What is Custom DNS?
Updated: 3 days ago
Custom DNS means choosing which recursive DNS resolver your device or network sends DNS queries to instead of simply using the resolver supplied automatically by your ISP, router or local network. It changes who performs recursive DNS resolution for you; it does not change your broadband connection, public IP address or the authoritative DNS records for a website.
The practical reasons for using custom DNS include resolver policy, filtering, privacy choices, reliability, encrypted DNS support and sometimes lookup performance. But a custom resolver is not automatically faster, more private or more secure: those properties depend on the resolver and how your device reaches it.
What does Custom DNS actually change?
Most devices use a stub resolver that sends DNS questions to a recursive resolver. RFC 1034 describes resolvers as the software that obtains information from name servers, while RFC 8499 distinguishes stub resolvers from recursive resolvers. A custom DNS setting normally changes the upstream recursive resolver address used by that stub or by a forwarding router.
For example, instead of accepting DNS servers learned automatically through your broadband connection, DHCP or router configuration, you can specify another resolver. The resolver then answers from cache when possible or performs the necessary DNS resolution on your behalf.
How does Custom DNS work?
When you type a domain name into an application, your device needs DNS information such as an IPv4 or IPv6 address. With custom DNS configured, that request is directed to the resolver you selected. The resolver may answer from its cache or query other DNS servers until it can return an answer.
Your application requests information for a domain name.
The operating system's stub resolver checks local information and cache where applicable.
The query is sent to the configured recursive resolver, which is your custom DNS service if you changed it.
The recursive resolver answers from cache or performs resolution using the DNS hierarchy.
The answer is returned and the application can connect to the destination address.
Custom DNS vs your ISP's default DNS
An ISP-provided resolver and a third-party custom resolver perform broadly the same core recursive DNS role. The important differences are operational: cache behaviour, network location, filtering policy, logging and privacy policy, DNSSEC validation, encrypted transport support, resilience and how the resolver's network reaches authoritative DNS infrastructure.
Default ISP DNS is often configured automatically and may be topologically close to the broadband connection.
Custom DNS gives you deliberate control over the recursive resolver you use.
Changing resolver can alter filtering or parental-control behaviour.
A geographically or topologically different resolver can sometimes change which CDN edge an application is directed towards.
A third-party resolver creates a different trust relationship: that resolver can receive your DNS queries unless the architecture or protocol prevents it.
Does Custom DNS make broadband faster?
Not in the way a faster broadband package does. DNS lookup time is only one part of opening a new destination, and many answers are cached. A resolver with a warm cache, low network latency and responsive infrastructure can reduce some lookup delays, while a distant or overloaded resolver can make them worse.
Techie Broadband practical analysis: if one uncached lookup fell from 40 ms to 15 ms, the lookup itself would save 25 ms. That does not turn a 100 Mbps broadband line into a faster line and it does not make an already-established download transfer at a higher bit rate. The effect is on name-resolution delay, not line capacity.
Can Custom DNS improve privacy?
It can change who can observe your DNS queries, but changing the resolver address alone does not automatically encrypt DNS. Traditional DNS commonly uses port 53 and does not by itself provide transport encryption between your device and recursive resolver.
If privacy on that link matters, read What is DNS over HTTPS? and What is DNS over TLS?. DoH and DoT can protect DNS queries in transit to a compatible resolver, but the resolver itself still needs the information required to answer the query.
Custom DNS, DNSSEC and encrypted DNS are different things
Custom DNS: choosing a recursive resolver rather than simply using the automatically supplied one.
DNSSEC: a mechanism that lets validating resolvers cryptographically verify signed DNS data; it does not encrypt DNS queries.
DNS over HTTPS (DoH): DNS carried over HTTPS to a compatible resolver.
DNS over TLS (DoT): DNS carried over a dedicated TLS connection to a compatible resolver.
VPN: a broader encrypted tunnel that can carry network traffic; it is not the same thing as changing DNS.
For the wider encryption context, see What is TLS (Transport Layer Security)? and What is VPN (Virtual Private Network)?.
Where can you configure Custom DNS?
The exact control point matters because a setting on one device and a setting on the router have different scope.
Router: can provide your chosen resolver to devices on the home network, depending on router and DHCP behaviour.
Operating system: can override the network-provided resolver for that device.
Browser or application: some software can use its own encrypted DNS setting independently of the operating system.
VPN client: may supply or enforce DNS servers while the tunnel is active.
Local resolver or filtering appliance: advanced networks can run a local caching or filtering resolver and forward queries upstream.
IPv4 and IPv6 Custom DNS settings
A network may have both IPv4 and IPv6 connectivity, so check both protocol families when changing DNS. Configuring only an IPv4 resolver does not necessarily control every possible DNS path on a dual-stack device.
If you need the addressing background first, see What is IPv4? and What is IPv6?.
Should you change DNS on the router or each device?
Router-level configuration is useful when you want a consistent default for many devices. Device-level configuration gives more granular control and can be useful for testing. However, applications with their own encrypted DNS implementation may not follow the resolver handed out by the router or operating system.
The right choice therefore depends on whether you want network-wide policy, per-device policy or application-specific behaviour. Verify the actual query path rather than assuming a router setting controls every application.
What should you compare before choosing a Custom DNS resolver?
