On Fri, 28 Jul 2000, Chris Holt wrote:
> On 27-Jul-00, Fred Wright wrote:
> > On Mon, 17 Jul 2000, Chris Holt wrote:
>
> >> Have you tried making the DNS servers permanent entries? I am already
> >> required to do that, as the DNS servers that get "looked up" by Miami,
> >> are not correct for my ISP. (due to them using another provider for the
> >> POP in my area)
> >
> > It's preferable to use the automatic method when it works, since if the
> > ISP is doing their job right it means you'll automatically track any
> > changes they make to the DNS IPs. However, if they do it wrong then you
> > may need to make static entries and perhaps even disable the automatic
> > ones to get around it.
>
> I think I pointed this out before, but my ISP does not own the POP that is
> here. The DNS lookups work but the DNS servers that are returned do not
> belong to Earthlink. Everything works when I leave DNS on automatic, with
> the exception of sending mail. The SMTP server checks somehow, and does
> not consider me to be "dialed up" to earthlink, much as if I tried to use
> it from the LAN at work. I have seen several other services that use the
> same POP as earthlink, and they all prefix the logon somehow. For
> example, my earthlink logon is "ELN/digitalq". Now I'm assuming here that
> if the machine that is used there can tell I belong to earthlink, then it
> could somehow be told to spit back DNS servers that are owned by
> earthlink, but I don't know.
>
> Should I complain? I am, after all paying them for the service.
>
> I think that if they change the DNS IPs, it would be pretty obvious though.
> So I just call them up and find out the new ones, right?
It's not necessarily true that you need DNS servers associated with your
ISP. What you want is reliable servers "close" to your POP that give the
correct answers. Whether they should belong to your ISP or the party
that's supplying the POP depends on the architecture.
The SMTP server itself is completely unaware of your DNS settings, but I
can think of a few ways the DNS choice might come into play:
1) You're using a fully qualified domain name for the SMTP server, but the
different DNS servers are returning different IP addresses for it, and
hence you're actually using different servers. IP<->hostname mappings
aren't *supposed* to vary with the server, but various misconfigurations
are possible.
2) You're not using an FQDN, and the server name is being looked up in
different domains as a function of the DNS server chosen (perhaps due to
the "auto-add domain" feature), thus again yielding different IPs.
3) You're getting the same server each way, but your hostname is being set
up differently as a function of the DNS server, and the SMTP server is
being fussy about this.
You can check your lookups for 1 and 2 by using:
Miami:MiamiTCPDump -nvs 200 -i <interface> udp port 53
You can check your hostname with "Echo $HOSTNAME". You can check your
domains in the "Domains" database.
Fred Wright
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