# DNS Resolution (Watch Mode)

In watch mode, Epimetheus can resolve IP addresses in label values to hostnames. This improves readability in Grafana and other tools that display label values.

## Default Behaviour

- The label **`ip`** is always resolved by default (when present).
- Resolution is done via reverse DNS. The result is used as the label value (e.g. `10.50.52.61` → `foo.example.lan`).
- Failed lookups leave the original IP unchanged.
- Results are cached in memory to avoid repeated DNS lookups.

## Additional Labels

To resolve other IP-carrying labels, use `-resolve-ip-labels` with a comma-separated list of label names:

```bash
./epimetheus -mode=watch \
    -file=network.csv \
    -metric-name=network \
    -resolve-ip-labels=source_ip,dest_ip
```

This resolves:

- `ip` (always, if present)
- `source_ip`
- `dest_ip`

Duplicate or empty entries (e.g. listing `ip` again) are ignored.

## Example

- **Input label:** `ip="10.50.52.61"`
- **After resolution:** `ip="foo.example.lan"` (if reverse DNS returns that name)
- **If resolution fails:** `ip="10.50.52.61"` (unchanged)

## When to Use

- CSV columns that contain IPs and are used as labels (e.g. `ip`, `host`, `source_ip`, `dest_ip`).
- When you want dashboards to show hostnames instead of raw IPs.

DNS resolution only applies in **watch mode**. Other modes do not use this feature. See [Operating Modes](modes.md) and [CLI Reference](../reference/cli.md) for full options.