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tesme33
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CRS312 link speed COMBO ports RJ45

Thu Feb 03, 2022 3:51 pm

Hi
im wondering what is the suported link speed of the RJ45 conntion part from the combo ports.

According to the block diagram it is the same chip as the 8 other ports and i can see that a DAC cable plugged in is advertising all speeds.

But what does this mean for the RJ45 part ?

Would this mean the RJ45 combo interface behave the same behaviour as the ports 1-8, except that you can only use them if no SFP+ is plugged in ?
combo_port.PNG
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mkx
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Re: CRS312 link speed COMBO ports RJ45

Thu Feb 03, 2022 8:13 pm

Block diagram explains the dilemma:

Image

When one plugs as SFP+ module, corresponding RJ45 port becomes inactive. Some devices sometimes need a reset to complete transition though.
 
tesme33
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Re: CRS312 link speed COMBO ports RJ45  [SOLVED]

Thu Feb 03, 2022 9:39 pm

Hi
thanks for your effort. Im aware of the diagram.
My question was more around the following text on the product page.
Details
10/100 Ethernet ports 	1
Number of Combo 10G Ethernet/ SFP+ ports 	4
Number of 1G/2.5G/5G/10G Ethernet ports 	8 
Which sounds like : The COMBO ports only support 10G. No differenciation if RJ45 or SFP+.

I have tried around a little bit and i can at least say
- you can configure them the same way as the other. And here in context of the speed advertisement.
- I was able to connect a 1G Ethernet USB-Stick
- 2.5G i gonna try tomorrow.


Which means for me for the COMBO Ports the following apply.

On RJ45 they support the same as the other 8 Ports.
On SFP+ I cannot say if 2.5 or 5 G are supported as i have no module to test.

Thx
 
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mkx
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Re: CRS312 link speed COMBO ports RJ45

Thu Feb 03, 2022 10:01 pm

I guess the description line would be too long if it read like this:
Number of Combo 1G/2.5G/5G/10G Ethernet / SFP/SFP+ ports 	4
And don't forget, those RJ45 ports quite likely support akso 10M/100M ...
 
tesme33
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Re: CRS312 link speed COMBO ports RJ45

Sat Feb 05, 2022 10:22 am

I guess the description line would be too long if it read like this:
Number of Combo 1G/2.5G/5G/10G Ethernet / SFP/SFP+ ports 	4
And don't forget, those RJ45 ports quite likely support akso 10M/100M ...
Hi
you are right. But it might be hard to get anything , except IOT devices, with a 10MBit port.

Thanks
Have a good day and stay healthy
 
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Re: CRS312 link speed COMBO ports RJ45

Sat Feb 05, 2022 11:06 am

... it might be hard to get anything , except IOT devices, with a 10MBit port.

Probably nothing uses 10Mbps these days now, the story about 100Mbps is different. My observation is that all devices capable of wake-on-lan put their ethernet ports to 100Mbps mode, the reason is very likely power consumption (lower bit rate means lower power consumption without exceptions). So any 1/2.5/5/10 Gbps RJ45 port effectively has to support 100Mbps or else there would be some loud shouting by clients who need such functionality.
 
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Re: CRS312 link speed COMBO ports RJ45

Sat Feb 05, 2022 4:47 pm

... it might be hard to get anything , except IOT devices, with a 10MBit port.

Probably nothing uses 10Mbps these days now, the story about 100Mbps is different. My observation is that all devices capable of wake-on-lan put their ethernet ports to 100Mbps mode, the reason is very likely power consumption (lower bit rate means lower power consumption without exceptions). So any 1/2.5/5/10 Gbps RJ45 port effectively has to support 100Mbps or else there would be some loud shouting by clients who need such functionality.
I agree. In addition, another reason for 100Mbps is the number of required wires. 8 wires are required for 1GbE, only 4 are required for 100Mbps. Since 100Mbps only uses half of the PHYs, it probably draws less power. AFAIK, 10Mbps draws even less power, but some faster NICs were dropping 10Mbps support for a while (earlier AQuantia NICs did not support it, at least on paper, while later ones do - looks like Marvell, after acquiring Aquantia, has deprecated Aquantia and Acqtion brands in favor of "Marvell Scalable mGig").
 
