Free secondary/slave 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.
• ipv4 & ipv6.
• DNSSEC compliant.
• Recommended.
• NSD

buddyns.com

• Servers: New York, Arizona, Switzerland, Singapore, Germany.
• Unlimited domains for free (donation based).
• Secondary DNS only.
• Uses Notify or send an email to update DNS immediately.
• Does not allow axfr transfers from buddyns.
• NOT DNSSEC compliant.
• ipv4 & ipv6.
• Recommended.
• DJ Bernstein TinyDNS 1.05

Hurricane Electric

• Dualstack: Supports queries via both IPv4 and native IPv6.
• 5 servers in Fremont CA
• NOT DNSSEC compliant.
• PowerDNS

GratisDNS.dk

• Website is in Danish (I was able to fumble thru the process with the translator built into Google Chrome).
• Five servers (Denmark, Denmark, Ireland, Texas, France)
• Uses notify function.
• ipv4 & ipv6.
• DNSSEC compliant.
• BIND 9

zoneedit.com

• Two domains free.
• Two nameservers for free, more if you pay (they have 19).
• Once a domain is in their system it counts against your two maximum forever, even if you delete it.
• Does not use the notify funtionality.
• axfr transfers can be restricted to specific IP addresses.
• NOT DNSSEC compliant.
• ipv4 only.
• review
• BIND 8

freedns.afraid.org

• One server, ns2.afraid.org, in Texas.
• Uses notify function for instant updating when you make changes.
• AXFR transfer access list.
• DNSSEC compliant.
• ipv4 only.
• BIND 9

Roller Network

• Two servers in Reno Nevada.
• ipv4 & ipv6.
• DNSSEC compliant.
• Bind 9

xname.org

• Three servers on different networks, all in France.
• Unlimited domains.
• Does not use the notify funtionality.
• ns2.xname.org is ipv4 & ipv6
• BIND 9

twisted4life.com

• 10 domains free
• One server, ns1.twisted4life.com, in Kuala Lumpur, Malaysia.
• ipv4 only.
• DNS configuration checker
• DJ Bernstein TinyDNS 1.05

Zerigo.com

• 3 domains free
• IPv6

Other useful DNS Links:

• List of free DNS providers
• Site for exchanging secondary DNS services with others for free: ns2exchange.com
• Online DNS tools:
  • DNSSEC
    • verisign dnssec debugger
    • verisign dnssec test
    • sidn dnssec test
    • DNSviz.net (DNSSEC visualization tool)
    • dnssec validator for google chrome
    • dnssec validator for firefox
  • DNS checking
    • BuddyNS Delegation Lab
    • WebDNSTools.com
    • intoDNS.com
    • DNSinspect.com
    • HowIsMyDNS.com
    • WhatsMyDNS.net (propogation test)
    • RobTex
    • DNScheck
    • DNSTrouble.com
    • registered nameserver lookup tool
    • Men & Mice DNS Analyzing Service
    • dnscheck @ squish.net
    • DNS configuration checker
• DNS servers:
  • nsd (name server daemon) an authoritative only, high performance, simple, and open source name server.
  • unbound a validating, recursive, and caching DNS resolver.
  • knot-dns a high-performance authoritative-only DNS server, supports DNSSEC.
  • maradns
• Some shell scripts I wrote:
  • dnscheck.sh - check the SOA serial numbers at all of the nameservers for a domain.
  • dnsreport.sh - 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