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N3 DNS

What is DNS?

The DNS (Domain Name System) allows IP network users, such as those on N3, to use (easier) alphanumeric aliases in place of numeric IP addresses.

A user typing www.nhs.uk into a web browser will get to the website hosted by a server at Internet IP address 217.64.234.65. DNS tells the user's computer that www.nhs.uk is actually at IP address 217.64.234.65. 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.

nhs.uk

nhs.uk 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 a public website. However the NHS also uses nhs.uk on N3 and its other private networks. Using nhs.uk both internally and externally (on the Internet) makes the user experience seamless. An N3 user typing nww.nhs.uk into their browser will get the internal NHS top-level website, but if they type www.nhs.uk they'll get the Internet top level website. This is because N3 has a gateway to the Internet, but they are different websites on different networks.

nhs.uk is the NHS's top level domain. Individual NHS organisations normally have their own sub-domain of nhs.uk, for example: connectingforhealth.nhs.uk. 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 etc is hosted. For example www.connectingforhealth.nhs.uk identifies the web server called ‘www' for the connectingforhealth.nhs.uk (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 nhs.uk domain, the resolving process works for queries about any domain registered and in use. An N3 user DNS request for the IP address of www.bt.com 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.

N3/nhs.uk DNS Set-up

DNS diagram

 1. the Health and Social Care Information Centre and N3SP recommend all N3 users use the N3SP provided internal DNS servers shown as their ‘local' servers for DNS queries. They are at the following N3 network IP addresses: 194.72.7.137 and 194.72.7.142

2. N3SP provides a Network Time Protocol reference source for N3 users to synchronise the clocks in servers and PCs to. Although NTP is shown separately in the diagram, 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 nhs.uk, 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, file transfers, etc.
  • Mail eXchange Record (MX-record) - used to direct messages to email/messaging servers for a domain

Other types of record are also used on the nhs.uk DNS servers:

  • 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 - associates an IP address to a DNS name; effectively the reverse of an A record.

DNS Change Request Process

nhs.uk DNS records are owned and administered by the Health and Social Care Information Centre. NSS in Scotland administers the scot.nhs.uk (sub) domain. N3SP provides and manages the ‘live' DNS service itself.

DNS Change Requests, to change either zone data files or individual DNS records, must be made directly to these bodies. N3SP cannot accept DNS Change Requests from end-users.

For England DNS Change Request forms and contact information click here: http://www.hscic.gov.uk/systemsandservices/addressing/domainnames

For Scotland DNS Change Request forms, contact: nisgtelecom.nss@nhs.net