Posts Tagged DNS
Email Error: Invalid EHLO/HELO domain
Posted by Bloggylife in troubleshooting on May 27, 2009
Sending from my company email to another company email I got this error (link)
smtp; 550 5.5.0 Invalid EHLO/HELO domain
It’s because the other end mail server complies with SMTP standard (RCF 5321)
For our external email transfers, our spam filter handles it, that is Mail Transfer Agent (MTA). The problem was the FQDN configured didn’t publically resolve. Our MTA public IP didn’t have a Host A record on public DNS. It’s just natted to a public IP through our firewall.
You might wonder how this is possible?
See we receive through one SMTP connector (SMPTin.company.com) and send throughout another (SMTPout.company.com). So our DNS records, MX records, A records, are pointing to our (SMTPin.company.com)
So the HELO/EHLO value our mail server provided in the mail session when connected to the other end was not a publically resolvable FQDN. The value SMTPout.company.com, didn’t have an A record associated with it.
Updated the DNS records with the SMTPout.company.com A record.
I’m not sure how many mail servers out there comply with RFC5321 standard, but if you have this misconfiguration, you’ll face a problem when sending to such mail servers.
Thanks Nick for all the help you provided 
Network Tips – Hosts File
Posted by Bloggylife in windows on May 17, 2009
It’s easier to access by name than by IP. That’s what the DNS and WINS is for if you have them set in your network, but there are devices that are not registered and are only accessed by specific people.
Your switches, routers, firewalls, etc.
If you type in a name, it has to be resolved to an IP, before going to the DNS, your windows machine will check its hosts’s file, to see if it is listed there.
You’ll find your Hosts file in:
C:\WINDOWS\system32\drivers\etc
Open hosts file with notepad and enter information in the following format:
ip hostname
example:
10.10.10.2 Core1
To verify your settings, try pinging by name and you should see how the name is resolved.
I’ve been using this for a long time, I even copy my hosts file and pass it around for ease of access to other network admins.
Bind IP to DNS service
Posted by Bloggylife in troubleshooting, windows on May 16, 2009
We faced a problem with our DNS (link), that made me look deeper into its configuration.
Our server is Microsoft Server 2003 which runs two services FTP and DNS.
You can configure many IPs on a single network card, this is common with web servers running multiple sites. You can view the multiple IPs, in the Advance TCP/IP settings of your network card. Under the IP Settings tab.
For web services, in the IIS configuration you can assign each site an IP, because by default each site runs on the default port 80 (http), so if you want to run multiple sites on the same IP you need to assign different ports not used by other services. So to avoid all that and for end users to access directly through http default port, each site has an independent IP.
For DNS in Microsoft, if you go to the management console, there are some settings to which IP to listen to receive DNS requests and also, which DNS servers to trust to load records from. To know which IP the DNS is actually using, right click the DNS and select Launch nslookup, the IP that appears at the top of the command window is the IP binded to the DNS service.
What I came to notice, it’s the first IP in the IP addresses in the Advance TCP/IP settings.
Solution:
To overcome the problem, I faced in my previous post. I just removed the IP I wanted the DNS to use and added it again and it appeared on the top. And that solved the problem and I removed the IP used by the FTP from all our primary DNS settings.
In IIS settings, if you go to your FTP site, and see the properties, you’ll see the IP the FTP uses.
Email Problem: Fatal Error
Posted by Bloggylife in troubleshooting on May 12, 2009
Catchy title ;P A company contacted me regarding receiving a fatal error their email encounters when sending to our domain.
I saw the error message they are receiving, their email server, trying to resolve our domain using a local DNS in their premises and failing to do so.
This is how I troubleshooted:
- Checked our flow of emails, we are receiving and sending emails
- We have received emails from that company in the morning
- I nslookup-ed our email entries against our domain
- I used an external DNS and all our entries we resolving just fine
- I used external email account to send and receive emails with/without attachment (that took quite a while to reach its destination)
So I told them it’s a DNS problem, you’re having problem looking up our MX records in order to send us emails, check your DNS server.
Actually I was glad everything was fine from our end and left it at that and didn’t investigate thoroughly. The next day their IT person sends a report stating one of our DNS is giving them problems, so a temporarily solution, all DNS queries are forwarded to the functioning one!
WTF, I forgot to check the secondary DNS and what do you know, it’s not loading any records in any of the zones configured!!
So you see, they were having a problem, because their email server was querying our MX records against our secondary DNS server which had a problem. It wasn’t down or else it would’ve gone to the primary one, it was up and running with empty zones ;P
CONCLUSION, it was a DNS problem, but it was OURS not theirs ;P
Our secondary DNS is of course located in the DMZ, it’s running two services, DNS and FTP, each having their own IP. The issue was for security reasons, you configure your primary zone to allow zone transfers to listed IPs, I listed the seconday DNS IP but just to make sure you have configured the correct IP.
In DNS management console, right click the DNS server and select nslookup, the DNS IP should appear, that IP should be configured on the primary DNS.
Our problem, it was receiving DNS queries with one IP and loading zone information from primary DNS with the IP assigned for the FTP services!
I’m not quite sure why it’s doing that … I just included both IPs as trusted in the primary DNS configuration and voila it worked 
Sat down and wrote an apology email to the company and believe it or not when sending to their other company handling their IT services I got another error:
smtp; 550 5.5.0 Invalid EHLO/HELO domain.
What I did to solve this problem ;P used my gmail account to send the apology email to the IT person ;P I’ll just leave that to another day or as we all know tomorrow ;P
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