TCP Inspection

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Nov 5th, 2008
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I have OpenVPN set up to a remote site.

On the outward path traffic is directed through the VPN and straight in to the remote sites subent, however on the return path the traffic first hits the firewall before being re-routed back in to the subnet to the firewall (this was to avoid route statements on servers).

The problem with this is that the ASA denys TCP traffic on the return path as it did not see the original connection??

Deny TCP (no connection) Flags SYN ACK interface Inside

How do I either turn off this type of stateful inspection (not a great idea I know) or work around this?

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ajagadee Wed, 11/05/2008 - 04:58
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How about using the "Nailed" option under the static configuration.


(Optional) Allows TCP sessions for asymmetrically routed traffic. This option allows inbound traffic to traverse the security appliance without a corresponding outbound connection to establish the state. This command is used in conjunction with the failover timeout command. The failover timeout command specifies the amount of time after a system boots or becomes active that the nailed sessions are accepted. If not configured, the connections cannot be reestablished.

Note Adding the nailed option to the static command causes TCP state tracking and sequence checking to be skipped for the connection. Using the asr-group command to configure asymmetric routing support is more secure than using the static command with the nailed option and is the recommended method for configuring asymmetric routing support.



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