Privacy and logging policy: what query or client information is retained, and for how long?
Filtering policy: is the resolver deliberately blocking malware, adult content or other categories?
DNSSEC validation: does the service validate signed DNS data?
Encrypted DNS support: does it support DoH, DoT or another suitable encrypted transport?
Reliability: is the service engineered with resilient anycast or other redundant infrastructure?
Latency from your connection: measure from your own location rather than relying on a universal 'fastest DNS' claim.
ECS behaviour: EDNS Client Subnet can affect privacy and location-sensitive DNS answers where used.
Operational transparency: are policies, addresses and technical documentation clearly published?
Can Custom DNS bypass ISP blocking or parental controls?
Sometimes a DNS-based block can be affected by changing resolver, but that does not mean custom DNS universally bypasses network controls. Blocking can be implemented at several layers, and managed networks can restrict or redirect DNS traffic.
Changing DNS can also unintentionally remove protections you expected, such as ISP or router-level parental controls and malicious-domain filtering. Treat resolver policy as part of your security and household configuration, not merely a speed tweak.
Custom DNS and CDN performance
DNS can influence which server or content-delivery-network edge a service returns to you. Some DNS systems use resolver location, and some use EDNS Client Subnet where supported, to tailor answers. A resolver that is topologically distant can therefore occasionally produce a different content path.
This is one reason there is no single DNS resolver that is guaranteed to be fastest for every UK broadband connection, service and location. Test the applications you actually use.
How to test a Custom DNS resolver properly
Record the existing automatic DNS settings so you can restore them.
Change DNS on one test device first rather than the whole network.
Confirm which resolver addresses the device has actually received or configured.
Clear the local DNS cache if you need to remove cached answers from the comparison.
Query several domains repeatedly and distinguish cached from uncached results.
Check normal browsing, streaming, gaming launchers and any work VPNs or security tools you rely on.
Test IPv4 and IPv6 behaviour on a dual-stack connection.
If using DoH or DoT, verify that encrypted DNS is actually active rather than assuming the custom IP address provides encryption.
Restore the previous settings if reliability, filtering or application behaviour becomes worse.
Troubleshooting Custom DNS problems
No websites resolve: confirm the resolver IP addresses are correct and reachable.
Some sites fail: compare the result with the automatic resolver and check DNSSEC or filtering behaviour.
Custom DNS appears ignored: check browser-level DoH, VPN DNS settings, IPv6 resolver settings and router DNS interception.
Browsing feels slower: compare query latency and cache behaviour; do not rely on one lookup.
Parental controls stop working: the previous controls may have depended on the ISP or router resolver.
VPN connection behaves strangely: the VPN may intentionally supply its own DNS configuration to avoid leaks or reach internal names.
Local device names stop resolving: public recursive resolvers do not necessarily know names that were provided by your router or private DNS zone.
Custom DNS on UK broadband
The principle is independent of whether your access connection is FTTP, FTTC, cable, fixed wireless or mobile broadband. What varies is the ISP, router, product and device configuration. Some provider-supplied routers expose DNS controls; others may offer fewer options, while using your own router can provide more control where the service permits it.
Do not assume that changing DNS changes routing through the access network. Your broadband packets still traverse the relevant ISP and access infrastructure; the DNS resolver is simply one service your devices contact.
Common Custom DNS misconceptions
'Custom DNS gives me a new IP address.': It does not change your public broadband IP address.
'Custom DNS is a VPN.': It is not an encrypted tunnel for all traffic.
'Custom DNS is always faster.': Resolver performance varies by network, cache state, destination and location.
'Changing DNS automatically encrypts it.': Encryption requires a protocol such as DoH or DoT and compatible configuration.
'DNSSEC encrypts DNS.': DNSSEC authenticates signed DNS data; it does not provide query confidentiality.
'Router DNS settings control every app.': Applications, VPNs and encrypted DNS clients can use another resolver path.
Frequently asked questions
Is Custom DNS safe?
It can be, provided you choose a trustworthy resolver and configure it correctly. The security and privacy properties depend on the resolver's operation, validation, filtering, logging and transport configuration.
Does Custom DNS change my IP address?
No. It changes the resolver used for DNS queries, not the public IP address assigned to your broadband connection.
Is Custom DNS the same as private DNS?
Not necessarily. Custom DNS simply means choosing a resolver. 'Private DNS' is used by some platforms for encrypted DNS features, so check what the operating system or application specifically means.
Can Custom DNS reduce ping in games?
Usually not in a sustained in-game sense. DNS may affect the initial lookup or occasionally which service endpoint is selected, but it does not directly reduce the network round-trip time to an already selected game server.
Should I use the same DNS on IPv4 and IPv6?
On a dual-stack network, configure and test both protocol families if you want consistent resolver policy. Otherwise some queries may follow a different configured path.
Key takeaway
Custom DNS gives you control over the recursive DNS resolver your devices use. That can change resolver policy, filtering, privacy relationships, encrypted DNS options and sometimes lookup performance, but it does not increase broadband line speed, replace a VPN or automatically encrypt DNS. Choose a resolver for its documented behaviour, then verify the actual DNS path on your own network.
To explore the related technical concepts used in this Custom DNS guide, visit our broadband terminology guide.
