Best way to connect servers to 3Com switch stack

Posted on 2006-11-01
Last Modified: 2010-05-18

I am putting six 3Com 4200G 24port 10/100/1000 switches into a cusomters site in a few weeks.  They will be connected in a stack using gigabit stacking modules in the dual-personality port bays.  I understand they should be connected in a daisy chain with a link from the top of the stack to the bottom.

I guess my first question is what are the implications of having switches in a stack like this from a bandwidth point of view?  I mean you've got 24 devices on one switch but only one cable linking to the next switch.  And in a stack of six a packet may have to travel through up to two other switches before arriving at the destination switch.  Do the links not create a serious bottle neck?  If so, would there be a significant benefit to using say three 48 port switches in this case, so all switches are effectively 'adjacent'.  I'm just looking for some general information and observations on this point, it's a question I've had in my mind for quite a while.

The main question was abot connecting servers etc. to this stack, though I feel if the above question is answered I can answer this myself.  My thinking here is if the links between switches DO create a serious bottle next then maybe it would make sense to connect say server1 to switch1, server2 to switch2, server3 to switch3, InternetRouter1 to switch4.  That way one particular link isn't going to be saturated because it has all the servers and outbound routes on it.

Hopefully it's clear what I'm asking here.
Question by:Zenith63
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Accepted Solution

0xSaPx0 earned 400 total points
ID: 17850538
This is a common setup and I doubt you will saturate a gigabit link unless you have heavy bandwidth applications running on multiple nodes (streaming media, huge file copies, etc.) in which case 3come switches allow you to aggregate links, creating virtual links of multiple gigabit interfaces that are "bonded" so to say as one connection. So you setup 2 or 3 gigabit links as an aggregated link between switches, now you have a 2-3 gig trunk between them.

But that should not be necessary, however I would moreso suggest you consider purchasing a "core" switch, which will work at what is called the "core" layer, it will be a dedicated switch with all sub switches attaching to it. It is much faster and more efficient then daisy chaining "access" layer switches.

Core --> Distribution --> Access Layer

The Access layer is what you have now, you can skip the distribution layer and just install a core switch to attach the others to.

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Author Comment

ID: 17851046
We don't want to head into the 10s of thousands of euro range here, but what core switch would you have in mind?  Would the intention be to connect servers and gateways directly to the core switch as well?

Assuming we stick with the configuration I mentioned, is there any downside or benefit to connecting the servers to different switches in the stack?
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Expert Comment

ID: 17851303
Honestly, I would first see if you "need" to have a core layer. Are you a high volume network?, do you have tons and tons of traffic? (enough to saturate a full duplex Gigabit link at peak times) if the answer is yes or maybe, I would setup the network the way you planned and see if this is actually the case with the new switches.

Once you see how the switches are working and what the utilization is, you can plan for installing a core switch at your convenience, basically the core switch will be a 1 hour install (downtime) so its an easy install. As for which one, well I can give you advice but I really can't randomly pick one as I don't know you network =)

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Author Comment

ID: 17852133
OK fair enough, no I don't think it would be an overly high traffic network though it's not low either.

And on connecting the servers and gateways all to the same switch or distributing them?

Assisted Solution

cjtraman earned 100 total points
ID: 17856861
cascading (not stacking) the switches is meant mainly for management purpose and also to stop local traffic reaching the core switch. In the sense, you can avoid having multiple uplinks to core switches from access/distribution switches and to keep local traffic local by cascading. Instead of managing each switch, you stack to form a single unit and manage the switches like firmware upgradation, single IP assigment in one go. High port density switches are meant to circumvent space constraint in hub racks. Each switch maintain CAM table containing mac addresses and if the traffic is not intended, it will pass the traffic to next switch till the traffic reaches the correct destination. In case you have high volume traffic, then consider using matrix module switches for stacking as it provides higher backplane bandwidth.

Expert Comment

ID: 25871734
From 3Com Switch 4200G Family Configuration Guide:

The Switch 4200G series switches can form a stack only when connected through interfaces on 10 GE
stack boards

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