10G SFP Cards. How do they work when you daisy-chain connections?

dj_ripcord · February 2, 2021

Hi Everyone,

I am planning to slowly roll out a 10G network in my office starting with my NAS. I realize that I can purchase SFP cards with more than one port on them. As such, I am trying to figure out how the network is handled when they are used in a configuration where, for example: Switch ==> NAS ==> PC instead of Switch ==> NAS + PC. Reason I ask is because I am using that desktop Mikrotik 5 port switch and I am worried about running out of ports in the future when I upgrade other devices in my rack.

My planned config should look like this:

I am curious about this: For the connection to my PC from the NAS; does the PC receive an IP lease from the firewall? As though the SFP card in the NAS acts somewhat like a switch, and allows passthrough of packets intended for the PC?

Or does the Pc receive an IP through some kind of mini DHCP server on the SFP card? OR does the connection strictly work PTP, and there is no passthrough of the network connected to the other port?

These are the questions that make me wonder if this is even feasible as a 10G solution to connect multiple devices through essentially one switch port. If it works how I states initially, then all is peachy because then I can just use the 10G NIC in my PC as the main network connection - and therefore still have access to all devices on the network as if I was using my 1G NIC connected directly to my MDF switch.

Thanks for the help!

Eigenvektor · February 2, 2021

Normally all of your devices should be connected to the switch. They'd all receive IP addresses from the one DHCP on your network. Having more than one DHCP on the same network is a recipe for disaster.

If you connect it to the NAS instead, then you'd also have to configure NAT on the NAS, which means the NAS is then used as a router and is part of two networks, while your PC is on a separate network from the switch. In that case the NAS could have a DHCP for the second network. Not an ideal solution, really.

dj_ripcord · February 2, 2021

14 minutes ago, Eigenvektor said:

Normally all of your devices should be connected to the switch. They'd all receive IP addresses from the one DHCP on your network. Having more than one DHCP on the same network is a recipe for disaster.

If you connect it to the NAS instead, then you'd also have to configure NAT on the NAS, which means the NAS is then used as a router and is part of two networks, while your PC is on a separate network from the switch. In that case the NAS could have a DHCP for the second network. Not an ideal solution, really.

Well crap. That's exactly what I was afraid of. I was really hoping that a dual-port SFP card would just pass everything through. But I am definitely glad I asked before I went and bought one! Guess now I will be using all 4 SFP ports on that switch once I start this upgrade... smh.

Aragorn- · February 2, 2021

8 hours ago, Eigenvektor said:

If you connect it to the NAS instead, then you'd also have to configure NAT on the NAS, which means the NAS is then used as a router and is part of two networks, while your PC is on a separate network from the switch. In that case the NAS could have a DHCP for the second network. Not an ideal solution, really.

If the NAS supports bridging, he can simply bridge the two ports together and the NAS will effectively act like a switch for the traffic passing thru.

I have a CCTV server setup like this, it has a quadport NIC with the four ports bridged together, and each port connects out to a satellite switch with some cams attached. Its trivial to setup in Linux.