iptables block access to all ports except from a partial IP address

Question

I'm looking to block all ips from my server and it's ports with the exception of a partial ip 198.55..*. I'd like to limit access to an ISP region do to the fact my personal ip isn't static with our ISP. How would I go about this? Our server was compromised this evening and I'm trying to kill all other traffic to it. The code below seems to allow a specific ip, but does it block every other IP? Also if I use the x will that act like a wildcard? ``` iptables -A INPUT -s 74.231.64.xx -j ACCEPT ```

Accepted Answer

If you need to block all incomming traffic except an specific range, you should first change the default policy of the INPUT chain to DROP:

```
iptables --policy INPUT DROP
```

Then, you should give a netmask to `iptables` to allow many IP addresses altogether exceptionally. For example, if you need to only allow `74.231.64.1`, `74.231.64.2`, to `74.231.64.255`, you can use following command:

```
iptables -A INPUT -s 74.231.64.0/24 -j ACCEPT
```

`74.231.64.0/24` tells to iptables to apply the same role to all varying IPs between `74.231.64.1` to `74.231.64.255`. Similarly, you can widen this range by passing `74.231.0.0/16` or `74.0.0.0/8` instead.

IMPORTANT NOTE: Before applying this change, you better have a direct access to the system, not an over-network access. This is because a miss type may block you from the server.

iptables block access to all ports except from a partial IP address

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