Network

What is IPv6?

IPv6 is version 6 of the Internet Protocol, addressing hosts with 128 bits written as eight hexadecimal groups, such as 2001:db8::1. The space is large enough that carriers assign each subscriber a whole subnet, usually a /64 or wider, so reputation systems score prefixes instead of single addresses. Adoption is broad but far from universal.

Addresses are written as eight groups of four hex digits, with leading zeros dropped and one run of zero groups collapsed to :: - once per address, since a second collapse would be ambiguous. The first 64 bits normally identify the network and the last 64 the interface. Global unicast addresses sit under 2000::/3, link-local addresses under fe80::/10 exist on every interface for local signalling, and there is no broadcast at all; multicast replaced it. In a URL the address goes in square brackets, as in http://[2001:db8::1]:8080.

Subscribers receive a subnet rather than a single address. A carrier typically delegates a /64 to one link or a /56 to a home, and hosts inside configure themselves with SLAAC from router advertisements. Privacy extensions rotate the interface half of the address on a schedule, so one laptop cycles through many addresses in a week. Detection and reputation systems answer that by scoring the prefix, commonly the /64 or /48, because counting individual v6 addresses is pointless when a customer holds billions of them.

Most clients run dual stack and choose a path with Happy Eyeballs, racing an IPv6 connection against an IPv4 one and keeping whichever answers first. That behaviour breaks proxy setups without any visible error. If the proxy handles IPv4 only and the machine has working IPv6, the browser can reach an IPv6-capable target directly and expose the real address, the same failure shape as a DNS leak. SOCKS5 does carry IPv6 destinations natively, using a dedicated address type for them.

Target support is uneven. Many large sites, APIs and anti-bot front ends answer on IPv4 only, so an IPv6-only proxy fails on requests that have nothing to do with blocking. Some access networks go the other way, handing out v6-only service with NAT64 and DNS64 translating for legacy destinations. Test each family separately before blaming a proxy, since a bare connection error tells you nothing about which stack produced it.

Where you meet it

IPv6 reaches most people as a leak or as a compatibility failure. A checker shows a v6 address next to the v4 one you expected, meaning part of your traffic never entered the proxy. Or a scraper that works everywhere returns connection errors against one site that publishes no AAAA record. Deciding whether to route v6 through the proxy or disable it on the interface is a setup choice worth making deliberately.

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Common questions

Can IPv6 leak my real IP address while I use a proxy?

Yes. If the proxy handles only IPv4 and your machine has working IPv6, the browser can prefer the v6 path and connect straight to the target. Route IPv6 through the same proxy, or disable IPv6 on the interface carrying that traffic, then verify with a tester that reports both families.

Are IPv6 proxies worth using?

Only where the target answers over IPv6 and treats it fairly. Search engines and several large platforms are reachable on v6, while plenty of sites and anti-bot services are v4-only, and some score v6 prefixes harshly because bulk allocations are cheap. Check the target's AAAA records and its behaviour before committing.

How do I know whether my connection has IPv6?

Ask a test service that reports both address families, or run a lookup that resolves only AAAA records from the same machine. Working v6 shows a global address outside the fe80:: range and presents that address to sites you visit. If you only have a link-local address, the network gives you no v6 connectivity.

Related terms

IPv4
IPv4 is version 4 of the Internet Protocol, addressing hosts with 32 bits written as four dot-separated octets, which gives roughly 4.3 billion addresses. The top-level pool ran dry in 2011, pushing providers toward private addressing, carrier-grade NAT and a paid transfer market. Nearly all proxy traffic still runs over IPv4 because that is what target sites accept.
IP Address
An IP address is the numeric identifier a device presents on an IP network so packets can be routed to and from it. IPv4 writes 32 bits as four decimal octets, such as 203.0.113.7. IPv6 writes 128 bits as hexadecimal groups, such as 2001:db8::1. Every request a server logs is tied to one.
CGNAT
Carrier-grade NAT is address translation performed by an ISP rather than in the customer's router, putting many subscribers behind one public IPv4 address. Mobile networks depend on it. Each customer holds a private or shared-range address, usually from 100.64.0.0/10, and the carrier rewrites the source address and port on every outbound flow.
NAT
Network Address Translation rewrites the address and port fields of packets as they cross a router, letting many private hosts share one public IP. The router keeps a translation table, mapping each outbound flow to a free public port and reversing the rewrite on replies. Home routers do this for a household; carriers do it for whole regions.
ASN
An Autonomous System Number identifies a network that announces its own IP address ranges to the rest of the internet through BGP. Every routable address sits inside a prefix announced by some AS, so the ASN behind an IP tells you who operates it - a mobile carrier, a hosting provider, a home ISP or a corporate network.
DNS
The Domain Name System turns a hostname such as example.com into the IP addresses a client can connect to. A stub resolver on the device asks a recursive resolver, which walks the root, TLD and authoritative name servers, then caches the answer for the record's TTL. Queries travel on port 53, or over TLS or HTTPS when encrypted.
DNS Leak
A DNS leak happens when a client sends its name lookups outside the proxy tunnel, so queries travel over the real ISP connection while the traffic itself exits on the proxy IP. The resolver operator, and any authoritative server it contacts, then sees a lookup tied to your actual network, region and provider.

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