Discussion:
Caching DNS
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Lieberman@Lieberware.com [blat]
2016-10-27 21:20:02 UTC
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My application on an AWS server has been successfully sending emails using BLAT for a long time.

Each of my users has a different email server (whatever they use for themselves separately from my application is what they use for my application).

Just one of my many users occasionally runs into an error. Their email server's tech support has asked me if I can have my program start using a "caching DNS."

Here's where I am naive. I don't know what this means, I don't know if I'm already using a caching DNS, and I don't know how to implement this.

Can you advise me?

Thank you... Art Lieberman
'Chip' chip.programmer@att.net [blat]
2016-10-28 04:04:29 UTC
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Post by ***@Lieberware.com [blat]
My application on an AWS server has been successfully sending emails using BLAT for a long time.
Each of my users has a different email server (whatever they use for themselves separately from my application is what they use for my application).
Just one of my many users occasionally runs into an error. Their email server's tech support has asked me if I can have my program start using a "caching DNS."
Here's where I am naive. I don't know what this means, I don't know if I'm already using a caching DNS, and I don't know how to implement this.
Can you advise me?
Thank you... Art Lieberman
DNS stands for Domain Name System, and the job of a DNS server is to translate textual names for computers into IP addresses that can be used for all Internet traffic. Internet Protocol (IP) is based entirely on numeric addresses assigned to every computing device connected to the Internet. To make life easier for us humans, computer were given names, and a system was developed whereby these names could be translated into IP addresses.

Normally, a person’s Internet Service Provider is responsible for identifying one or more DNS servers that can be used to provide this translation service. Company I.T. departments tend to provide a server for just this purpose, so they can limit the company network’s exposure to the outside world, and to block some sites deemed inappropriate for the company business.

As I understand it, your _application_ is not responsible for running and maintaining a DNS server. My guess is that your client’s I.T. department would prefer that your program be configured to use Amazon’s DNS servers rather than the client’s DNS servers. I don’t fully understand the reasoning for this. Is the client running your application directly on their computer, and thus running Blat behind the scenes on their computer, or is this all taking place directly on Amazon’s computers through a web browser interface? If your application is being interfaced through a web browser while being executed on Amazon computers, then the DNS queries will be handled by Amazon, not by your client’s I.T. department. If your application is being hosted by Amazon, but run directly on the client’s PC, then that client’s I.T. department is out of their collective minds.

Chip
Lieberman@Lieberware.com [blat]
2016-10-28 04:24:25 UTC
Permalink
Thank you, Chip. Here's more info...
My application is written in FoxPro and running in a Windows environment on AWS. Users connect via a Remote Desktop Connection. So, everything (including Blat) is running on Amazon's server; nothing is running on the user's computer. I think my client's IT dept is ok, but maybe we're wondering about the collective minds of the IT dept of the client's email server provider.


In my configuration, am I using Amazon's DNS server? Does it cache? And do I have any control over whether it is caching?
'Chip' chip.programmer@att.net [blat]
2016-10-28 15:43:09 UTC
Permalink
Post by ***@Lieberware.com [blat]
Thank you, Chip. Here's more info...
My application is written in FoxPro and running in a Windows environment on AWS. Users connect via a Remote Desktop Connection. So, everything (including Blat) is running on Amazon's server; nothing is running on the user's computer. I think my client's IT dept is ok, but maybe we're wondering about the collective minds of the IT dept of the client's email server provider.
In my configuration, am I using Amazon's DNS server? Does it cache? And do I have any control over whether it is caching?
Since your application and Blat are both running directly on Amazon’s computers, the name resolution is being handled by Amazon’s DNS servers. As an application running in Amazon’s cloud, you have no control over the DNS servers.

Chip
'Axel Skough' axel@skough.se [blat]
2016-10-28 05:24:14 UTC
Permalink
May this link help you?

DNS and BIND, 5th Edition


Help for System Administrators

* By: Cricket Liu, Paul Albitz
* Released: February 2009


Chapter 2. How Does DNS Work?
Caching



https://library.oreilly.com/book/9780596100575/dns-and-bind/25.xhtml

Kind regards,

Axel



Från: ***@yahoogroups.com [mailto:***@yahoogroups.com]
Skickat: den 27 oktober 2016 23:20
Till: ***@yahoogroups.com
Ämne: [blat] Caching DNS







My application on an AWS server has been successfully sending emails using BLAT for a long time.

