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New Member

Dns problem and cisco831


I have Cisco-831.

Few days ago was changed dns on isp side and as result i changed it on my cisco-831.

After that on lan computers(Lan computers use as dns ip address of internal interface on

cisco-831) that are behind cisco 831 started to be problems with opening internet sites. When on

lan computers dns was changed to real dns of isp,everything is fine. But we have many branches and

dns was changed on many of them from time to time,but such problems never happend.

Part of config about dns, if it not enough i will add full one.

ip domain name ************

ip name-server ***.***.***.***(real dns of isp)

ip dns server

ip dns spoofing

ip nat inside source route-map NONAT interface Ethernet1 overload

ip nat inside source static tcp ***.***.***.***1 22 interface Ethernet1 22

!route-map NONAT - is done for vpn channel.

Thanks a lot in advance for help! BTW ,sorry my english.


Re: Dns problem and cisco831

To resolve DNS issues, ensure DNS is working properly. If appropriate, test with an IP address instead of DNS name.

New Member

Re: Dns problem and cisco831

Thanks for your attention!

Sorry, i did not understand how to ensure DNS is working properly? DNS is on isp side. I have done some debugs of nat and saw that dns addresses are going through the nat. If i put dns ip address on client computers everything is fine and if it no dns ip address on computer it does not working,does not it mean that dns is fine?And sorry i did not understand what did you mean "test with an IP address instead of DNS name"

Thanks for your time!

Re: Dns problem and cisco831


One way to test DNS is first by checking that you are able to reach it. Then try performing nslookup.

From the MS-Dos CLI

C:\> ping isp_dns_ip_address

C:\> telnet isp_dns_ip_address 53

C:\> nslookup

> server isp_dns_ip_address


You should receive a non-authoritative response with IP address.