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I deal with many clients in warehousing and industrial applications who have IT staff or local consultants. Many of these sites are still using a 10/100 Megabit switching backbone... I've managed to get some clients to invest in networking as a part of larger, more visible initiatives; e.g. security, warehouse management or VoIP (thanks to PoE).

My question is really about how to arrange a group of 3+ standalone switches in a server room/closet. Assume these switches are of the web-managed Layer-2 full-gigabit category (HP ProCurve 1800-24G) and have no dedicated stacking interfaces. Assume a normal range of servers and one uplink to a Cisco ASA firewall for internet connectivity. Often times, I see switches like this simply daisy-chained.

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The reality of small-business IT... :( enter image description here

With only two switches, I'd set an LACP bond between units. Spanning tree, if supported. But what about three or more units?

In my own environments, I've had the luxury of using higher-quality stackable gear or just leveraging full chassis switches (Cisco 4507, HP 5400zl) because of the need for PoE or more complicated routing. But what the correct process for the situation described above?

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The right answer is to buy proper switches. Given in the past, I've bought a 10/100 Cisco 4000 series chassis switch for less than 200 bucks (equivalent).. – Tom O'Connor Jan 6 '14 at 13:25
I love a good chassis switch, but just to play devil's advocate: Those cheap Cisco 4000-series chassis switches are power sucking beasts and portable heaters, though. Its also very difficult to make the cabling clean with a chassis switch like you can w/ staggered patch panels, 1U switches, and Neatpatch ( cable management shelves. – Evan Anderson Jan 6 '14 at 20:54
@EvanAnderson Say WHAT?!?! (another room at the same facility) – ewwhite Jan 6 '14 at 21:03
@ewwhite - Oh, I'm not saying that a chassis can't be made to look good (and that one certainly does), but I've been totally won-over by Neatpatch. I don't have any pictures of stuff I've done handy, but a quick Google image search on "Neatpatch" will show you some very, very pretty pictures. (I shudder to think about what the cabling might look like on a Cisco Cat6513 loaded up with 48-port 10/100/1000 blades...) – Evan Anderson Jan 6 '14 at 21:11
@EvanAnderson I got that, too... Don't make me dig into my photo archive. Answer the question, though!! – ewwhite Jan 6 '14 at 21:17
up vote 15 down vote accepted

You're limited to daisy-chain if you don't have spanning tree, as redundant links without spanning tree will cause a loop. LACP doesn't really do anything here, in your case it would only used for switch-to-switch redundancy and throughput increase.

Mind that there is no point of using LACP unless switches in both ends understands the LACP protocol.

My suggestion is to get managed L2+ switches that supports basic features like STP. Since you're mentioning HP - we're having great success with the HP 2520 switches for edge PoE deployments. Dirt cheap and reliable. I'd probably get a bigger model for a SMB server closet.

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The switches in use may sometimes support STP. The ProCurve 1800-24G does now. I'm trying to step some sites up to better equipment where I can. But until now, I've leaned on just deploying chassis switches to not having to think about managing multiple non-stackable standalones. What is the cabling approach for 3+ non-stackables that DO support spanning-tree? – ewwhite Jan 6 '14 at 13:38
@ewwhite depends on how redundant you want it. You could connect every switch to every other switch and use STP priorities to decide what links stay up and what links are backup. – pauska Jan 6 '14 at 13:39
So you suggest a full-mesh? – ewwhite Jan 6 '14 at 13:49
Depends on how many switches and the traffic flow really. If we're talking about 3 switches i'd probably connect Switch A -> B, B -> C and C -> A (backup link), and configure STP to block the link between C and A. – pauska Jan 6 '14 at 13:52
+1 - I don't have enough to add to actually contribute an answer. Obviously, the tradeoff here is redundancy (and throughput bringing LAGs into) versus "wasting" ports. More often than not I've got one or more devices that have a single network interface, making one of the switches a SPoF anyway, so I just end up with a "star" around the SPoF switch. When I do actually want redundancy with 3 switches, though, I'll generally do a ring w/ 2 ports LAG'd between the switches, using 4 ports on each switch, just like pauska says. When I get to 4 or more switches I'll do a dual-star. – Evan Anderson Jan 6 '14 at 22:00

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