum Member
Apr 23, 2001
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"Layer 2" is just the geek-speek for a standard switch. It just looks at the MAC address of an Ethernet frame then forwards it out the appropriate port.

Layer 3 switches are more powerful - They function as routers AND as switches. A big network with hundreds of nodes can be broken up into smaller IP segments and still pass traffic between the switch ports at layer 2 switching speeds. Traditional routers have a lot of overhead and inherent issues for high-speed networks that a Layer 3 switch can overcome. It's also a lot cheaper to buy a device that can both route and switch than two separates, as well.

- G
 

sml

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Dec 26, 2001
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Layer 2 switching is fine for most installations; the benefits include MAC <-> port matching so you're not broadcasting traffic on all ports. you can do all kinds of neat stuff with managed switches - span a port, load balancing with etherchannel across a few different ports, etc. - you can also bind a certain MAC to a certain port, etc.
 

Hanpan

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Aug 17, 2000
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If layer 2 is jsut a regular switch then why are there managed switches and baseline switches?

It just seems to me that the management options offered by layer two aren't all that great.

 

spidey07

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Aug 4, 2000
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The management options offered by a layer2 switch are a god send and absolutely required if you run or manage a network.

1) unmanged switch = plug it in and see what happens

2) managed switch =
set spanning tree parameters so it'll play nice with all the other switches
RMON stats, so you can track utilization and error stats
set speed/duplex
SNMP poll so you know when it is down
upgradable software so you can fix bugs
VLANs
Quality of serfvice tagging and queuing features so you can run broadcast quality video/voice and still copy that 100 meg file
Logging
syslogging
traps
web based configuration for the networking challenged
trunking
managed, efficient multicast
TELNET, TELNET, TELNET - so you can troubleshoot that problem in Singapore.
Broadcast suppresion
Rate limiting
NTP - keep clocks in sync
graphical managmenet for the networking challenged.

more later.
 

Hanpan

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Aug 17, 2000
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Wow. I am glad I went for a layer 2 managed switch.

But what benefits would I see in layer 3 over layer 2?

btw i thought

Quality of serfvice tagging and queuing features so you can run broadcast quality video/voice and still copy that 100 meg file

and

rate limiting were layer 3 functions.

THanks for the response spidy et al...
 

spidey07

No Lifer
Aug 4, 2000
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Some advanced truely layer2 switches really do examie layer three but at the same time not really routing like a layer3 switch would. Hope this helps. A lot of the features I described come standard on cisco, nortel, extreme switches. I'm really not sure about the others.
 

Hanpan

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Aug 17, 2000
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Thanks for the help.

My new intel 460t should be here soon and then we'll see what it can do...
 

ScottMac

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Mar 19, 2001
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sml:
An L2 switch ( or just plain "switch") will indeed flood broadcast and multicast traffic out every port. More expensive (i.e.m "commercial grade" switches may have some broadcast/multicast control, but yer average, run-of-the-mill switch does forward broadcast/multicast traffic (out every port).

An L3 switch running in L3 modewill, by default, block broadcast/multicast traffic. Some L3 switches/routers have an IP helper function to forward broadcasts (by converting them to unicasts).

FWIW

Scott
 

Garion

Platinum Member
Apr 23, 2001
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I hate to say this, but I disagree with you on some counts Spidey..

A manageable switch is a layer 2 switch with some kind of management access built-in (via IP or serial port or whatever) that allows you to adjust whatever paramaters are available on the switch. For example, there's a lot of cheap manageable switches which don't support all (or even most) of the features you list.. Most 1st generation switches (Like the venerable 28115) were definitely manageable, but didn't do a whole lot, other than setting speed, duplex, and VLAN membership - Nothing fancy like a GUI or trunking.

The features of a switch are just that - Features offered by the manufacturer on the product. Management just allows you to go in and adjust how the switch functions beyond a simple "dumb" mode, where everything is set to Autonegotiate and one VLAN.

- G
 

spidey07

No Lifer
Aug 4, 2000
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Garion, very true. see my post above.

However - the 28115 did support trunking (remember it was a synoptics only kind of feature back then) and broadcast suppression.

and optivity for the networking challenged.
 

Garion

Platinum Member
Apr 23, 2001
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Oh, that's right - Their own proprietary flavor. Of course, that was before anyone ever even imagined 802.1q, so that's expected. Gawd, what a switch - I remember putting a couple of these in in '95, a few jobs back - Pretty hot stuff back then!

