Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I'm trying to drop all packets from the internet that use a fake ip address so they appear to come locally.

Do I need both lines or only the first ?

--append INPUT ! --in-interface lo --source --jump DROP

--append INPUT ! --in-interface lo --destination --jump DROP
share|improve this question
You should consider setting /proc/sys/net/ipv4/conf/all/rp_filter. See here for a description. – ceving Jun 3 '11 at 17:56

You could use both, neither should exist really so blocking shouldn't hurt.

I'd also add rules for blocking non-routing IPs coming from outside your network.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.