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SRV Records

Service Records or SRV records are application specific DNS resource records used to locate a specific service. An example of this is the Microsoft Exchange server “autodiscover” record. This record is used to find and auto-configure a non-domain connected Outlook client. This resource record implements the underscore (“_”) as a method of namespace mangling; since this is normally an invalid DNS label, it helps keep the service DNS name unique and prevents conflicts with existing records. In short, this is a unique DNS label that is essentially a CNAME to the correct A record.

To configure an SRV record on an Ecessa device ensure that the namespace mangling character is omitted. Below is an example of the Ecessa device configuration for an SRV “autodiscover” record.

Service: _autodiscover
Protocol: _tcp
Port Number: 443
Host: mail.contoso.com

And here is the Ecessa configuration.

Again, notice the omission of the underscore (“_”), and the FQDN (Fully Qualified Domain Name) used in the Host Name column (trailing “.”). The other thing to note are the columns labeled Priority and Weight. These are SRV RR specific load balancing mechanism. This is a two level load balancing mechanism, with the Priority being the first qualifier, lowest being preferred and additional being failback records. The weight is relevant within the same Priority, essentially a sub-weighting of the Priority. As an example: Priority 10 Weight 5 would be used over the same SRV record with a Priority of 10 and a Weight of 6.

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