CRS312-4C+8XG-RM

The CRS312-4C+8XG-RM is a rack switch with twelve 10 Gbit ports: eight on copper and four combo ports that can be copper or fibre. Beside them sits one gigabit port. It belongs in a server cabinet where servers, storage and a router all want to sit at 10 Gbit, and where you want to keep the choice between copper and fibre open.

The catalogue files it under switches with the default configuration switch.

The port layout of this model is not verified in our catalogue. The tool therefore shows the "port layout not verified" note, and the script opens with a line saying the same. Run /interface print on the device and compare the names before you paste.

The ports

• ether1 through ether8: eight 10 Gbit copper ports.
• combo1 through combo4: four 10 Gbit combo ports. A combo port has a copper socket and a cage that exclude each other: you use one of the two.
• ether9: one 1 Gbit port. In practice your management port.

There is no PoE-out: the catalogue records no feeding port on this model, so the PoE-out per port field never appears.

The catalogue records no WAN port, which is right for a switch. The Switch role makes the last port a trunk by default, and here that is ether9, the gigabit port. That is almost never what you want: your uplink belongs on a 10 Gbit port. Change it in the VLAN step; see VLANs and Bridge and ports.

64 MB of memory on a 10 Gbit switch

The catalogue records 64 MB of memory for this model. That is exactly the line at which the configurator raises its small-board warning, and on a switch of this size it surprises people. The warning is right: keep the configuration small, do not install packages you are not using, and check what is left with /system resource print after pasting.

What that means in practice: this is a layer-2 device and it should stay one. No containers, no hotspot, no large firewall sets, no long rule lists. A VLAN table and a management address fit comfortably; a second life as a router does not.

What is inside

From the catalogue: MIPSBE, 64 MB of memory, licence level 5 and the 98DX8212 switch chip. hw_vlan is empty, so bridge VLAN filtering is the route we take on this model and the note about losing hardware offload stays away. Leave the Hardware offloading (switch chip) toggle under Ports on: across twelve 10 Gbit ports you want traffic going through the switch chip.

No radios and no modem, so no Wi-Fi package and no Wi-Fi generation in the catalogue entry.

What it is good at, and where it runs out

Good at: twelve fast links in one rack unit, with the freedom to pick copper or fibre per combo port. For a server cabinet that is the right shape; see LACP uplinks and MTU.

Where it runs out:

• 64 MB of memory. Keep it to switching.
• Unverified port names. Check them before you paste.
• Combo ports. Copper or fibre, not both at once.
• No PoE.
• Layer 2. Routing between VLANs happens on your router.

Which roles fit

Because the catalogue knows this model as a switch, the roles that route are greyed out with "This is a switch": Home router, Office router with VLANs, VPN gateway, Router + CAPsMAN and Hotspot. The Wi-Fi roles are greyed out with "No wifi radio", LTE / 5G router with "No LTE modem".

What is left:

• Switch: the role for this device.
• Harden only (baseline): for a switch that is already running, and the safest choice while you have not verified the port names.
• Core router: technically offered, but with 64 MB and no bridge that is not a good idea here.

The quickest route to a working configuration

1. Run /interface print on the device and write the port names down.
2. Pick One device and search for CRS312.
3. Pick the Switch role and walk through the wizard.
4. Put the trunk on the port where your uplink actually is, not on ether9.
5. Fill in the management address and the gateway; that address will be the only way to reach the switch.
6. Set an admin password, reset the device and paste the script. See Using the script.

What trips people up

• Leaving the default trunk alone. It sits on the gigabit port and turns your 10 Gbit switch into a bottleneck.
• Dismissing the memory warning. 64 MB on a switch this size really is the limit.
• Using a combo port twice. Copper and cage exclude each other.
• Not checking the port names. A script with the wrong names does nothing, or the wrong thing; see The script returns an error.
• Locking yourself out. See Switch unreachable.