Ever wondered what the difference was between the ‘@’ symbol and the ‘*’ symbol when setting up a DNS Zone file for a domain name. In the past I have seen them used interchangeably with sometimes unexpected results.
The difference is that one (@) is for exact match search where there is no subdomain and the other (*) is a Wild Card – they are not interchangeable in all circumstances.
Consider the following Zone File for domain name xyz.com,
Any DNS request for an MX (mail) record for xyz.com (with no prefix) will return the two MX records mx1.mailserver.com and mx2.mailserver.com
Any DNS request for an MX (mail) record for the subdomain branch.xyz.com will return the two MX records mx3.mailserver.com and mx4.mailserver.com
If an A record request for the hostname ‘xyz.com’ is made, an exact match for this record with no subdomain is used (@) and it will return the IP address 126.96.36.199.
If an A record request for the hostname ‘www.xyz.com’ is made, an exact match for this subdomain is used and it will return the IP address 188.8.131.52
If an A record request for any other hostname e.g. ‘branch.xyz.com’ is made, the wildcard record (*) is used it will return the IP address 184.108.40.206.
In summary then;
The prefix ‘@’ refers to the domain name itself — it essentially means no prefix.
The prefix * is a wildcard — if a DNS request is made for an address that does not have a specific A record setup, then the wildcard IP address will be returned.
You hear it all the time: Monitor your logs. When there is a problem, check the logs. And it’s good advice, because system and application logs tell you anything you need to know, provided you actually look at them and understand what they are saying.
Viewing logfiles is merely a question of volition; understanding what they are telling you is a another kettle of clams entirely. Today we’ll look at what you might find in your network activity logs, and what it all means. Then you’ll know if you need to leap heroically into action, or if you can return to sipping your iced tea and catching up on your sadly-neglected napping.
The Mysterious — MARK — All newbie admins asks what this means in /var/log/messages:
Jul 1 16:04:53 windbag — MARK — Jul 1 16:24:53 windbag — MARK — Jul 1 16:44:53 windbag — MARK —
That’s just the syslog daemon letting you know that it is alive and well. You may set the interval to anything you like on Debian by editing /etc/init.d/sysklogd. This sets it to 60 minutes:
Then restart the syslog daemon:
# /etc/init.d/sysklogd restart
On Red Hat and derivatives, edit /etc/sysconfig/syslog :
Restart syslogd with service syslog restart. Then watch it happen in realtime on any Linux with tail -f /var/log/messages. (You can monitor the changes in any text file with tail.)