IP address conflict#

Symptom: a device works, then doesn't, then works again. Or the Octave device itself drops off the network at random. Data has gaps.

Why it happens#

Two devices on the same network use the same IP address. Each time one of them talks, the switch and the other devices update which MAC address owns that IP. Traffic goes to one, then to the other.

Common causes: - a fixed IP was picked without checking it was free; - a replacement device kept the old device's IP, and the old one is still connected; - the DHCP server hands out an address that someone also configured as fixed.

Prevent it#

For a static eth0 address, Test on the Configuration page runs Proposed IP appears unused: an ARP request for the new address. Never Apply when that check fails.

For an additional address, or before giving a site device a new address, run Connectivity with ARPing to that address first. No reply means it's free.

Detect it#

1. Run Network Overview and note the MAC shown for the IP in Neighbors.
2. Repeat after a minute or two, or run Connectivity with ARPing. A different MAC for the same IP means a conflict.
3. Compare the MAC with the label on the expected device. The first half of a MAC identifies the manufacturer.

Fix#

• Re-address one of the two devices — usually the one that's not in the site documentation.
• For the Octave device: pick a free address (Scenario 2), Test, Apply.
• Ask the site to keep fixed addresses outside their DHCP range.