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Re: CRS312 link speed COMBO ports RJ45

Sat Feb 05, 2022 6:18 pm

Probably nothing uses 10Mbps these days now

At $DAYJOB we're still buying and installing a particular 10BASE-T device that's been in continuous production since the days when that was the "fast" speed, used by customers with the cash to upgrade beyond 10BASE2.

Why has it never been upgraded to faster Ethernet, you ask? Because it's a translator to even slower interfaces, RS-232 serial, remote-control IR, and human-pressed button contact closures. More speed would just let those interfaces get back to waiting for I/O faster.

The only reason it would be nice to make the Ethernet interface faster is that to do it, you'd have to make the CPU powerful enough to choke down all the noise you get on modern networks. (Broadcast storms, leaky multicast filtering, etc.)

Our most-used solution to that problem is to put it on the second network interface of the only server that needs to speak to it, creating a 2-node private LAN between them. The server then relays the information to/from the little 10BASE-T box, acting as a sort of Ethernet speed translator. The biggest problem with this option is that our preferred vendor's server motherboards have started to come with Ethernet ports that won't even speak 10BASE-T or 100BASE-T any more, so we can't use MDI-X; we have to add a switch to act as a media converter instead, even though it's only there to bridge two nodes. (And yes, it's an RB260GS lately.)

Our second-most used solution, when the 10BASE-T box can't be co-located with the server in the rack, is to put a hEX S in front of it to shield it from the rest of the network. It's configured as a firewall to keep the extraneous network noise from spamming the poor little box off the network.

And our third option is to convince site IT to configure their smart switches the same way as our canned hEX S configuration. Those of you who make a living as network engineers might think would be the best option, but it's always too much arm-twisting to get it done, so we've come to this pass. It's one of those "its faster to do it yourself than ask someone else to do it for you" things. Since our time isn't free, adding an RB260GS or a hEX S — depending on whether we need firewalling and intelligent traffic shaping or not — is cheaper all around.

any 1/2.5/5/10 Gbps RJ45 port effectively has to support 100Mbps

The gigabit-only ports on the servers I mention don't follow your logic because Ⓐ servers don't need WOL, being awake 24/7; and Ⓑ the energy use of the Ethernet ports is nothing when there's a honkin' Xeon processor on the other side of it. 😉
 
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Re: CRS312 link speed COMBO ports RJ45

Sat Feb 05, 2022 6:27 pm

Since 100Mbps only uses half of the PHYs, it probably draws less power.

Power draw isn't primarily a function of the number of wires. It's a function of the wire's capacitance and the signalling speed: it takes energy to force a capacitor to charge and then discharge, which is what you're doing when you send a digital pulse down the wire. Ethernet cables have surprising amounts of capacitance since even though they're pretty poor capacitor designs, when you put two conductors close to each other and run them for many meters, you can easily develop hundreds of picofarads.

The longer the cable, the more energy it takes to shove that parasitic capacitor through these state changes. The more state changes per second, the more energy it takes.

Ya canna change the laws o' physics, captin!
 
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mkx
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Re: CRS312 link speed COMBO ports RJ45

Sat Feb 05, 2022 8:38 pm

any 1/2.5/5/10 Gbps RJ45 port effectively has to support 100Mbps

The gigabit-only ports on the servers I mention don't follow your logic ...
Agree, servers are made not to be powered off. But there's even larger number of desktops and laptops. Many of them do get shut down or put to sleep while keeping parts of boards (including NICs) alive and awaiting those magical WoL packets. And many of them come with NIC ports faster than 1Gbps.

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