FiberBox Plus (CRS305-1G-4S+OUT)

The FiberBox Plus (product code CRS305-1G-4S+OUT) is a small switch built around fibre: four SFP+ ports at 10 Gbit and one gigabit copper port. It fits where fibre arrives and has to be spread out: a connection that has to continue to several buildings, the link between two premises on one site, or a small core where two servers and an uplink meet at 10 Gbit.

The catalogue lists it in the switches category with the default configuration switch. That has consequences for the roles the tool offers: router roles are blocked with the message "This is a switch". It runs RouterOS, not SwOS, so you do get an ordinary script.

The ports

• ether1: 1 Gbit copper. In practice usually your management port: this is where you plug a laptop in when you need to get at it, and where your management network arrives.
• sfp-sfpplus1 to sfp-sfpplus4: SFP+ ports at 10 Gbit. This is where the optical modules or DAC cables go.

The catalogue record lists no PoE-in and no PoE-out, so the PoE-out per port field does not appear for this model.

The configurator treats the SFP+ ports as ordinary wired ports: they go into the bridge, they can become access or trunk in the VLAN table, and they count towards the roles that require a number of ports. What the tool does not know is which module you put in. Whether a port does 10 Gbit, 1 Gbit or nothing depends on the optics and the far end, which no script can change. See Bridge and ports.

What is inside

From the catalogue: a 32-bit ARM processor, 256 MB of memory, a 98DX226S as the switch chip and a RouterOS licence of level 5. That switch chip is the most important part of this device: as long as traffic stays between ports in the same bridge, the chip does the work and the processor never sees it. That is why you may expect 10 Gbit from this switch and not from its processor. Level 5 is a generous licence; what the levels mean is in Licence levels and CHR.

What you have it do

The Switch role is what this device is for. The tool then puts every port in one bridge, builds a VLAN table with access and trunk ports, gives the device a management address, and writes no routing, no NAT and no DHCP server. The last port becomes a trunk by default, which on this model is the fourth SFP+.

The management address is the field to stop and think about. A switch without an address is a switch you cannot reach. The role sets a static address by default, which on a device like this is usually right: you do not want your core switch to change address because a DHCP server restarted. See LAN and DHCP for the field, and VLANs for which VLAN that address belongs on.

On MTU there is one thing worth considering at 10 Gbit: if you want jumbo frames, every link in the chain has to handle the same size. Half-configured jumbo frames produce faults that do not look like an MTU problem. See MTU and jumbo frames.

What it is good at, and where it runs out

Good at: moving frames from port to port at 10 Gbit, with VLANs, in a box you can put somewhere there is no rack.

Where it runs out:

• One copper port. Everything except that one port goes through a module. If you need four copper gigabit ports, this is the wrong device.
• It is not a router. The Home router, Office router with VLANs, VPN gateway and Wi-Fi roles are blocked with "This is a switch". Routing between VLANs is done by a router behind it.
• The processor is not a 10 Gbit processor. Everything the switch chip cannot do ends up on the processor, and there is no 10 Gbit to be had there.
• The catalogue does not know your modules. Speed, distance and wavelength of the optics are not recorded, and so are not in your script.

Which roles fit

• Switch: the normal choice. All ports in the bridge, a VLAN table, a management address, no routing.
• Core router (CCR / RB5009): it is offered, and it writes routed interfaces without a bridge, with OSPF or BGP and without NAT. On this device that is rarely what you want: it takes the traffic off the switch chip. See Static routes and policy routing and OSPF if you do want to go that way.
• Harden only (baseline): for a FiberBox that already runs and that you only want to lock down.

The quickest route to a working configuration

1. Pick One device and search for CRS305 or FiberBox.
2. Pick the Switch role.
3. Walk through the VLAN step: which port is access on which VLAN, which port is a trunk. Leave the list empty if you use no VLANs and switch the VLANs section off in advanced.
4. Set a static management address and an admin password.
5. Reset the device and paste the script. See Using the script.

If this switch sits in a larger whole, use Multiple devices in one site: the cabling then decides which ports become trunks, and the site checks look at whether your VLANs arrive everywhere. See also The network board.

What trips people up

• Locking yourself out. Putting the management address on a VLAN that does not arrive tagged on the port you are plugged into is the classic. Put your address on the VLAN that arrives over your uplink and check with /ip address print.
• A module that will not come up. If an SFP+ port stays down, look with /interface ethernet print and at the far end, not in your script. The configurator cannot influence the optics.
• Half-configured jumbo frames. One end at 9000 and the other at 1500 gives vague faults. See MTU and jumbo frames.