ipfw: Too many dynamic rules

Vlad Galu dudu at dudu.ro
Thu Sep 9 21:27:43 UTC 2010

2010/9/9 Marat N.Afanasyev <amarat at ksu.ru>:
> I wonder, are these dynamic rules really necessary? let's see, a client
> connects to your web-server and you immediately should create a new dynamic
> rule, therefore you participate in this DoS attack as well as attacker. ;)

With a stateless firewall, you help the attacker even more. Because
he's able to connect to your httpd/whatever daemon is listening
directly and he can easily fill up the descriptor table of that
process. Limiting the number of states/connections from the same host
prevents that. Sure, those states eat up RAM, but so do the
established connections. Having a slightly more aggressive state
expiry policy always helps. Sure, there are accf_http(9), accf_data(9)
and various forking workarounds, but they don't work unless your TCP
server is specifically designed to use them.

PF also allows you to tarpit malicious hosts based on how often they
try to reconnect - you can dynamically add them to a table which you
can refer to from ALTQ.

Good, fast & cheap. Pick any two.

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