Re: DNS Forwarders Question

Graham J <graham@xxxxxxxxxxxxxxxx> wrote:

Tell us how you connect to the internet.

Assuming that you use a router, it will pick up the DNS details provided by
your (new) ISP.

Assuming your clients connect to the router and rely on the router's DHCP
service, they will all obtain the router's internal IP address for use as
their DNS server. So each client will ask the router to resolve names to IP
addresses, and the router will simply forward the request to the DNS server
provided by your ISP, which will probably have a cache. This in turn will
forward the request to other DNS servers when it deems its cache to be out
of date.

In general you should NOT use a fixed external DNS server, if run by your
ISP. If your ISP runs several such servers, they will want you to use only
those which are currently active, or those that they tell your router to
use, so that they can manage availability. Occasionally it may be necessary
to get your router to re-negotiate its connection with your ISP so that it
uses their currently active DNS servers. (I've found this to be
particularly true of BT.)

However, if you don't want to use your ISP's DNS servers you can tell your
router to use others. In which case, how do you know the servers are
available?

If you don't use a router the same general principles hold, but you should
explain more about your network so we can advise you properly.

It's a network with a pair of DNS servers. There's a Pix firewall
behind the BTNet router. LAN and WAN is through a router which is
inside the perimeter. The router for internet access (which is
changing) is connected to the firewall (which is not). So internal
clients use the internal DNS servers for name resolution and forwarders
send out to the internet somehow if a request isn't resolved internally.
So I can ping an external address from the inside and get a resolution
which comes from our DNS server, not the ISP's.

The default gateway is the LAN/WAN router.

Is that enough information?


Tim

--
Tim Gowen
.

Relevant Pages

  • Re: Discover Outgoing IP address
    ... > believe) can only mean that your ISP puts it's customers inside a "Network ... >> but my router reports the range.81.105.x.x range ... >>> It would most likely mean that your WAN address that the router sees is ... If your current dns servers don't support dynamic update, ...
    (microsoft.public.windows.server.sbs)
  • Re: Firewall for Static IP Addresses
    ... > internet line from our ISP - which they have nat'ed to 3 servers on ... > our internal network. ... > work if "our" side of the ISP's router was on a different network ...
    (comp.security.firewalls)
  • Re: CEICW Network Error
    ... I think Optimum (seen other posts about this ISP) does some strange things. ... While we can't possibly know the ins and outs of every ISP and router on ... IP address in a subnet that is different from the Internal LAN. ... Users brought in another tech and messed up internet ...
    (microsoft.public.windows.server.sbs)
  • Re: Remote destkop
    ... Lets not forget the original poster did *NOT* say if he was using a broadband ISP or a dialup ISP. ... router would automatically connect again. ... router would automatically register its new internet ... > reconnect after each disconnect, then automatically register its new IP ...
    (microsoft.public.windowsxp.work_remotely)
  • Re: How to change TTL of Linux
    ... A Windows machine will use an initial TTL of 128. ... RFC0791 (Internet Protocol) did not specify any value for this field. ... address from the ISP. ... presence of multiple machines behind a router. ...
    (comp.os.linux.networking)