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Understanding Consumer Switch Performance

I would like to buy a new switch and I would like to understand what type of performance to expect…

When buying a pro-grade switch (the few times i have done it) I was able to find information about the back plane speed (cannot remember the correct terminology, sorry), but it doesnt seem that easy for consumer-grade switches.

I see a spec quoted often that seems to be my best hope is: Mpps

is that Mega packets per second? if so what exactly does that mean?

is it 1,000,000 packets per second or 2^20 packets maybe (1048576)?

also what is the packet size is it the frame size?

or am i dreaming thinking any consumer-grade switch will be honest/meet specs/ever perform.

Sorry for being a noob… just trying to find out what sort of performance I can actually expect from a switch. Some list bandwidth, but this number sometimes looks suspicious.

My use case is mutiple data sources and consumers on the same switch, i am happy with each being limited to 1Gbps but ideally i would like mutiple 1Gbps consumers and producers at the same time. I dont think i will be using this much bandwidth day-to-day but i specifically want to test performance for some other stupid pointless stuff i am doing.

I do have a pro-grade switch or two kicking about but they are helluva noisy and if some $20 thing of amazon will do i would rather use that.

As a side note i hope to upgrade to 1Gbps internet soonish so in theory just a NAS + internet could flood my LAN if the overall though-put is not there.

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I wouldn’t worry about the published specs … buy from a reputable vendor, and reputable brand name so you don’t get a counterfeit product.

For an ordinary gigabit switch, of any brand, the chips inside are going to get the job done, if it’s a $50 switch or a $500 switch. The extra features the $500 switch offers come from it’s management processor, and things like POE, as well as a better overall design like cooling, beefier power supply. Both the $50 and $500 switch will have the fabric capacity to handle all the ports talking at full speed.

Getting into exotic switches like 40, 50, 100+ gbit, then you run into fancier fabric and might need to research specs, but you’re also into five digit price tags at a minimum.

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I sort of thought this may be the case, as in its not that fast for modern chips to deal with in a way.

The bandwidth numbers i have seen are often twice every port running at max speed which made me suspicious, however considering the developments since gigabit first came on the scene maybe its not that surprising.

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A gigabit port needs two gigabits of bandwidth in full duplex operation, that might be why you’re seeing double numbers?

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Typically it’s all on a single switch chip, there’s no internal fabric between ports / backplanes etc… and so, you get L2 or L2+VLAN at wirespeed on all ports easily regardless of frame size. However, you should still check if the switches support 9k/16k/64k frames, just in case. 9k is usually fine, 64k usually won’t work, 16k might work.

(assuming you don’t hit the limit of unique mac addresses port port - for a certain type of popular atheros chip before they were bought by Qualcomm ~10years ago this limit was 4k unique entries).

L2+/L3 on consumer is where it gets interesting, the soc/chip vendors really don’t want their enterprise partner product lines canibalized by consumer gear in the SMB market - they limit what consumer gear OEMs are allowed to enable on different devices.

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Mpps is millions of packets per second. So if they just list Mpps, you have to do some maths… Basically, you do the following:

(((1000000000 x (PORT COUNT) x 2)/8)/(64 + 20))/1000000 = Mpps

So a 24 port gig switch would be:

(((1000000000 x 24 x 2)/8)/(64 + 20))/1000000 = ~71 Mpps

Basically, it’s all the ports (tx + rx) in Gbps divided by 8 to get GBps then divided by the smallest packet size (64 bytes + header) divided by 1 million to get it to Mpps.

When it comes down to it, for a gig switch, you probably want it to do around 3 Mpps per port, or as close to that as you can. That would mean it never drop a packet, even if you’re sending tiny packets at line rate. If you know you’re packets are always large, you can get a switch that is slower.

Packet and frame are the same things just in different contexts. You use the term packet when talking layer3 and above (it has an IP address) and you use frame when it’s layer2 (just talking mac addresses).

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