Cisco 1811 with 2 ISP - DNS problem!

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Sep 25th, 2009
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I have 1811 with 2 ISP connection, both over fastEthernet ports. I did the 1 ISP route as primery and the seconf ISP as backup. The problem is that first ISP has DNS server 212.X.X.X and the second ISP has DNS 85.X.X.X. These are different ISP and every dns server works only with IP's from the same ISP.

Lets say that i have configured DNS servers like this:

ip name-server 212.X.X.X

ip name-server 85.X.X.X

Now if ISP1 goes down, ISP2 goes up and i have internet connection, but DNS server does not work, because router ask 212.X.X.X first that does not respond to IP of ISP2.

So how can i configure the Cisco to use second DNS server if uses ISP2 and first DNS server if it uses ISP1????

I hope i explained my problem in almost good manner :)

Pls help guys!

Thx in advance.

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Overall Rating: 4 (1 ratings)
paolo bevilacqua Fri, 09/25/2009 - 22:58
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Just use ISP-independent DNSs, like OpenDNS.

zenon_electronics Fri, 09/25/2009 - 23:02
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Hi, thanks for you fast answer.

Yes this is a solution, but i realy would like to use ISP specific DNS and i think there should be a way to resolve this issue?!

best regards,

Tihomir Yosifov

paolo bevilacqua Fri, 09/25/2009 - 23:04
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Recommend that in networking, you go for easy solutions, not complicating things unnecessarily.

Anyway, since router always source packets with the outgoing interface, configure ip dns server in the router and point he PCs to it.

zenon_electronics Fri, 09/25/2009 - 23:20
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Yes, i made it that way, but doesn't work.

the PCs DNS server is the router vlan interface and name servers are configured on the router. Anyway it needs something else to do it right.



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