- G

 

spidey07

No Lifer
Aug 4, 2000
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yeah awesome switch in the day

16 ports of switched 10/100 for $15,000. My fourth switched ethernet installation. ahhhh...memories.
 

ScottMac

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Mar 19, 2001
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I think there was a problem with the 28115...something like...if you had standard spanning tree enabled on other devices in the network, and enabled some feature of the 28115, it locked everything up ....something with the BPDUs confused it...can't rememeber. I know we got alot of calls about it, and Bay was doing alot of dancing. It was a pretty hot item there for a while.

When you look back, it's amazing how far and how fast the technology has advanced. Then think about whay you'll be looking back to in five years from now.... "Oh yeah, THAT old POS....it was OK for the day...but even if folks had the right kind of power outlets in their home, no one would want a Cisco 8500...it's jusdt too slow and doesn't have enough ports....."

Wait 'till wireless DWDM hits the home market.....


FWIW

Scott
 

sml

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Dec 26, 2001
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ScottMac: that may be true for lower quality switches - my definition of a 'switch' is not some SMC 16 port POS, but a nice Cisco Catalyst or Extreme networks switch that I can totally manage, poll for stats via SNMP, set up syslog to log to another host, etc :)
 

spidey07

No Lifer
Aug 4, 2000
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scott,

yeah I remember that problem. It had to do with a special multicast address used for trunking, regular switches would pass the frame and the 28115s would think they were directly connected.

Happened to me before across some routers. The routers were also bridging (had to take care of netbios/OS2).
 

Hanpan

Diamond Member
Aug 17, 2000
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<< ScottMac: that may be true for lower quality switches - my definition of a 'switch' is not some SMC 16 port POS, but a nice Cisco Catalyst or Extreme networks switch that I can totally manage, poll for stats via SNMP, set up syslog to log to another host, etc :) >>



While I agree with you not everyone has 3k in their it budget for a switch.

At about 400 I felt the price was right for the intel 460t. Sure it's not a foundy or extreme networks swtich but it does offer some management without completely breaking the bank.

Oh and i heard many of the smc switches are made by HP.
 

spidey07

No Lifer
Aug 4, 2000
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if it is managed, go grab www.mrtg.org. give the switch an IP address, enable snmp with a community string and start polling all ports for utilization and errors. Now you'll know exactly what is going on your net.
 

ScottMac

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Mar 19, 2001
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Hanpan: In general conversation, if your say"switch" here, your talking to mostly folks with home/SOHO level switches. If you choose to define your own version of a standard definition, may it would be good to qualify it up front. That way you don't send dozens of people that don't know any better scurrying off to find the Broadcast/Multicast supression feature on their Linksys four-port.

FWIW

Scott
 

Hanpan

Diamond Member
Aug 17, 2000
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LOL>


My sincerest apology.

There are many very intelligent and helpful people in here and I wish to thank them for thier help.

It is true that we are not talking soho basic baseline switches here but I think that most people would ganger that from the talk about management options.


Small tip. If your switch has a console port (usually serial) chances are it is manageable and you can do some if not all of the things discussed. If no don't sweat it. YOu really don't need those features if you are connecting two computers to the internet.

If someone whould give me their opinion of the 460t it wold be greatly appreciated.

460t specs.

If you feel there is a better switch I should invest in I am open to suggestions.


And i will make it clear in the first post we are talking enterprise level switches here.
 

spidey07

No Lifer
Aug 4, 2000
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Hope I didn't go overboard. Just wanted to let you know what capabilities are out there besides plug it in.
 

Hanpan

Diamond Member
Aug 17, 2000
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Not at all. Only problem is now I want all these features but who will pay for the. I was aware of some of those features but always though they were only in the really highend expensive switches. Sadly i was rigth. :(
 

FFC

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Oct 23, 2001
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My .02 pence in simple terms.

A layer 2 switch forwards packets based on layer two address information.

A layer 3 switch is a router. It fowards packets based upon layer 3 addressing information. The term layer 3 switch is marketing &^%$%^
which was designed to make people think a box was faster because it was a switch not a router.

A managed device has an SNMP stack which will allow in most cases statistics to be extracted from the switch and configuration
of the switch via some form of remote management application.

Features available in a switch are nothing to do with it being a "managed" switch or not, they are just features you may or may not want. If you don't need them don't pay for them.