📡 Monitoring an OLT with SNMP

ISPMan monitors OLTs (Optical Line Terminals) over SNMP. An OLT usually sits on the local network behind one of your managed routers. This guide shows how to add the OLT to ISPMan, allow ISPMan to reach it through that router, and enable SNMP on the OLT itself.

💡 OLT without SNMP? Tenda GPON OLTs (e.g. TES7001) have no SNMP agent — ISPMan monitors them through their web admin UI instead. Follow Monitoring a Tenda OLT.

⚠️ The community string, ports and NAT rules are generated per OLT. Always use the values shown on that OLT's page in ISPMan — never ones copied from another OLT or from this guide.

📋 Prerequisites

The router the OLT sits behind is added to ISPMan and online.
You know the OLT's local IP address (the address it has on the router's LAN, e.g. x.x.x.x).
You can log into the OLT's web or CLI to enable SNMP.

Step 1 — Add the OLT in ISPMan

Go to Devices → OLTs → Add OLT and fill in:

Parent router — the router the OLT is connected behind.
Name and Brand (e.g. V.SOL).
OLT LAN IP — the OLT's address on the router's local network.
OLT SNMP port — the port the OLT listens on for SNMP. Defaults to 161.
SNMP community — a memorable value is generated for you (e.g. shimmeringbrain). You'll configure the same value on the OLT. Use “Generate a new community” to change it.
Public IP (optional) — only if the OLT is directly reachable on a public address. Add :port if it's published on a non-standard port.

Step 2 — Allow ISPMan to reach the OLT

When the OLT sits behind a managed router, ISPMan needs the router to forward monitoring traffic to it. ISPMan pushes that rule to the router for you:

Open the OLT's page in ISPMan and click Router NAT.
Check the rule shown — UDP arriving on the router's WireGuard interface at the OLT's exposed port, forwarded to the OLT's LAN IP on its SNMP port.
Click Apply on <your router>.

Applying is safe to repeat — each rule is matched by its comment (olt-snmp:<olt id>), so it is never added twice. If the OLT has no parent router linked, the same dialog shows the RouterOS command to paste into the router's terminal instead.

Step 3 — Enable SNMP on the OLT

Log into the OLT's web/CLI and open the SNMP settings.
Enable SNMP v1/v2c and make sure the agent listens on the SNMP port you set in ISPMan (default 161).
Under the Community table, add a Read-Only community whose name exactly matches the ISPMan community (e.g. shimmeringbrain).
Permit SNMP access from ISPMan's monitoring subnet. Most OLTs have an access-control / firewall list that limits who may query SNMP. SNMP requests reach the OLT from ISPMan's monitoring server, which sits at the start of your router's WireGuard zone — so permit SNMP from the 10.x.0.0/24 of that zone, not from the router's own /24. For a router whose management IP (shown on the OLT's page in ISPMan) is 10.x.y.z, permit 10.x.0.0/24.

Example SNMP access rule on the OLT

Action	Type	Service	Source subnet
Permit	IPv4	SNMP	10.x.0.0/24

Keep the first two numbers of your router's management IP and end with .0.0/24: a router at 10.x.y.z means 10.x.0.0/24. Always read the management IP off the OLT's page in ISPMan — it differs per deployment.

⚠️ The community is a shared secret — it must be identical on ISPMan and the OLT. If you regenerate it in ISPMan, update the OLT too, or monitoring will stop working.

Step 4 — Verify

On the OLT's page, click Poll now.
On success you'll see system info, PON ports (with ONU counts), the ONU list, VLANs, and metric charts populate.
If it fails, the message tells you why — most often the community doesn't match, the NAT rule hasn't been applied (Router NAT → Apply), or SNMP isn't enabled/allowed on the OLT.

💡 Once verified, ISPMan keeps the OLT's dashboard and charts up to date automatically.