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Vinay Sharma
Rising star
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This is the Q&A from "Troubleshooting ASA Firewalls - Packet Flow,Upgrade best practices and Handling dual ISP links" session.


Q:  In 8.3, is it possible to access the webserver from LAN(inside) using public IP?

A. Yes it is possible to do that. You will need to enable the option called DNS rewrite, that will enable you do access a server on inside using public ip.

PIX/ASA: Perform DNS Doctoring with the static Command and Two NAT Interfaces Configuration Example

DNS Server and Web Server on Mapped Interface, Web Server is Translated (Static NAT with DNS Modification)


Q. This is for dst nat. how about the traffic flow of src natting traffic flow?

A. Source address NAT is the 6th stage in the packet flow - just prior to the IPS redirection.


Q:  Differentiate NAT translate & NAT ip hdr, which separated by acl & inspection.

A. The first NAT stage translates the destination IP address of the packet and determines the egress interface of the packet. The second NAT stage is for translating the source IP address. 


Q:  What is the option for packet trace in FWSM?

A. That's a great question but unfortunately FWSMs do not support packet-tracer. We depend on the other tools (such as captures, and syslogs) to troubleshoot network problems. 


Q:  The order in which the packet will flow to the nat and I very confused with the new nat order.

A. That is completely understandable if you are new to this version of ASAs. Here are some documents that might help you understand this better:  There are some useful videos at the end of this doc. 


Q:  Is this capture command cpu intensive?

A. The capture command has very little overhead on the CPU. It is important though to ensure that you are as specific as possible when working with packet captures. 


Q:  What is the command to take backup via cli so that all  keys will backed up?

A. The CLI command to backup certificates using CLI is "crypto ca export <trustpoint_name> pkcs12 <secret_key>". 

More information about the command: 

If you are talking specifically about the AAA/VPN keys, you should use the command "more system:running-config".  


Q:  Can we execute Packet tracer command in FWSM firewall?

A. FWSMs do not support packet-tracer. You can use other tools like syslogs and captures. 


Q:  As the ASA an stateful so there is no need of opening ports in bir-direction . for ex: i have opened a port for a user from src to dst question is when the user try to  initiate the traffic from dst does that ACL works for me ?

A. As we discussed, the first stage of packet-processing is does the packet match an existing connection. hence, if the DST is responding to a previous packet from the SRC, then yes, the ASA will allow it without an ACL. 


Q:  How to look encrypted password in show run of asa?

A. One can not view the un-encrypted passwords of users using CLI. You can though, view the un-encrypted passwords for features like AAA or VPN using the "more system:running-config" and "show run all".  


Q:  SACK 0k is the only flag that is showin in packet capture?

A. That is actually a TCP option and not the TCP flag. Most of the supported TCP options will be shown in the packet captures. 


Q:  Please share the document for the packet capture

A:  here you go:


Related Information:

Video Recording

Session Presentation - Troubleshooting ASA Firewalls, Packet Flow,Upgrade best practices and Handling dual ISP links

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