Basic info on DNS

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silverback
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Basic info on DNS

Post by silverback »

Some friends and I have recently had some problems with email which we think we've tracked down to problems with DNS servers. (Mail between us and anyone on the same ISP was getting through, but nothing was coming in from 'outside').
I've since Googled and found out some facts about DNS, but I'm left with a question which is "who looks after the DNS database?" - which is apparently loaded into every DNS.
Silverback

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HansV
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Re: Basic info on DNS

Post by HansV »

I have moved this thread from Scuttlebutt to the Networking and Wireless forum.
Regards,
Hans

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Argus
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Re: Basic info on DNS

Post by Argus »

How would that be? Since what is happening after your email server(s) is beyond your control.

Your mail client (software) > MTA (mail transfer agent) > MTA (mail transfer agent) > MDA (Mail delivery agent, "mail server") > recipient's mail client (software).

You would use DNS to find your server, beyond that nothing. You should ask your ISP/ESP (email service provider).
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StuartR
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Re: Basic info on DNS

Post by StuartR »

Each top level DNS domain has a different owner. So there is one owner for .COM, another for .NET, ORG etc. There are also country specific domains. These domain onwers manage the top level servers in their domain.

Every DNS name has an authoritative server, which is the place that definitively knows the facts about that domain. You can find out which DNS server is authoritative for a domain by typing the following commands in a Windows Command prompt.

Code: Select all

nslookup
> set query=ns
> eileenslounge.com (or whatever name you want to find out about)
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StuartR


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silverback
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Re: Basic info on DNS

Post by silverback »

I'm not understanding; here's how I thought things worked.
I thought that when I send an email to fredbloggs@somewhere.co.uk, this email address has to be turned into an IP address e.g. 138.68.175.3 to route it to its final destination. I further thought that this conversion of name to IP address was handled by a 'DNS database' which handles ALL the necessary conversions.
So, a) I don't know how things work or b) my OP question was "who is responsible for providing all the conversion data?" (called by me a DNS Database)
Is this not how things work?
Silverback
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StuartR
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Re: Basic info on DNS

Post by StuartR »

DNS is distributed, with each DNS server caching information for a period of time.

In a typical home scenario, your PC first checks its local cache to see if it already has a valid translation. It then asks your router (which includes a DNS server). If the router doesn't know then it will ask the DNS server at your ISP. If the ISP hasn't cached this translation then it will pass the request up to another DNS server. Eventually the request will go all the way to the top level server for the domain, which will return the name of the authoritative server. When the translation is found it will be cached at every level back down the treee of DNS servers. Each server will keep the translation in cache for a period of time specified by the authoritative server.
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Argus
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Re: Basic info on DNS

Post by Argus »

As Stuart said, and in the email world there is something called MX records, mail exchanger records, which tells which mail server is responsible for a certain domain. MX records is one of several DNS record types. Typically there are several MX records, for the same domain (to balance load etc.).

You can use NSLOOKUP with MX records:
set type=MX (or set q=MX)
Domain.abc

But this will not help you (or your friends).

As I metioned, what happens after you have sent a mail: it's accepted by a MSA (did not mention), mail submission agent (software), could also be the same as a mail transfer agent, MTA, it checks if the recipient is hosted locally, if not it's forwarded to another MTA. While doing this it will use MX records mentioned above. This is beyond your control.

https://en.wikipedia.org/wiki/Message_transfer_agent" onclick="window.open(this.href);return false;
https://en.wikipedia.org/wiki/MX_record" onclick="window.open(this.href);return false;
Etc.

What happens when you try to send to an address outside the domain of your email provider? Do you get a mail non-delivery report, such as "Undelivered Mail Returned to Sender"?
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silverback
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Re: Basic info on DNS

Post by silverback »

Stuart, Argus. Thank you both for these clear explanations. I'm particularly boggled that my router has a DNS server. Who knew?
Argus. All is working again now, but for interest, we did not get any non-delivery messages. The friend who started all this eventually got his missing two days' worth of email delivered between 0100 and 0300 yesterday.
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stuck
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Re: Basic info on DNS

Post by stuck »

silverback wrote:...eventually got his missing two days' worth of email delivered between 0100 and 0300 yesterday.
Which being translated means, the mail server at the recipient's ISP had 'an issue' so everything got held up until someone fixed the problem. Where upon a flood of backed up mail came gushing down the tubes and landed in the Inbox.

We had a variation on this at work a while ago. Our incoming mail slowly dried up. The IT people eventually found them, they'd got mixed up with the spam. Once they'd figured out why it was being held when it have shouldn't been blocked the flood gates opened and we got several hundred messages in the space of a couple of hours. Cue frantic headless chicken mode while we waded through them all to pick out the really really important ones that need our attention asap.

Ken

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silverback
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Re: Basic info on DNS

Post by silverback »

Ah. Those quaint times when I used to go to 'work'. :innocent:

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Re: Basic info on DNS

Post by LisaGreen »

LOL!!!

I initially read the last part of this as
which is apparently loaded into every DNS Silverback
I searched for quite a long time before I realised there is no such thing as a DNS Silverback!!!

Oops
Lisa