5 ms·

What's the advantage of doing this over plugging multiple gigabit adapters into a linux machine and adding them all to a bridge? I'm guessing performance might

What's the advantage of doing this over plugging multiple gigabit adapters into a linux machine and adding them all to a bridge? I'm guessing performance might be better with the hardware, but I don't know --has anyone done tests to show the difference?

MartijnBraam 2y ago
This is more efficient if most of the traffic will get switched, seperate adapters is more efficient if most of it needs to be routed.
simcop2387 2y ago
It'll be a combination of: 1. Throughput - say you use usb adapters, in a lot of ways usb is a shared bus so you'll run into max bandwidth quickly. This is especially because data will have to go in and then out, all the way to the cpu 2. Latency - because you're using software to do switching, it'll add time to process each packet and send it back out tne right place. You've also go any other interface latency adding to it 3. Power usage - eacj adapter will have it's own full network phy and hardware, which will increase the power draw. Combined with all the extra processing above and now your power usage is even higher. This means you also loae out on hardware offloading and other performance enhancememts that generally reduce power usage because less of the system is involved in mocing packets around 4. Features (potentially) - this will depend a lot on the hardware you choose, some of those cheap gigabit usb adapters i've tried didn't work with vlans and other features properly. But if you say load up a bunch of nice pcie cards with 1 or more ports thst support everything (never had issues with pcie ones) then you can now actually get a lot of features that are otherwise difficult or impossible on simpler hardware (though at that point you're doing routing more tham switching, but thay flexibility is why you'd potentially do this).
- Fnoord 2y ago
  We're only talking 1 gbit ethernet here, so you can have multiple of those ports on PCIe. I have a PCIe card here with two 2.5 gbit on it (don't remember exactly how much it was on Ali but between 20 and 40 EUR) and I can saturate both with iperf3. Since the example only uses 4 ports, it should be easy to make a simple router with just two PCIe cards. But there's probably 4x 1 gbit PCIe out there, too. And if you use 1 gbit fiber, that wouldn't cost much power nor would it need much speed. If your uplink is DSL, you could use a VigorNIC 132.
adrian_b 2y ago
For such a low speed and small number of ports using a hardware switch circuit is not necessary. Nevertheless, if the designing and building effort is neglected, I assume that the total cost of the hardware might be under $100, which is less than a computer with multiple interfaces would cost. Still, 1 Gb/s networks are rather obsolete. One could make a managed network switch that is bigger and faster by using only off-the-shelf components for slightly more than $200, e.g. a 6-port 2.5 Gb/s switch can be made with an Odroid H4+ having 2 ports, together with its add-on M.2 card with 4 extra Ethernet ports. Another variant is to use a small computer with an N100 CPU and 4 2.5 Gb/s ports, which can be bought in this price range from various Chinese companies. Similar small computers with 6 2.5 Gb/s ports are a little more expensive, perhaps slightly over $300.
- MartijnBraam 2y ago
  $100? I paid roughly $80 for two of these and the price per boards will rapidly converge to ~$17 when increasing quantity.
  - adrian_b 2y ago
    The PINE A64-LTS alone is $40 + shipping + taxes, so you cannot have a $17 total cost. I assume that you mean that the card with the switch circuit alone could reach $17, if made in a large quantity. However, you cannot make a managed switch with that card alone. If your current cost has been $40 for a card with the switch circuit, adding the PINE A64-LTS + whatever you have paid for shipping and taxes must make the total around $100, exactly like I have said.
    - MartijnBraam 2y ago
      I meant the cost of just the switch obviously... It can hook up to whatever Linux machine you have running and I happened to have this one in the drawer. The point of this was not to make the fastest or cheapest or most featureful switch available, it just had to fit in a case and none of the options have one port facing backwards so it doesn't require an ugly loop cable on the front of the final case. It's also possible to make a managed switch with that card alone, there is a footprint for a NOR flash chip, if you load the netgear GS105E firmware on that (which is available on the netgear website) then it will be just a GS105E without leds and one port on the back.
toast0 2y ago
As everyone else is saying, power usage should be less this way. Probably less latency to traverse the switch than a software bridge, too. Switching should continue to function if the host OS crashes, combined with a watchdog and recovery, you could have a more available system where maybe some things don't work for a brief interval, but much better than a software bridge (assuming the switch chip doesn't crash or get stuck, anyway). It depends on what your goals are though. If you want to inspect all traffic passing through the switch, having 4 interfaces is clearly better. If your host based switch is also doing a lot of communication, 4 interfaces gives you 4gbps from the hkst rather than 1gbps. Etc. Ex-enterprise quad 1G cards are $15 or less on ebay. I'm partial to silicom quad bypass 1g_ PEG4BPI-SD; the bypass feature can be fun, and they're cheaper cause they're weird (you can mostly configure them to be 'standard nics' once and then plug them into anything without much fuss, but getting there can be challenging. Early ones come with pci ids set to silicom as the vendor and subvendor which makes them harder to use; the -SD cards have intel vendor id and silicom subvendor, so the normal driver will attach. 4x10g ports would be more to manage, and you might not have enough throughput for software bridging, depending on the host system. And quad port 10g cards are harder to find. 2x10G is reasonably priced though, if you're patient.
denkmoon 2y ago
Your CPU will be in the data path there. Switches do their packet switching on ASIC rather than CPU. So it depends how good your CPU is, and generally that's not an effective use of whatever compute power you've got.

