As part of the HSCN service provision, a centrally hosted Domain Name System (DNS) is provided in the core. However, LAN hosts may not always access these services directly, but may instead reference one or a thread of locally hosted DNS name servers, before eventually referencing the national DNS. An example may be when a host attempts to establish a connection to another IP host, it will first check its local HOSTS file (if there is one) for the name of the remote host. If the remote host is not in the HOSTS file, the host will send a query to its LAN hosted primary DNS name server. The primary name server may well not contain the information about the particular destination host; in that case, the query must be forwarded to another name server that is higher up in the domain name hierarchy. This is DNS forwarding. When re-addressing a LAN environment, though the national hosted DNS address does not change, it is essential to ensure locally hosted DNS are updated to reflect the new address scheme.
Guidance for IP address migration and key services
This section covers some of the key services that need to be considered when migrating from one IP address scheme to another, and the appropriate action required to ensure minimal disruption. Further guidance can be found in the HSCN technical guidance.
Domain Name System forwarding
The HSCN core DNS may also cross reference locally hosted DNS servers at end user sites. This is DNS delegation. When re-addressing a LAN environment, it is essential to ensure changes to locally hosted DNS servers used for delegation are registered with DNS servers that sit higher up the DNS hierarchy.
Locally hosted web site domain names and their associated IP addresses are registered and updated using the DNS registration form on the NHS Digital website. When changing the external IP address scheme of a locally hosted service, it is essential this form is completed to ensure the correct DNS name entry and IP address appears within the national DNS table.
To ensure the changeover is co-ordinated in a controlled manner, the end user site can specify to NHS Digital when the change is to be activated.
Simple Mail Transfer Protocol (SMTP) servers
Locally hosted SMTP servers and their associated domain names and IP addresses are registered and updated using the SMTP registration form on the NHS Digital website. A Mail Exchanger (MX) record is an entry in a DNS table which controls where mail for a particular domain name is sent. This information is also registered and updated via the SMTP registration form. When changing the external IP address scheme of a locally hosted SMTP mail server, it is essential this form is completed to ensure the correct domain name entry and IP address appears within the national DNS. To ensure the changeover is coordinated in a controlled manner, the end user site can specify to NHS Digital when the change is to be activated by contacting DNSTeam@nhs.net.
End sites that host or access services that authenticate using the IP address need to ensure changes to advertised IP addresses at either the client or host site, are co-ordinated at both end user sites.
GP firewall rule table
Changes to GP firewall rule tables to allow new incoming sessions into the GP LAN should be requested through your network service provider.