using cisco router as DNS server

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Feb 5th, 2008
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We have set up our cisco router as DNS server. Its working file but we have a problem. Our inside interface is Public IP and outside interface is having Private IP of ISP network. We would like to know how to configure the router to run DNS server on a particular interface. So that all packets originating from the router have source Ip as public IP. any help would be greatly appreciated.


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Richard Burts Tue, 02/05/2008 - 21:23
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You ask the question as if it were a DNS issue. But as I read the question and try to understand what you are trying to accomplish it seems to me that what you need involves how to specify the source address on packets originated from the router. And that is not a DNS issue.

The good news is that IOS gives the ability to specify the source address for a number of applications. You can specify the source address for telnet, for ssh, for tftp, for ftp, for snmp traps, for tacacs, for radius, for ntp. In extended ping and extended traceroute there is an option to specify the source address.

Unfortunately there is not any single or simple way to do this globally. You must do it application by application.

If I have misunderstood some aspect your post could you please clarify for me.



yogeen_honnavar Wed, 02/06/2008 - 00:26
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ya, you are right i meant to ask how to specify source ip for packets originating from router.

and again you are right as u said we need to do it application by application. we found that the command

ip domain-lookup source-Ip

does solve our problem we are currently testing it. thanks for your reply.

yogeen_honnavar Wed, 02/06/2008 - 01:19
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On another system (X) in my LAN, I am configuring my router as DNS server. Hence, whenever any DNS query from system X reaches Router, the Router forwards it with its outside interface IP which is a private IP (provided by ISP).

How to configure Router that for such cases, source IP is my Public IP (inside interface)?


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