Deny rules show source IP as sending RST, ACK instead of Firewall

[benson.low]

Hi CSC,

I have a question,

If ACL does not allow host to communicate, why is not the source IP be the firewall interface that deny the communication? This is detrimental as it does not reflect who is the root cause. Any way to reflect who is denying the traffic?

Rgrds,

Benson

[Patrick0711]

The firewall isn't designed to send resets when disallowing a host.  The firewall will silently drop the packet.  The idea being that you do not want to provide evidence that the host even exists if the connection is denied. 

A client may send a reset once the TCP retry count has been exceeded but the firewall shouldn't provide any indication that the traffic is denied. 

[benson.low]

Hi Patrick0711,

Thanks, but the problem I have is that even though I have enabled the ACL to allow comms, the message is RST-ACK to the client. It is the same message as I have deny the comms as well.

I have attached a screenshot of the communication flow using Wireshark, and included ASA Log captured to correlate the events.

My fear is that the firewall is the one that denying the traffic as the Reset-O stated that it is reset from Outside, does the message mean the outside interface reset the connections, or the host on the outside segment is resetting the segment.

TCP Reset-O

Reset was from the outside.