DNS Configuration Issue / c851

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Nov 12th, 2008
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Trying to connect c851 router to Internet via AT&T DSL via PPPoE.

If PC connects to internet directly through DSL Modem [i.e. without router], no problem with email or any Windows client.

If PC connects through router, router assigns an IP address to PC, but it will not resolve domain names.

If I ping an external IP address, I receive a response, but if I ping the domain name of the same site (e.g. google.com), it does not respond.

AT&T says router must be configured to obtain DNS server address automatically but I cannot figure how to do that.

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Giuseppe Larosa Thu, 11/13/2008 - 00:47
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Hello Gregory,

have you got

ip address negotiated under interface dialer ?

Hope to help


rmcarthur Thu, 11/13/2008 - 00:55
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Hi Greg, there are a number of ways to achieve this.

To automatically do this then under the dialer interface use the "ppp ipcp dns request" command and the global "ip dns server" command.

In your dhcp pool use the "dns server A.B.C.D" where abcd is the lan address of your router.

This will cause the router to get the AT&T dns address and act as a proxy device. The first time a host requests the www.google.com address the router asks the AT&T dns to resolve it. The router then caches this entry locally and all subsequent request for that address are served by the router itself.

The other way, if you know the address, is to manually enter the AT&T dns address under the dhcp pool with "dns server a.b.c.d" as above.

Hope this helps


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