Cisco 4500X in VSS in Collapsed Core Model?

[devils_advocate]

Hello

We have 11x 3850 stacks (1-3 members per stack) to aggregate and I have been looking at the 4500X as the core/distribution switch in a VSS pair arrangement.

It seems the 16x 10GB model will provide enough ports for me to be able to do a 20GB port channel from each access layer stack, i.e one to each 4500X.

It will also allow me to create a 2GB port channel to the upstream Cisco router.

The previous design was to use 8x 3750X series switches as the core/distribution but I am not a fan of this as it has little resiliency and they are planning to run high def video streaming from multiple sources.

Is there anything I am missing as the cost of 2x 4500X seems to be reasonable and provides ample 10GB ports to aggregate with in a VSS pair?

We are using 3850s at the access layer so can aggregate cross stack members using PAGP.

Unfortunately the budget will not stretch to 2x 6500 or 4500E switches so this seems a suitable alternative.

Thanks

[Marvin Rhoads · Accepted solution]

Yes - I've done just that type of core for a couple of installations and it works just fine.

The 16-port model will be using up most of your available ports (11 ea. for the access layer, 2 ea. for the VSL and 1 ea for the router). I'd be more comfortable stretching for the 32-port model. However, you can add an 8-port expansion module later if you need.

[Joseph W. Doherty · Accepted solution]

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Posting

Is there anything I am missing as the cost of 2x 4500X seems to be reasonable and provides ample 10GB ports to aggregate with in a VSS pair?

The only thing you might be missing, with L3 switches at the edge, your collapsed core doesn't need to be VSS.  (VSS has many pros, but it does have a few cons too.)

If you didn't need VSS, other hardware is an option, for example, the older 4900M (NB: unless much less expensive, 4500X should be a better choice).

Unfortunately the budget will not stretch to 2x 6500 or 4500E switches so this seems a suitable alternative.

You've looked at (& priced) a pair of 4503s?  A 4503 with sup7 and a 4712-SFP+ would also meet your port needs, but would provide an additional full line card slot, not just a module slot.

[devils_advocate]

Hi Joseph

When I account for the amount of 10GB uplinks we need plus the VSL and the links to the Router and Call Manager Express router, looking at 2x 4503's seems to be more expensive.

I would need 2x Chassis, 2x PSU, 2x Supervisor, 2x 12 port SFP line cards.

This comes out to over 30k which is double the cost of 2x 4500x with the relevant PSU's.

Thanks

[Joseph W. Doherty]

Disclaimer

The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In   no event shall Author be liable for any damages whatsoever (including,   without limitation, damages for loss of use, data or profit) arising  out  of the use or inability to use the posting's information even if  Author  has been advised of the possibility of such damage.

Posting

This comes out to over 30k which is double the cost of 2x 4500x with the relevant PSU's.

I'm not surprised the 4500-X cost less.  If the extra 15K is too much, it's too much.

However, when making such decisions, you also need to not be "penny wise but pound foolish".  If you need to "grow" your core, you can a bit easier on the chassis, or even take the card components to a larger chassis.

What were you going to do with your servers?  If yours will use 10g connectors, especially "teamed", or you have a lot of busy ones with gig, their access switch's uplinks might become a bottleneck.  To avoid that, you might start to consider 40g uplinks (an upcoming option, I believe, on your 3850s) or you might directly connect to your collapsed core where you get the advantages of the core's interior fabric's bandwidth.

Don't misunderstand, a pair of 4500-X might be "your" best solution, but is it over the next 5 year?  Again, it may be, I wouldn't know; which is why I suggest you carefully consider your needs, and of course, within your budget.

I do agree a stack of eight 3750X wouldn't be a good solution.

[devils_advocate]

Thanks for taking the time to reply, its appreciated.

This design is for an upcoming client network and once handed over, we only do support on a pay by the hour basis so its not our network as such.

The previous design of 8x 3750x's for the core/dist layer was done before I started and the reason there are 8, was to accomodate 16x 10GB uplinks from the access layer. I suspect the 3750x stack will be a bottleneck though and will render the 20GB port channels from each access switch a little pointless if the core/dist can't switch or route at anywhere near the speeds if the uplinks started to become congested.

I have put my point across in terms of the design but budget comes into it and I think they may go with the 3750X design, even though this is a huge single point of failure and potential bottleneck.

Thanks for your help

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Unclear why you see the 3750X stack as a single point of failure, it is a stack.  The issue I would see would be downlink redundancy, as you only have 16 10g ports and you noted eleven access edge stacks and a router.

In theory, each 3750X pair of 10g ports should be able to operate at line rate.  The potential bottleneck might be the StackRing of 64 Gbps.  Although if just being used for the 16 10g ports, the oversubscription (5:1) isn't likely to be too excessive.

If the customer is willing to use 3850s on the edge, why didn't they consider them for the core too, as the 3850s support 4 10g per switch and there's much more ring bandwidth.  (Of course the 3850s are [currently] limited to a stack of 4, but they could provide the same number of 10g ports as a stack of 8 3750X.)

However, whether using 3750Xs or 3850s, both seem an expensive way to acquire 10g ports.  I.e. buy a whole switch to obtain 2 or 4 10g ports?  The 4500X (or 4503) pair (of single 4507R with dual everything, but chassis) appears to be better choice for core.

You might also reconsider whether all the edge stacks need to be 3850s.  Perhaps something in the new 2950X series, including the XRs, might be used for some edge stacks.  If so, what you might save there might be redirected toward the core.

[Leo Laohoo]

Talk to your Cisco account team and see if you can squeeze them for more discounts.

Also, are you doing an upgrade?  If this is an upgrade and old equipment will be thrown out, ask Cisco about the Technology Migration Program.