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bypass external proxy due to NAT port 80 - outside int > forward to internal

Posted on 2013-11-27
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Last Modified: 2013-11-29
Hi. Hope someone can help me understand

Basically I have port forward on ASA firewall -   port 80 hitting outside interface - NAT to inside webserver.
It worked - I got hitcounts. However we have a "external cloud based cisco scansafe proxy"

the website did not load as the traffic was being forwarded out to the scansafe tower. An exception to bypass was put in and all is now working. website loads

I would like to understand why I needed the exception. If the traffic is coming in to the network - port 80. Why would it then go out to the scansafe tower for filtering. Its something to do with the NAT I guess - hopefully someone can explain in simple terms for me. Thanks
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Question by:philb19
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Henk van Achterberg earned 500 total points
ID: 39683016
I think you also filter tcp traffic with source port 80 (http). Can you share the scansafe config from the ASA?
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by:philb19
ID: 39683348
yes I guess thats the part i dont understand - why is the source port 80 - is it to do with nat? -the connection is source (outside) interface -> port 80 NAT to inside webserver - So im reading it as traffic IN to LAN - destination port 80
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Author Comment

by:philb19
ID: 39683366
the only thing i can pass on as to scansafe - it its a policy-map for http and https

I dont fully understand

"policy-map type inspect scansafe pmap-http" - same for https
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Author Closing Comment

by:philb19
ID: 39684837
dont know exactly IF its source port is 80 - however it is the case that "ALL" port 80 and 443 (IN any direction goes out to scansafe tower. - Its just the way it works, I just need to remember to do exceptions for these ports for anything IN-OUT through ASA
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Expert Comment

by:Henk van Achterberg
ID: 39684840
Great to hear it makes sense now :).

Good luck with your config!
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