Some organisations may not wish to delegate their entire domain to the Janet Primary DNS service, but still want to benefit from using the automatic failover feature and/or be able to redirect selected records in the event that their primary domain becomes unavailable. One option that could allow you to achieve this is to delegate a subdomain to the Janet Primary DNS service, and populate that with the address records that need to fail over or be manually managed in the event the primary DNS server fails.

This subdomain would be mastered on the Janet DNS Web portal in the normal way. It should probably only be populated with IPv4 and IPv6 address records, and failover TXT records. For example, if you delegated a sub domain, external.site.ac.uk to us, your local DNS would need to contain nameserver records pointing external.site.ac.uk to our DNS servers, and nothing else. You would then populate external.site.ac.uk using the DNS web portal. For example, you may add:-

www.external.site.ac.uk. 300 IN A 10.1.1.80

Then on your local primary server you could point your webserver to this record with:-

www.site.ac.uk. IN CNAME www.external.site.ac.uk.

Now www.site.ac.uk will resolve via www.external.site.ac.uk to address 10.1.1.80. If you changed the address record for www.external.site.ac.uk, the address for www.site.ac.uk would also change. You can set up as many address records as you need to, and in the event of failure of your local DNS server or services you could modify them either manually or by using automatic failover as you deem most appropriate.

Important Note:-

The delegated subdomain is still dependent on the domain it is delegated from, so for it to work when your site is unavailable the delegating domain needs to have a suitably long expire time
set in the SOA, many sites opt for about 6 weeks. You must also have an offsite secondary that can continue serving your domain even when your site and your primary nameservers are unavailable. If you do not already have one, the Janet secondary nameserver service is worth considering.

For further information

If you are currently managing your own DNS services, but would like to discuss how Janet could help with your DNS resilience plans or additional requirements please contact help@jisc.ac.uk