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Pix 501 - Allowing Routing of Public IP address

Posted on 2004-09-02
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Last Modified: 2013-11-16
Kind of an odd question:

I am currently participating in a thread i started at the cisco website. This is:

http://forums.cisco.com/eforum/servlet/NetProf?page=netprof&CommCmd=MB%3Fcmd%3Dpass_through%26location%3Doutline%40%5E1%40%40.1dd647db/0#selected_message

I will split the points between anyone who can add any useful, relevant information to help resovle the thread contained therein. You need not post back there if you are not registered - a reply here would do.

Many thank,
Daniel
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Question by:danielwatts
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by:Pete Long
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Hi Daniel

Im confused? do you have NO DNS on your LAN? if so why is s1 not querying your internal DNS its A record will return an internal address?


plus your comment

>>entered a line eg 64.1.2.34 s1.host.com

your host file is queried before the client tries to resolve DNS (after the internal cache has been searched)
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by:danielwatts
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In response:

No all of our DNS is hosted by a 3rd party. No DNS is running locally (except maybe a forwarder that just caches responses). Having internal DNS was an option but requires administration of the DNS thereafter. If we could fix the problem globally at the firewall it would be better.

The query order is set in nsswitch.
Currently mine is:
hosts:      files nisplus nis dns
so you are correct. /etc/hosts is queried before dns. This is how I am patching the problem for the moment!
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DNS doctoring (alias/dns) would work if the DNS response was forwarded through the firewall.  So using alias or the dns keyword on a static might not do the trick because it depends where the DNS server was/is.

To answer the main question; the pix will not forward traffic back out the same interface it heard it from.  This could open a hole in the firewall and thus compromise the security.  So the two answers that exist are to use DNS doctoring providing the DNS server responses go through the firewall or use two interfaces on the firewall.  Note that not even routers will NAT on the same interface.

--Tim
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by:danielwatts
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Guys thank you very much.

As it turns out the host must have just forgotten to clear xlate or something. The dns translation now works. Dig's to remote DNS servers now correctly return the translated internal IP address. Everything is dandy =)

The two interfaces on the firewall trick sounds clever - will remember that.
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ThanQ
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