ip verify reverse-path & PIX best practices

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Mar 24th, 2007
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So I finally got my 506 up and running. I have internet access and inbound requests are being directed to the correct servers (smtp, http etc

I have noticed many have ip verify reverse-path enabled. Is this a function one would normally enable as a 'best practice?' If I do enable this, would I enable this on just the outside interface, inside interface or both since I have incoming requests to my servers? Any problems enabling this?

Any other recommendations for best practices?

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vitripat Sat, 03/24/2007 - 09:19
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Congrats on getting the PIX up .. :-)

The ip verify reverse-path command is a security feature that does a route lookup based on the source address. Usually, the route lookup is based on the destination address. This is why it is called reverse path forwarding. With this command enabled, packets are dropped if there is no route found for the packet or the route found does not match the interface on which the packet arrived.

Thus there wont be any success if we implement this command on the outside interface, because it will always find the route to the source using the default route.

By implementing this on other interface, we prevent ip spoofed traffic from leaving our PIX.

For more detail on this command, check out following link-


Hope that helps.




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