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Question about stacking and uplink bandwidth....

plesbit (IS/IT--Management)
20 Jan 11 6:11
This business used to be part of a big corporation who paid top dollar for top names in IT kit but a few years ago it was spun off on its own and has struggled ever since.  It's a pretty small set up now, with just 60 workstations and a few servers.  The network is a basic setup with a core switch and two edges and the equipment was once high spec but is now very old and in house expertise very limited.  No real money is available to throw at the issue but recently, after some problems at one end of the building I replaced a pair of very old HP ProCurve switches (one managed and one not) with a pair of Netgear FS728TS smart switches.

Each of the old HP switches had its own dedicated (10/100) uplink back to the core.  The new Netgear ones have two managed gigabit ports each and one of these has been used on each switch provide the uplink back to the core meaning each switch now has 10 times the bandwidth back to the core compared to before.

The problem I have is this.  These are stackable switches and the stacking works fine and so does the management interface when stacked.  But we do not seem to be able to have a separate uplink from each switch when stacked.  I had assumed, wrongly it would seem, that because the switches can detect the stack ports it would use them only for management purposes.  This does not seem to be the case.  Connecting the stack ports between the two switches whilst each switch has its own uplink to the core causes an immediate feedback loop which knocks out the entire network.

I seem to have two choices therefore.  One, I run each switch as a stand alone with its own IP and management interface and a dedicated uplink or, I stack the switches and combine the management into just one IP and interface but have all 48 ports using the single gigabit uplink on the stack master and therefore half the bandwidth available to the cabinet.

What I am doing wrong?  It seems self defeating to have stackable switches running as stand alone devices but it seems daft to half the available uplink bandwidth for the sake of easier management.  Surely there must be a way to combine the two - or is there something else that I have overlooked?
jimbopalmer (Programmer)
20 Jan 11 15:48
Your new switches support IEEE 802.3ad link aggregation (LACP).
If the core switch does as well, you can bond two physical ports to be one logical link, so you retain 2 gig throughput, but do not have loops as they act as one link.

With luck you may be able to do LACP using one port on each switch, but if not, both legs of the uplink will go to one switch, then the stacking cable will carry frames to the other switch.

I tried to remain child-like, all I acheived was childish.

VinceWhirlwind (TechnicalUser)
20 Jan 11 17:20
By the sounds of it, these Linksys switches are proper "stacking" switches, so link aggregation will hopefully work across both chassis, which is the ideal way of using it.
 
If your core switch is also Procurve they call link aggregation "Trunk", you can setup the aggregation ports either in the menu by going to "Sswitch configuration", "Port/Trunk Settings", then assign an identifying number against both uplink ports under "Group" and select either "Trunk" or "LACP" under "Type".
 
Also, you should definitely reduce your risk by enabling spanning-tree on the core switch (at least).
 
While you are at it, update the core switch firmware.
plesbit (IS/IT--Management)
21 Jan 11 8:48
Hi and thanks for the responses.  The new switches are Netgear FS728TS btw, not Linksys.  As I mentioned, we have very limited expertise in networking in house but the above responses appear to make sense even to me! smile

The core is a HP J4865A ProCurve Switch 4108GL but unfortunately at the moment, for reasons best known to the people that built this place, the SEG2 switches (the new Netgear ones) don't actually run directly into the core but actually into SEG1 (the other edge switch).  These are all unmanaged.  And before anyone has a fit about that, yes I know, it's just what I inherited from a previous regime and it is one thing on a very very long list of things I am now trying to sort out.  I expect it'll be at least another 2 months before I get a chance to rip out SEG1 and redo it so I guess I will just have to live with them not being stacked until then.

Again, thanks for the responses - it has been both a help and an education and in all likelihood I will be back with a new thread soon relating to exactly those changes to SEG1 and the core that I want to get done.

(I must confess though, I had a quick look inside the UI on the core and didn't see any indication it supports port trunking but will investigate in more detail when time allows)
VinceWhirlwind (TechnicalUser)
26 Jan 11 17:29
Yeah, you can setup "trunking" (LACP) on the 4108 just as I described above.

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