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HSCN / Transition Network DNS

This document provides an overview of DNS on HSCN and TN and the DNS change request process

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What is DNS?
How does DNS work?
HSCN/TN/ logical DNS configuration
DNS records
DNS change request process

What is DNS? 

The DNS (Domain Name System) allows IP network users to use alphanumeric aliases in place of numeric IP addresses.

For example, a user typing into a web browser will get to the website hosted by a server at internet IP address DNS tells the user's computer that is actually at IP address The user's computer, the server hosting the website and the network on their own only understand IP addresses.

DNS also lets operators move servers and services to different IP addresses invisibly, whilst keeping the DNS naming the same for users. is the registered internet domain for the UK National Health Service. This means it is for internet use - for instance, when sending email outside the NHS or when an NHS organisation wants to access a public website. However, the NHS also uses on HSCN, the Transition Network (TN) and its other private networks. 

Using both internally and externally (on the internet) makes the user experience seamless. An HSCN/TN user typing into their browser will get the internal NHS top-level website, but if they type they'll get the internet top level website. This is because the TN has a gateway to the internet, but they are different websites on different networks. is the NHS's top level domain. Individual NHS organisations normally have their own sub-domain of, for example: Sub-domains are normally just called domains, when they're being talked about alone. A full DNS address (technically known as a URL) includes the hostname prefix; the name of a server where a website is hosted. For example identifies the web server called 'www' for the (sub!) domain.

How does DNS work?

DNS works by user (client) computers sending queries to a local DNS server to get the IP addresses they need. This is called resolving. Domain name data is distributed and/or delegated amongst a number of name servers. Often the local name server doesn't hold all the data requested, even though local servers do store (cache) some answers to recent DNS queries. If the answer isn't cached, the local server checks with other name servers to get the data. This is known as recursive operation. This process continues until the definitive DNS information (record) for a domain is found on an authoritative DNS server. Although previous examples have used the domain, the resolving process works for queries about any domain registered and in use. A TN (formerly N3) user DNS request for the IP address of would be resolved in the same way.

Because DNS is so important there should always be at least two DNS servers for any domain for resilience. These are often called primary and secondary, although they may share DNS requests more equally than the names suggest, depending on set up.

HSCN/TN/ logical DNS configuration

The below diagram shows the logical DNS configuration used across HSCN/TN


  1. NHS Digital recommend that all TN users continue to use the current provided internal DNS servers shown as their 'local' servers for DNS queries. They are at the following network IP addresses: and
  2. The current provision of a Network Time Protocol (NTP) reference source will remain in place for all users to synchronise the clocks in servers and PCs. NTP is currently shown separately in the diagram, however the NTP platform will be refreshed as part of TN services. The reference source is actually available from the same IP addresses (above) as the internal DNS service.

DNS records

Data for a domain, such as, is arranged in zone data files with a number of (resource) records. The most important and most often used are the:

  • address record (A record) - used to direct users to live servers for web browsing and file transfers for example
  • mail exchange record (MX-record) - used to direct messages to email/messaging servers for a domain

Other types of record used on the DNS servers are:

  • start of authority (SOA): defines the start of a zone data file, includes information on: 
    • the name server with ultimate authority for the domain
    • who to contact about the domain
  • name server (NS): defines one or more name servers with definitive DNS information
  • Canonical Name/alias (CNAME): defines additional aliases for an IP address (as alternative to multiple A records)
  • Pointer (PTR): a 'reverse lookup' record that associates an IP address to a DNS name - effectively the reverse of an A record

DNS change request process DNS records are owned and administered by NHS Digital. NSS in Scotland administers the (sub) domain. The TN provider will continue to manage the 'live' DNS service for the foreseeable future.

DNS change requests, to change either zone data files or individual DNS records, must be made directly to these bodies. The HSCN/TN service provider cannot accept DNS change requests from end-users.

Find England DNS change request forms and contact information

Have a question? Call us on 0300 303 5678 or contact

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