Defend that Perimeter | ISGMLUG

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Defend that Perimeter

If you’re responsible for the security of a network then you know it’s a full time job keeping it secure.   The important point is to ensure that you maintain a strong perimeter between you and the internet.  There are some rules and guidelines that most network professional enforce to keep their perimeter as safe as possible.

Block all Outgoing ICMP Errors

You should stop all these if possible as they’re used as reconnaissance on your network by a host of tools.  If you can’t block all of them for some reason then definitely block the host unreachable errors instead.

Use Proxies

You’ve got proxies on your firewall even if you don’t have a dedicated server.  Make sure you use proxies as an extra layer of defence between the internet and your hosts. If you enforce your own proxy servers and only allow those through the wall then you’ll ensure that proxy avoidance tools are harder to use.

Split DNS

Make sure that the DNS server that is accessible from the internet only has the bare minimum of entries.  Just your web server and mail server if possible, make sure you don’t let attackers download a full list of your internal hosts in a zone transfer!


Network address translation – if you can use internal private addresses makes your network much, much safer to attacks.

There are of course lots more things you can do however these are important.  Don’t just focus on your perimeter defense either, there’s pc firewalls, AV and content filters which can add extra layers of protection and make your network a much harder target.

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