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On the information page for the above mentioned switch, it says
"Supports a maximum of 96 autosensing 10/100 ports or 96 autosensing 10/100/1000 ports or 16 mini-GBICs or 4 10-GbE ports, or a combination",
but the Switch fabric speed says 38.4 Gbps. If I am correct, it needs atleast 192 Gbps to switch 96 duplex non-blocking gbit ports.

  • First, is this correct and the mentioned 96 ports are complete nonsense?

  • Second, can I finally only use 19 ports without having traffic issues if there's alot of load on the network?

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1 Answer

up vote 3 down vote accepted

The ProCurve 4200vl series is a heavily-oversubscribed chassis switch. The 4204vl you're looking at is a 4-slot enclosure and has a lower switching capacity than the larger units.

The 96 Gigabit ports represent a maximum of four 24-port modules in the unit. You are correct in that the switching fabric speed of 38.4Gbps is less than the 192Gbps needed by 96 Gigabit ports running full-duplex...

The 38.4Gbps represents the hardware capacity of the unit, hence why only four 10GbE ports can be accommodated.

However, in reality, you're not going to be running all ports, all the time and at full-speed! If you are, you'd need a switch with a backplane that can support all ports at wire-speed (non-blocking).

The 4204vl is not designed for that.

In most situations, switches like this are used for a variety of devices, some of which may operate at 10Mbps or 100Mbps (printers, ILO/DRAC, phones, etc.), and others at 1Gbps (PC's, thin clients, servers). The goal here is consolidation.

What do you expect to be doing on your network? Typically, individual port utilization is far lower than a full 1000Mbps. That's how oversubscription works.

Fully-populated 4204vl chassis enter image description here

Typical port usage for my 4204vl setups in a branch office enter image description here

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Thanks for your answer! We are running some really traffic-intense applications so this doesn't look like the right switch for us. However, most switches I found have got non-blocking backplanes. What is the reason for having a small one, is it just a matter of production cost? –  Zulakis Oct 24 '12 at 14:33
    
@Zulakis It's convenience and having a central point to manage the switch. If you only need 96 ports, you can buy the ProCurve 4208vl, which has 8 module slots, but twice the bandwidth (76.8Gbps). That could be a better fit... or step up to the 5400zl series, like the small 5406zl, which can do 379.2Gbps... However, I'm pretty sure you could get by with a 4208vl switch. I don't worry about switching bandwidth unless I'm doing storage or having an intensive application like financial trading. –  ewwhite Oct 24 '12 at 14:39
    
@Zulakis "most switches I found have got non-blocking backplanes" <-- I don't think you're looking at modular switches then. Most modular switches are oversubscribed as the model in this Question. Stacking switches are usually similarly oversubscribed. Stand-alone switches commonly have full switching fabric. –  Chris S Oct 24 '12 at 16:04
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