Recommendations for DNS

27 Jan 1998

      Greetings

A little late perhaps, but better late then never.
This is one of the actionspoints from RIPE-28, to present easy and short
recommendations for setting up a DNS.
I will be presenting this for the DNS WG on RIPE-29.
Any suggestions or remarks will be very welcomed.
Especially the times for the SOA records.

                              DNS recommendations.

By:

Hans Niklasson <hasse@swip.net>
Amar Andersson <amar@telia.net>

Scope: 

This documents act as a recommendation for configuring your DNS. This is
NOT a requirement, only a recommendation of things to think about when
setting up your DNS.

Purpose:

To decrease lame delegations and limit unecessary traffic due to resolving
problems, among other things.

Records:
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SOA      The address in this field must be a valid e-mail address to the
         administrator for the DNS.

Ex:

domain.xx.        3600    SOA     dns.domain.xx admin.domain.xx. 

SERIAL   Serial number should follow this format: YYYYMMDDXX 
         ( year.year.year.year.month.month.day.day.nr.nr ),
         where XX is the number of the latest update of the zone in the 
         same day.

Ex:

                  1998010101      ; serial

TTL      A good balance of this will reduce unecessary traffic between
	nameservers.

Ex:

                  28800   ; refresh (8 hours)
                  7200    ; retry (2 hour)
                  604800  ; expire (7 days)
                  86400 )  ; minimum (1 day)

MX       When pointing a domain to a mailserver/hostname, don´t forget to
         add a glue record ( A ) for this.

Ex:

domain.xx.        86400    MX      10 mail.domain.xx.

mail.domain.xx    86400    A       192.168.0.1

CNAME    Use this with percausion. It is *not* recommended to use a CNAME
         for a mailservers hostname, as this can cause resolving problems
         and mailloops.

A        A gluerecord can only point to an IP address.

PTR      This is used for reverse lookup of the IP address to a hostname
         within the zone. Make sure that your PTR records and A records
         match. For each A record there has to be a PTR record, and vice
         versa.

More tips:

Unecessary glue data:  

	Don´t add unecessary glue data about hosts that is not within the
	zone. This can cause resolving problems if the host changes IP
	address.

Ex:

domain.xx.        86400    MX      10 mail.server.xx.

mail.server.xx    86400    A       192.168.0.1

Trailing dots: 
	Don´t forget to add a "." at the end of the domain/
        hostname. If this is forgotten, this will make the DNS to add the
        domain name to the domain/hostname again. This will cause
	resolving problems.

Ex:

domain.xx.        86400    MX      10 mail.domain.xx.domain.xx.

Illegal characters: 

	Only a-z , 0-9 and - is valid to use. All other characters is
	illegal and can cause the resolving to fail.

General Points:

        Use the latest version of the DNS software for your platform.
        Check for updates regulary, as new versions has the latest
	solutions and information.

Additional reading and references:

        RFC1537 ( RFC1912 )
        ( Common DNS Operational and Configuration Errors )

        "DNS & BIND 2nd Edition" by Paul Albitz & Cricket Liu 
        from O´Reilly & Associates Inc.

        ftp://ftp.ripe.net/internet-drafts/draft-ietf-dnsind-classless-
        inaddr-04.txt
        ( For reverse delegation methods for blocks smaller than /24,
        256 addresses )

        http://www.dns.net/dnsrd/
        ( DNS Resources Directory )

/Hans Niklasson

Email: hasse@swip.net
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