Help me stop bothering the sysadmin

Delzhand

I've been a web developer for years, but I tend to get hung up on the sysadmin side of things - particularly DNS. I learn pretty quickly by doing things, but we don't have new clients often enough for me to get the kind of practice that really sticks.

The things that I tend to get stuck on are things that don't have an immediately measurable effect - like I changed a client's MX records to get them started using Google Apps for email, and I had no idea how long it would realistically take for mail to start being delivered there, or why he was able to send himself an email from his old AOL account almost immediately, but mail from my work account and personal Gmail account still hadn't shown up 5-10 minutes later.

My boss has been pretty patient with me, but I'd like to be able to do more without taking up his time, and maybe more importantly I'd like to be able to tell clients things more authoritatively. Are there any books H/A can recommend?

3lwap0

Keep in mind that local PC's have their own DNS cache - and that changing an MX record on the server may not have any impact on a client machine that doesn't need a DNS server to resolve an A/MX record it keeps locally. A flush of your clients local DNS cache would prompt them to contact a server and re-resolve whatever Hostname to IP.

Eventually, the local MX record will expire, and it will reach back out to the server to obtain a new record for the DNS resolver.

Truthfully, any OS or Vendor certifications are good DNS primers. A Network or Server+ book may be useful as well.

SeñorAmor

Typically, DNS records take 48 hours to propagate.

It can take less, but it should never take more.

Ruckus

48 hours worldwide. Most servers within your continent should be updated within 24 hours.

I'd recommend a Network+ book, or you can look for a community college evening/weekend course in Network Support or something similar.

bowen

Most are updated within 10 minutes.

tinwhiskers

The MX record is stored on tons and tons of servers, that resolve what IP address @domain.com get sent to.

When a server sends an email it looks up the domain name from one of these servers, and then sends the email out with the corresponding IP address.

So when you switched his email over from Tims@timstoys.com(hosted by AOL-do they do hosting?) to Tim@Timstoys.com(hosted by gmail).
You change the MX record at one location(your DNS provider), and that change is going to propagate to all the other DNS servers over time.

So as for the weird behavior there's a few different process at work here.

1) You haven't de-activated the AOL email server/account. The server process is still running.

2) mail sent from withing AOL is going to stay in side AOL. The old mail server isn't going to do a DNS look up on the domain its hosting. IF it was set up to host email for @timstoys.com, when it gets an email from one of those it just moves it locally. It never reaches the internet at large.

So if he's using outlook to send his emails, and it still has the account settings for AOL, it will look like he's sending and receiving messages. What is likely actually happening is: He writes an email and sends it to AOLs Servers; AOL never looks up what the DNS is because the server handling emails for @timstoys.com knows its own name; AOL sticks the email in his AOL inbox, which Outlook then pulls back down.


3) 3rd party emails will get routed depending on whichever DNS server they happen to use. So if some servers have the old address, and the others the new address, which ever one the senders mail server is using will dictate which inbox it goes to. Some will go to Google, others to AOL, in a day or so they will all go to Google.


#2 can be an absolute monster. We had an issue were someone kept an old email config in their outlook, and was actually sending mail out through the old server. When they tried to send inter-company email, it was getting routed to the old mail-boxes which most people had stopped outlook from checking, so they never saw it. But when it went outside the company, and the old server had to look up a DNS record, it worked fine.

Had similar problem with people who were still checking both servers, but sending emails from the old one to accounts that didn't exist when the old mail server was current. The server was saying not-deliverable, because NewGuy@name.com didn't exist on that server, even though he did on Google.