Networking basics for installers#
Five ideas explain almost every situation in this guide. Read this once; come back when a scenario uses a word you don't recognise.
1. IP address and subnet#
Every device has an IP address, for example 192.168.168.225. The prefix (or subnet mask) says which part of the address is the network and which part is the device.
192.168.168.225/24 means: the first 24 bits — 192.168.168 — are the network. Every device whose address starts with 192.168.168. is in the same subnet and can be reached directly.
| Prefix | Subnet mask | Addresses in the subnet | When you see it |
|---|---|---|---|
/24 | 255.255.255.0 | 254 | By far the most common on sites |
/16 | 255.255.0.0 | 65 534 | Large or lazy flat networks |
/23 | 255.255.254.0 | 510 | Sites that outgrew a /24 |
/28 | 255.255.255.240 | 14 | Small, carefully planned OT segments |
/32 | 255.255.255.255 | 1 — just this address | The RevPi's eth1, and host routes (Scenario 3) |
Tip
If someone gives you a subnet mask, convert it with the table. 255.255.255.0 is /24.
2. Same switch ≠ same subnet (Layer 2 vs Layer 3)#
- Layer 2 is the cable and switch: who is physically connected.
- Layer 3 is the IP subnet: who can talk directly.
Two devices on the same switch but in different subnets cannot talk to each other unless one of them also has an address in the other's subnet. That's exactly what Scenario 4 solves.
3. Gateway#
A gateway (router) forwards traffic to addresses outside your subnet. The default gateway is used for everything that has no better match — usually the internet.
Warning
A device has one default gateway, on eth0. The RevPi's eth1 never gets one — the device enforces this.
4. Routes and "most specific wins"#
The routing table decides which interface and gateway each packet uses. When several routes match a destination, Linux picks the most specific one — the route with the longest prefix:
Destination 192.168.1.60 matches… | Prefix | Wins? |
|---|---|---|
192.168.1.60/32 on eth1 (direct link route) | 32 | ✅ most specific |
192.168.1.0/24 on eth0 | 24 | |
0.0.0.0/0 default via 192.168.168.250 | 0 | only if nothing else matches |
This one rule is how the device keeps the right traffic on the right cable, even on messy sites.
5. DNS#
DNS turns names (like the Octave cloud address) into IP addresses. If the device reaches 1.1.1.1 but DNS Lookup fails for a name, DNS is the problem — see No cloud connection.
Site survey checklist#
Fill this in before opening the Configuration page. Most configuration mistakes come from a missing line here.
Site network (ETH0)
- Does the site use DHCP, or do you need a fixed IP?
- Fixed IP for the Octave device:
___.___.___.___ / __ - Default gateway:
___.___.___.___ - DNS server(s):
___.___.___.___ - Does the site firewall allow outbound internet for the device?
Every device Octave must read or control
| Device | IP address | Protocol / port | Same switch as ETH0, ETH1, or behind a router? | If behind a router: router IP |
|---|---|---|---|---|
| e.g. PV data manager | 192.168.1.17 | Modbus TCP / 502 | behind router | 192.168.168.250 |
Octave network (ETH1, RevPi only)
- IP address of every Octave device on
eth1— each needs a direct link route - RevPi secondary local IP (default
192.168.1.17) — not used by any Octave or site device - Does this subnet also appear anywhere on the site? If yes → Scenario 6