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How to Create SRV DNS Records
A SRV record (Service Record) is a specification in the DNS system which defines the location of servers and services. SRV records are commonly used with many standardized communication protocols. An example of this is the Microsoft Exchange Autodiscover service.
In our example service, we will create a Microsoft Exchange Autodiscover Service Record. You will need the following information : Service Name, Protocol, Port Number and Host. In addition, we will need to define service Priority and Weight. Priority and weight are used to provision a service for high availability, load balancing and backup/failover service.
The priority field determines which record is used first. Clients use the record with the lowest-numbered priority value first, and attempt to connect to records of equal or higher value if the connection fails.
If a certain service has multiple SRV records with the same priority value, the weight field is used to determine which host to use. The weight value is taken into account only in relation to other weight values for the service, and only within the realm of records with the same priority value. Records with a higher weight are used first.
For our example, we will use :
Service Name : _autodiscover
Protocol : _tcp
Port Number : 443
Host : mail.domain.ca
In addition we will define the following values for priority and weight. For our example we don't have multiple records and thus will pick arbitrary values for those fields. We will differentiate the values only for the sake of clarity in the example service record definition. Please note you may not leave out the priority and weight fields, even if only one service record is present.
Priority : 10
Weight : 15
You will need to fill this information into the domainscanada.ca website in the following way :
Note: The trailing period at the end of the domain in the 'Address' field above is mandatory to prevent
||15 443 mail.domain.ca.
the system from appending the parent domain to the end of the address.
Please be aware that as with all DNS changes, it may take up to 24-48 hours for the modifications to propagate through the global internet's DNS system.
Checking the status of a SRV record
Using standard network administration utilities such as dig or nslookup, we can test the validity of SRV records.
$ dig _autodiscover._tcp.domain.ca SRV
$ nslookup -querytype=srv _autodiscover._tcp.domain.ca
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