Free secondary DNS services:

puck.nether.net/dns

• One server in Chicago.
• Unlimited domains.
• Secondary DNS only.
• Does not use the notify funtionality.
• Does not allow axfr transfers from puck.nether.net.
• Recommended.
• BIND 9.2.3rc1 -- 9.4.0a0

www.buddyns.com

• One server in Southern California.
• Unlimited domains for free (donation based).
• Secondary DNS only.
• Send email to update DNS immediately.
• Does not allow axfr transfers from buddyns.
• DJ Bernstein TinyDNS 1.05

zoneedit.com

• 2 domains free.
• 2 nameservers for free, more if you pay (they have 19).
• Once a domain is in their system it counts against your 2 maximum, forever, even if you delete it.
• Does not use the notify funtionality.
• axfr transfers can be restricted to specific IP addresses.
• review
• Recommended.
• BIND 8.3.0-RC1 -- 8.4.4

freedns.afraid.org/secondary

• One server in Illinois.
• Uses notify function for instant updating when you make changes.
• AXFR transfer access list
• BIND 9.2.3rc1 -- 9.4.0a0

xname.org

• Two servers on different networks, both in France.
• Unlimited domains.
• Does not use the notify funtionality.
• BIND 9.2.3rc1 -- 9.4.0a0

twisted4life.com

• 10 domains free
• One server, ns1.twisted4life.com, in Kuala Lumpur, Malaysia.
• Does not accept TCP connections.
• DNS configuration checker
• Not the most reliable.
• DJ Bernstein TinyDNS 1.04

Other useful DNS links:

• ns2exchange.com A list of folks offering to exchange secondary DNS services.
• Online DNS tools:
  • dnscheck @ squish.net
  • registered nameserver lookup tool
  • DNS configuration checker
  • dnsreport.com
• DNS servers:
  • nsd (name server daemon)
  • maradns
• Some shell scripts I wrote:
  • dnsreport - check the SOA serial numbers at all of the nameservers for a domain.
  • dnscheck - check the SOA serial numbers at all of the nameservers for a list of domains. Emails a report if a NS doesn't respond or has an out of date serial number. Suitable for running from cron as a monitoring script.
• DNS Comparision.com
• DNS Reviews.com