With GNU `grep` or any `grep` with `perl`-like regexp support, you can use the negative look-ahead operator:

```
grep -P '\b(?!192\.168\.)(\d{1,3})(\.(?1)){3}\b'
```

Or directly with `perl`:

```
perl -ne 'print if /\b(?!192\.168\.)(\d{1,3})(\.(?1)){3}\b/'
```

Those report the lines that contain a quad-decimal representation of an IP address other than those starting with `192.168.`, even if those lines also contain a `192.168.x.y` IP address.