MartijnBraam 2y ago

This is more efficient if most of the traffic will get switched, seperate adapters is more efficient if most of it needs to be routed.

simcop2387 2y ago

It'll be a combination of: 1. Throughput - say you use usb adapters, in a lot of ways usb is a shared bus so you'll run into max bandwidth quickly. This is especially because data will have to go in and then out, all the way to the cpu 2. Latency - because you're using software to do switching, it'll add time to process each packet and send it back out tne right place. You've also go any other interface latency adding to it 3. Power usage - eacj adapter will have it's own full network phy and hardware, which will increase the power draw. Combined with all the extra processing above and now your power usage is even higher. This means you also loae out on hardware offloading and other performance enhancememts that generally reduce power usage because less of the system is involved in mocing packets around 4. Features (potentially) - this will depend a lot on the hardware you choose, some of those cheap gigabit usb adapters i've tried didn't work with vlans and other features properly. But if you say load up a bunch of nice pcie cards with 1 or more ports thst support everything (never had issues with pcie ones) then you can now actually get a lot of features that are otherwise difficult or impossible on simpler hardware (though at that point you're doing routing more tham switching, but thay flexibility is why you'd potentially do this).

Fnoord 2y ago
We're only talking 1 gbit ethernet here, so you can have multiple of those ports on PCIe. I have a PCIe card here with two 2.5 gbit on it (don't remember exactly how much it was on Ali but between 20 and 40 EUR) and I can saturate both with iperf3. Since the example only uses 4 ports, it should be easy to make a simple router with just two PCIe cards. But there's probably 4x 1 gbit PCIe out there, too. And if you use 1 gbit fiber, that wouldn't cost much power nor would it need much speed. If your uplink is DSL, you could use a VigorNIC 132.

adrian_b 2y ago

For such a low speed and small number of ports using a hardware switch circuit is not necessary. Nevertheless, if the designing and building effort is neglected, I assume that the total cost of the hardware might be under $100, which is less than a computer with multiple interfaces would cost. Still, 1 Gb/s networks are rather obsolete. One could make a managed network switch that is bigger and faster by using only off-the-shelf components for slightly more than $200, e.g. a 6-port 2.5 Gb/s switch can be made with an Odroid H4+ having 2 ports, together with its add-on M.2 card with 4 extra Ethernet ports. Another variant is to use a small computer with an N100 CPU and 4 2.5 Gb/s ports, which can be bought in this price range from various Chinese companies. Similar small computers with 6 2.5 Gb/s ports are a little more expensive, perhaps slightly over $300.

MartijnBraam 2y ago
$100? I paid roughly $80 for two of these and the price per boards will rapidly converge to ~$17 when increasing quantity.
- adrian_b 2y ago
  The PINE A64-LTS alone is $40 + shipping + taxes, so you cannot have a $17 total cost. I assume that you mean that the card with the switch circuit alone could reach $17, if made in a large quantity. However, you cannot make a managed switch with that card alone. If your current cost has been $40 for a card with the switch circuit, adding the PINE A64-LTS + whatever you have paid for shipping and taxes must make the total around $100, exactly like I have said.
  - MartijnBraam 2y ago
    I meant the cost of just the switch obviously... It can hook up to whatever Linux machine you have running and I happened to have this one in the drawer. The point of this was not to make the fastest or cheapest or most featureful switch available, it just had to fit in a case and none of the options have one port facing backwards so it doesn't require an ugly loop cable on the front of the final case. It's also possible to make a managed switch with that card alone, there is a footprint for a NOR flash chip, if you load the netgear GS105E firmware on that (which is available on the netgear website) then it will be just a GS105E without leds and one port on the back.

toast0 2y ago

As everyone else is saying, power usage should be less this way. Probably less latency to traverse the switch than a software bridge, too. Switching should continue to function if the host OS crashes, combined with a watchdog and recovery, you could have a more available system where maybe some things don't work for a brief interval, but much better than a software bridge (assuming the switch chip doesn't crash or get stuck, anyway). It depends on what your goals are though. If you want to inspect all traffic passing through the switch, having 4 interfaces is clearly better. If your host based switch is also doing a lot of communication, 4 interfaces gives you 4gbps from the hkst rather than 1gbps. Etc. Ex-enterprise quad 1G cards are $15 or less on ebay. I'm partial to silicom quad bypass 1g_ PEG4BPI-SD; the bypass feature can be fun, and they're cheaper cause they're weird (you can mostly configure them to be 'standard nics' once and then plug them into anything without much fuss, but getting there can be challenging. Early ones come with pci ids set to silicom as the vendor and subvendor which makes them harder to use; the -SD cards have intel vendor id and silicom subvendor, so the normal driver will attach. 4x10g ports would be more to manage, and you might not have enough throughput for software bridging, depending on the host system. And quad port 10g cards are harder to find. 2x10G is reasonably priced though, if you're patient.

denkmoon 2y ago

Your CPU will be in the data path there. Switches do their packet switching on ASIC rather than CPU. So it depends how good your CPU is, and generally that's not an effective use of whatever compute power you've got.