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Switching vs. Ethernet Test Results - Understanding

Wed Sep 11, 2019 6:13 pm

Hi all,

I am a bit confused & lacking probably the knowledge when reading the Test-Results page for the CRS328-24P-4S+RM.
https://mikrotik.com/product/crs328_24p ... estresults

Is there somewhere a Guide/FAQ/WIKI where it is explained, what the differences are between Switching / Bridging / Routing and the given test results?
Personally I am interested in Data-Throughput and would like to know if the Switches can handle my required throughput or in which mode i need to operate them.
My use case would be mainly a LAN, with a Server and multiple CRS-Switches/Routers. With 1 Line connected to the Internet:
Image

If the server pushes data out via Fiber, assuming 5 Gbps and needs to serve several clients simultaneous (let's assume 150 Mbps / client), theoretically i could serve 33 clients (150x33=4.9Gbps) correct? Now my question is (related to the Test results), which of the shown figures are relevant in this case- is that Switching / Bridging / Routing? Or does it depend on how i operate the CRS (in SwOS or RouterOS?)

Thanks in advance for any input/feedback.
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mkx
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Re: Switching vs. Ethernet Test Results - Understanding

Wed Sep 11, 2019 7:51 pm

Switching is when CRS moves ethernet frames from one interface to another one by using it's switching hardware. It means quite basic stuff, athough CRS3xx can do many L2 stuff by using switching hardware. I your case that's all traffic between LAN hosts in the same IP subnet.

Bridging is similar to switching, but the more complicated tasks that can not be done by switching hardware. Not much qualifies as such on CRS3xx, on low-end devices that would be among other things interface bonding or even VLAN stuff.

Routing is when router moves IP packets between different IP networks (and might include NAT and firewall). In your case that's traffic between left and right LAN segments and traffic between both LANs and internet.
And, BTW, CRS is running SwOS can't route.

CRS family of devices is mainly switches and routing capacity is low. To asess real-life performance, I usually take the "Routing - 25 ip filter rules - 512 byte packets" and I don't take that figure for granted. For CRS328, the figure is 270Mbps, which is not something. If you want higher routing capacity (for the inter-LAN traffic), you'll have to look at some beefy router, e.g. CCR or RB1100AHx4 (the later has only got 1000Base-T interfaces). And beware that CCR devices are good at routing many connections in parallel. When it comes to single connection throughput, they don't exactly shine.
BR,
Metod
 
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Re: Switching vs. Ethernet Test Results - Understanding

Wed Sep 11, 2019 8:16 pm

Hi @mkx,

thank you for your feedback & explanation.
Just to make sure I understood you correct as well as applied to my use-case:
- Switching: Moving Ethernet Frames from one Interface to another, within the same IP subnet.
- Bridging: N/A in my case (no VLANs needed / active)
- Routing: IP packages moving between different IP networks (+NAT / Firewall)

I am just confused with this statement:
In your case that's traffic between left and right LAN segments and traffic between both LANs and internet.
For me the "blue" network is all within the same IP Subnet (192.168.88.xxx), so in my understanding (feel free to correct me) all traffic in there is "just" switched. Meaning, Data coming from the server, goes to the Switch(right) goes to the other Switch (left) and to a client connected there.
Routing in my understanding would be, if a client connected to either Switch (left or right), requests data from the ISP-Router (outside of the 192.168.88.xxx LAN). In this case the Switch on the left would need to route the traffic "outside"?
Or am I mixing this up, and any link between the left and the right Switch requires routing, even in the same IP subnet? :?
 
mkx
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Re: Switching vs. Ethernet Test Results - Understanding

Wed Sep 11, 2019 8:24 pm

For me the "blue" network is all within the same IP Subnet (192.168.88.xxx), so in my understanding (feel free to correct me) all traffic in there is "just" switched.
You're absolutely right, I've looked at the chart without due dilligence. So in your case, routing would only happen between LAN and internet. So CRS might do as router as well depending on WAN link speed.
BR,
Metod
 
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Re: Switching vs. Ethernet Test Results - Understanding

Wed Sep 11, 2019 8:35 pm

Great, thanks for the confirmation.
So basically, for the "blue" network I should be able to assume a rough max. throughput rate of 48Gbps (non-blocking Layer 2 throughput @ 64byte) for switching between the 2 switches. (Going back to my initially mentioned example, handling 33 clients with 5 Gbps should not be a problem?)
And as a connection to the outside world, without any additional restrictions for routing: 175Mbps as max routing capacity.

Is there any specific setting in RouterOS, that I would need to configure so that the Switches are set to "switching", meaning trying to push their throughput up, or is that handled automatically depending the Input / output IP-range?
 
mkx
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Re: Switching vs. Ethernet Test Results - Understanding

Wed Sep 11, 2019 8:42 pm

In ROS you first configure L2 stuff ... e.g. you create a bridge with selected interfaces as its members. "bridge" then offloads as much operations to the switching hardware and in your case that's just about everything related to intra-LAN traffic.

On the "routing" CRS you'll leave out one ether interface ftom the bridge and you'll use that port for WAN. Traffic will be handled by CPU.

Just a side note: one use case would be to partition switch to two independent halves. It this case the straight-forward approach would be to create two bridges and assign ether interfaces to one or the other. However, there's limitation that only single bridge can offload tasks to switching hardware. So one half of switch would be "bridging" with its speed limits.
The work around is to use single bridge with two VLANs, assigning ether ports as access ports to one or another VLAN. This setup is fully offloaded to switching hardware.
BR,
Metod

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