This problem happens only with mtnl and a few times even on reboot, it did not open sites. I guess its their compatibility problem with linux. PPP is PPP whether it is linux or windows, hence question of mtnl compatible with linux doesnt arise. If there had been any compatibility issues then the connection would not have established during the 1st phase of connection i.e LCP.
This problem of getting logged on and not able to tranfer data used to happen with VSNL also, but it used to happen during daytime and never in the night for me. Did you notice the time when this problem occurs? Probably your connecting during heavy internet use hours (day time) and mtnl's bandwidht pool policy might not be in place?.
Meanwhile I am trying to figure out what is a caching-only name service as suggested by Kennith.
Caching-only name servers will not have any records of their own. When it recevied a request from a client for the first time it will query on behalf of a client to a nameserver. The next time client requests the caching server, it will answer from the date in its cache thus saving bandwidth and improving response.
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