3.4 Adding MTA Resource Records to DNS

In order for your GroupWise system to receive messages from another GroupWise system via a dynamic Internet link, you need to create a DNS resource record for at least one of your MTAs. The resource record enables the MTA’s address, along with the Internet domain names associated with it, to be broadcast throughout the Internet.

You need to create the following resource records in DNS:

You can use your tool of choice to modify DNS. The following sections explain the information required and provide sample records.

3.4.1 Creating the Address ("A") Record

You can create an "A" record to map your MTA server’s fully-qualified host name to its IP address. Doing so enables you to use the server’s fully-qualified host name in the service ("SRV") or text ("TXT") record rather than the IP address. The "A" record is required if you plan to use a "SRV" record.

The following text shows sample "A" records.

; Address ("A") records
localhost       IN A
corp.serv.novl  IN A
gwdev.serv.novl IN A
gwsup.serv.novl IN A

Host Name (column 1): Use the host name assigned to the MTA’s server. In the above example, corp, gwdev, and gwsupport are the host names assigned to three MTA servers.

Class (column 2): Use IN to represent the Internet.

Type (column 3): Use A to specify an address record.

IP Address (column 4): Use the IP address assigned to the MTA’s server.

3.4.2 Creating the Service ("SRV") or Text ("TXT") Record

You can use either service records or text records to map your Internet domain names to MTAs. The following text shows sample "SRV" and "TXT" records:

; Service ("SRV") records
gwmtp.tcp.novell.com 172800 IN SRV 1 0 7100 corp.serv.novl
gwmtp.tcp.groupwise         IN SRV 1 1 7100 corp.serv.novl
gwmtp.tcp.groupwise         IN SRV 1 2 7100 gwdev.serv.novl
gwmtp.tcp.support 172800    IN SRV 1 0 7100 gwsup.serv.novl
gwmtp.tcp.support 172800    IN SRV 2 0 7100 corp.serv.novl
; Text ("TXT") records 
gwmtp.tcp.novell.com 172800 IN TXT "1 0 7100 corp.serv.novl"
gwmtp.tcp.groupwise         IN TXT "1 1 7100 corp.serv.novl"
gwmtp.tcp.groupwise         IN TXT "1 2 7100 gwdev.serv.novl"
gwmtp.tcp.support 172800    IN TXT "1 0 7100 gwsup.serv.novl"
gwmtp.tcp.support 172800    IN TXT "2 0 7100 corp.serv.novl"

Service.Protocol.Name (column 1): The service must be specified as gwmtp. The protocol must be specified as tcp. The name corresponds to the Internet domain name you want associated with the MTA. In the above sample, novell.com, groupwise.novell.com, and support.novell.com are the Internet domain names defined in GroupWise.

Time to Live (column 2): TTL (time to live) is the amount of time the record is cached in memory so it doesn’t need to be looked up again. TTL is specified in seconds. In the above sample, 172800 represents 2 days. If you don’t specify a TTL, the record is not cached.

Class (column 3): Enter IN to represent the Internet.

Type (column 4): Enter SRV to specify a service record. Enter TXT to specify a text record.

Priority (column 5): If an Internet domain name is associated with two different MTAs, the host with the lowest value is always contacted first. For example, a host with priority 1 is contacted before a host with priority 2. If two records with the same Internet domain name have the same priority, the weight number is used. In the above example, the two groupwise.novell.com records have the same priority, so the weight would be used.

Weight (column 6): The weight number specifies how to allocate connections among hosts with equal priorities. In the groupwise.novell.com record above, the corp.serv.novl host and the gwdev.serv.novl host have equal priorities, but the corp.serv.novl host has a weight of 1 and the gwdev.serv.novl host has a weight of 2. This means that 1 out of 3 times the corp.serv.novl host would be contacted first, and 2 out of 3 times, the gwdev.serv.novl host would be contacted first.

Port (column 7): The port number specifies the TCP port on which the MTA listens for incoming messages. The default port number for the MTA is 7100.

Host (column 8): The host specifies the fully-qualified host name or IP address of the MTA’s server. For a service record, you must specify the host name. For a text record, you can specify either the server’s host name or IP address. If you use a host name, it must be mapped to an IP address through an DNS "A" record. In the above example, corp.serv.novl, gwdev.serv.novl, and gwsup.serv.novl are all host names that are mapped to IP addresses through "A" records in DNS.