CRS305-1G-4S+IN

The CRS305-1G-4S+IN is a small switch with four 10 Gbit SFP+ cages and one gigabit copper port. It fits on a shelf, in a cabinet, or behind a router with a 10 Gbit side. Typical places: a server corner with a NAS and two machines on fibre, a distribution point between two buildings, or the fast core of a small network.

The catalogue files it under switches with the default configuration switch, and the port layout is verified, so you will not see the "port layout not verified" note here.

The ports

• ether1: one 1 Gbit copper port. In practice your management port: plug a laptop in and you can reach the switch even when something is wrong with the fibre.
• sfp-sfpplus1 through sfp-sfpplus4: four 10 Gbit SFP+ cages. This is what the device is for.

There is no PoE-out: the catalogue records no feeding port, so the PoE-out per port field never appears. Anything that wants power over the cable needs an injector.

The catalogue records no WAN port, which is right for a switch. Which port becomes the trunk is chosen in the VLAN step; by default the Switch role makes the last port a trunk. Check that this matches where your uplink sits. See VLANs and Bridge and ports. With four identical cages the main question is which of them becomes your trunk.

If you want two cages to act as one link, that is bonding with LACP. And at 10 Gbit the question of jumbo frames arrives by itself; see MTU.

What is inside

From the catalogue: ARM 32bit, 512 MB of memory, licence level 5 and the 98DX3236 switch chip. Ample for what a switch does; the small-board warning never appears here.

hw_vlan is empty, so bridge VLAN filtering is the right route on this model and the note about losing hardware offload stays away. Leave the Hardware offloading (switch chip) toggle under Ports on.

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: bringing four 10 Gbit fibre links together in a cabinet with little room, with VLANs and a management address. For a NAS and two machines that is exactly the shape; see Recipe: connecting a NAS.

Where it runs out:

• Four cages. One of them is usually your uplink, so three are left.
• One copper port, at 1 Gbit. That is for management, not for work.
• No PoE.
• Layer 2. In the Switch role nothing is routed; your router does that. If you start putting an address on every VLAN here, you are building something the role does not write for you.
• Throughput figures. Our catalogue does not record them, so we do not quote them.

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. Every port in one bridge with RSTP, a VLAN table through /interface bridge vlan, a static management address on the management VLAN, no DHCP server, no NAT and no routing.
• Harden only (baseline): for a switch that is already running.
• Core router: technically offered, but that role writes routed interfaces without a bridge and does not suit this device.

The quickest route to a working configuration

1. Pick One device and search for CRS305.
2. Pick the Switch role and walk through the wizard.
3. Watch which cage becomes the trunk and which VLAN is your management VLAN.
4. Fill in the management address and the gateway; that address will be the only way to reach the switch.
5. Set an admin password, reset the device and paste the script. See Using the script.

If this switch sits between a router and a few access points, Multiple devices is faster: the cabling on the network board then decides which ports become trunks.

What trips people up

• Empty SFP+ cages. Without a matching module or DAC there is no link. Check with /interface ethernet print and see SFP port does not link.
• Using the copper port as an uplink. ether1 is 1 Gbit; your uplink belongs on a cage.
• Locking yourself out. After pasting, the switch is only reachable on the management address in the management VLAN; see Switch unreachable.
• The management VLAN untagged on an ordinary port. Send it tagged towards your router.
• Setting jumbo frames on one side only. Both ends of every cable, or it does not work.