VSS and Maximum number of host Ports

Unanswered Question

I am exploring the VSS solution for our data centers. However, since we are

already esatblished the only driver for us is the ability to scale and

increase the amount of hosts we can conncet to a VSS cluster.

Our design takes:

Two data centers.

Two aggregation switches in each. The two pairs are connected with dark

fiber. So across the two data centers we have the same Vlans configured.

(Stretched VLANS) and MSTP instances.

In each Data center we have 1 Load balancer and 1 FW switch blades.

For the whole MST region we have Layer 2 connections between the


All our access switches (sup32) are thus redundantly connected to the local

aggregation switch.

Traffic outside of the MST VLANS is routed to the core - MPLS and MBGP.

This works very well. With a heavy reliance on STP - blocked paths


However as you see - we can sale to a maximum of 5040 ports/ hosts

7 blades (UTP/MM/SM 10/100/1000) * 48 ports * sup32 15 switches = 5040

7*48*15 = 5040

Every HoSt/Server in the DC LAN is redundantly connected upstream.

So the whole MST region - 2 datacenters- Layer 2 MST cloud has 10080 host

ports and half of them are in blocked state due to STP.

Therefore i cant scale beyond perhaps 15000 active/active ports in the

current design

To be scalable and cost effective VSS seems to help me in this. I could

scale to 40 - 50 K hosts ports that are also active.

Can someone help me understand whether my thinking is correct.

Thanks in advance

I have this problem too.
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Joseph W. Doherty Sun, 12/14/2008 - 05:47

It's not fully clear to me what your scaling limitition issue is. You describe seven 48 port line cards combined (which might be a 6509 with dual sups) but unclear how 15 sup32 switches are involved as a limit. What's the 15 limitation based on?

Assuming edge swithes used dual sup32-10GEs in a 6513 with eleven 48 port cards, that would provide 528 10/100/1000 edge ports per chassis. If you used two of the 10 gig uplinks, a 6509 with dual sup720s and using seven 16 port 10 gig cards, would support 112 10 gig ports, or about 56 edge switches. This then is about 29,568 edge ports off one aggregation switch.

Since you mentioned you're using STP and not Etherchannels, you could have two or more aggregation switches at either data center and increase your edge ports (similar to what you've done across the two data centers).

If you did use Etherchannel, then VSS would become important since Etherchannel is between the logical devices. I.e. VSS would allow you to double your port count when using Etherchannel. (NB: VSS has supported less service modules than non-VSS. You would need to check whether your FW and LB modules are supported.)


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