Written 27 Aug 2026. This is a how-to, not a product card. Buy links are not tagged yet.

See how fast the leftover-box cable is talking

Before you buy a faster switch, check whether the leftover box is already at gigabit, or stuck at 100.

Link speed is how fast this cable is actually talking, in megabits per second. Ping can still work at 100. File copies crawl. You already plugged a cable in a cable beats Wi-Fi for the leftover box and reached the router in check that the leftover box can reach the house router. This note reads the speed on that plug.

Skip until SSH works

If you have never logged in from the couch, that is SSH from the couch. You can also type this at the leftover-box keyboard. Prefer this look after a cable is plugged in and ping to the router works: a cable beats Wi-Fi for the leftover box, then check that the leftover box can reach the house router. This note assumes you can log in from the couch, or sit at the leftover-box keyboard.

What this is

A look, not a shopping trip. 1000 is gigabit, the speed leftover laptops and OptiPlex boxes usually do. 100 is ten times slower: a bad cable, a cheap 100-only port, or an old laptop NIC. 2500 means a faster 2.5G port already. Do not buy a 2.5G switch for a leftover box that is talking at 100. Try another cable from the drawer first.

Find the cable name

SSH in from the couch, or sit at the leftover-box keyboard, then ask:

ip -br link

Skip the lo line. That is the leftover box talking to itself. Point at the ethernet line that is UP (often a name that starts with en, or eth0). Copy that name. Wi-Fi lines can wait if a cable is plugged in.

Ask for the speed

Replace NAME with the cable name you just copied:

cat /sys/class/net/NAME/speed

One number comes back. That number is megabits per second.

1000 is gigabit. Fine for a leftover box. File copies that still crawl are a later switch note: a faster switch for a first home lab.
100 is the slow trap. Swap the cable from the drawer, try another LAN port on the router, then ask again. Do not buy 2.5G for this.
2500 means this leftover box already has a faster port. You do not need a new switch for this leftover box.
-1, or the words Invalid argument, means that name is down. Pick the UP cable line from ip -br link.

Optional longer print

If ethtool is already installed, the same speed is on a Speed line:

ethtool NAME

Skip installing extra packages tonight. The cat look is enough.

What next

Write down the hardware address: see the leftover box's hardware address. Keep the number stable: keep the leftover box on the same number. Path to the router: check that the leftover box can reach the house router. Cable: a cable beats Wi-Fi for the leftover box.

Skip

Skip if SSH and the leftover-box keyboard both fail. That is is the leftover box still on? or SSH from the couch.
Skip a new switch for a leftover box stuck at 100. Try another cable first.
Skip buying Cat6 because Cat5 was in the drawer. The extra-fast ports can wait.
Skip forwarding port 22.
Skip buying a NAS for this look.
Skip Proxmox tonight. That is what a VM is, and when you do not need one.

Sources

Debian: ip-link. Linux: sysfs class net (speed). Official pages only. For the cable, see a cable beats Wi-Fi for the leftover box. For the path to the router, see check that the leftover box can reach the house router. For the hardware address, see see the leftover box's hardware address. For keeping the number, see keep the leftover box on the same number. For a later faster switch, see a faster switch for a first home lab.

Also on this topic

Check that the leftover box can reach the house routerBefore you blame the switch or buy a new cable, ping the router from the leftover box. A cable beats Wi-Fi for the leftover boxOnce the leftover box is doing real work, plug it into the router with a cable. House Wi-Fi can wait. Skip this if it is already on a cable. See the leftover box's hardware addressBefore you reserve the leftover box's number, write down the sticker-like address the router uses to recognize it. Keep the leftover box on the same numberSSH and Pi-hole keep working after a reboot when the router always gives the leftover box the same address.