Each of my users has a different email server (whatever they use for themselves separately from my application is what they use for my application).

Just one of my many users occasionally runs into an error. Their email server's tech support has asked me if I can have my program start using a "caching DNS."

Here's where I am naive. I don't know what this means, I don't know if I'm already using a caching DNS, and I don't know how to implement this.

Can you advise me?

Thank you... Art Lieberman
'Stuart Schaffert' stuart@it-techworks.com [blat]
2016-10-28 17:05:44 UTC
Permalink
What we really need at this point is an accurate definition of the problem.

DNS servers and clients do not refresh (effectively cache) a fetched DNS record until the TTL (time to live) for the record expires. The TTL is defined by the DNS administrator for the domain in question. If their server cannot handle the load then maybe they need to extend the TTL for their records. I think a "Caching DNS" violates the RFC for Domain Name Servers.

Stuart


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From: ***@Lieberware.com [blat]
To: ***@yahoogroups.com
Sent: Thursday, October 27, 2016 2:20 PM
Subject: [blat] Caching DNS







My application on an AWS server has been successfully sending emails using BLAT for a long time.

Each of my users has a different email server (whatever they use for themselves separately from my application is what they use for my application).

Just one of my many users occasionally runs into an error. Their email server's tech support has asked me if I can have my program start using a "caching DNS."

Here's where I am naive. I don't know what this means, I don't know if I'm already using a caching DNS, and I don't know how to implement this.

Can you advise me?

Thank you... Art Lieberman








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This email has been checked for viruses by Avast antivirus software.
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'Axel Skough' axel@skough.se [blat]
2016-10-28 19:42:43 UTC
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Ø What we really need at this point is an accurate definition of the problem.


Yes, I can strongly agree.



Ø DNS servers and clients do not refresh (effectively cache) a fetched DNS record until the TTL (time to live) for the record expires. The TTL is defined by the DNS administrator for the domain in question. If their server cannot handle the load then maybe they need to extend the TTL for their records. I think a "Caching DNS" violates the RFC for Domain Name Servers.



I don’t think one should refer RFC:s flr Domain Name Servers
 The traditional reference for the DNS is “DNS and BIND” by Cricket Liu and Paul Albitz <http://www.oreilly.com/pub/pr/1590> but maybe the Microsoft had some influence on the DNS in the past. I haven’t been so very close to the DNS evolvement in the last 10 years. But DNS is still fundamental for the Internet and the IPv4 as well as IPv6. However, I am retired since some years,

I can recommend the following readings regarding DNS:

Name Server: https://en.wikipedia.org/wiki/Name_server (Wikipedia)

Adding a Caching-Only DNS Server: https://technet.microsoft.com/en-us/library/cc794916%28v=ws.10%29.aspx (Microsoft Technet)

However, we need an accurate definition of the problem otherwise the discussion would be meaningless.



Från: ***@yahoogroups.com [mailto:***@yahoogroups.com]
Skickat: den 28 oktober 2016 19:06
Till: ***@yahoogroups.com
Ämne: Re: [blat] Caching DNS







What we really need at this point is an accurate definition of the problem.



DNS servers and clients do not refresh (effectively cache) a fetched DNS record until the TTL (time to live) for the record expires. The TTL is defined by the DNS administrator for the domain in question. If their server cannot handle the load then maybe they need to extend the TTL for their records. I think a "Caching DNS" violates the RFC for Domain Name Servers.



Stuart
Lieberman@Lieberware.com [blat]
2016-10-30 03:34:34 UTC
Permalink
"an accurate definition of the problem"

I'm working on getting that for us. Stay tuned...


Art
Lieberman@Lieberware.com [blat]
2016-11-03 20:10:21 UTC
Permalink
Ok, I was on the wrong track. The issue has nothing to do with DNS caching. I've submitted a separate query for my problem.


Thank you for your time. I'm sorry to have wasted it.
Art Lieberman
Lieberman@Lieberware.com [blat]
2016-11-05 03:32:19 UTC
Permalink
It turns out that AWS puts a limit on port 25.
Problem solved.

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