CRS304-4XG-IN

The CRS304-4XG-IN is a small switch with four 10 Gbit copper ports and one gigabit port. That is an unusual combination: 10 Gbit normally lives on fibre. Copper lets you use cabling that is already there, which suits a study with a NAS and a workstation, a wall cabinet, or a place where two servers need to sit close and fast.

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 through ether4: four 10 Gbit copper ports. This is what the device is for.
• ether5: one 1 Gbit port. In practice your management port: plug a laptop in and you can reach the switch even when something is wrong on the fast side.

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: in the Switch role nothing is routed. Which port becomes the trunk is chosen in the VLAN step; by default the role makes the last port, ether5, the trunk and the rest access ports. On this device you usually want the opposite: the gigabit port is your management port and your uplink belongs on a 10 Gbit port. So look at it. See VLANs and Bridge and ports.

At 10 Gbit the question of jumbo frames arrives quickly. See MTU; a higher MTU has to match on both ends of every cable.

What is inside

From the catalogue: ARM 64bit, 512 MB of memory, licence level 5 and the 98DX2528 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: at 10 Gbit you want traffic going through the switch chip, not the processor.

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 fast copper links together without laying fibre, in a cabinet with little room. For a NAS and a couple of workstations that is exactly enough; see Recipe: connecting a NAS.

Where it runs out:

• Four fast ports. One of them usually goes to your router, so three are left.
• No SFP. If fibre arrives you need a media converter or a different switch.
• No PoE. Anything that needs power needs an injector.
• Layer 2. In the Switch role nothing is routed; routing between VLANs happens on your router.
• Cabling. 10 Gbit over copper makes demands on the cable and the length. If you do not reach the speed, look there first; see Wired speed is lower than expected.

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, a static management address on the management VLAN, no DHCP server and no NAT.
• Harden only (baseline): for a switch that is already running.
• Core router: technically offered, but that role writes routed interfaces without a bridge. That is not what this device is meant for.

The quickest route to a working configuration

1. Pick One device and search for CRS304.
2. Pick the Switch role and walk through the wizard.
3. At the VLAN step, look carefully at which port becomes the trunk and change it if your uplink is on a 10 Gbit port.
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.

What trips people up

• Using the gigabit port as an uplink. ether5 is 1 Gbit. Your uplink belongs on a 10 Gbit port.
• Leaving the trunk where the role puts it. The default is the last port; on this model that is the slowest one.
• Setting jumbo frames on one side only. A higher MTU has to match on both ends; see MTU.
• Locking yourself out. After pasting, the switch is only reachable on the management address; see Switch unreachable.
• Old cabling. 10 Gbit over copper asks more of a cable than 1 Gbit does.