NETWORK
IPv4 vs IPv6Address formats, differences and coexistence
IPv4 uses 32-bit addresses written as four decimal numbers (192.0.2.1) and ran out of new space in 2011; IPv6 uses 128-bit addresses written in hexadecimal groups (2001:db8::1) and has enough for every device to have a public address without NAT. Both run in parallel on most networks today, and a device usually has one of each.
Address size and notation
| IPv4 | IPv6 | |
|---|---|---|
| Bits | 32 | 128 |
| Written as | Four decimal octets: 203.0.113.10 | Eight groups of four hex digits: 2001:db8:85a3::8a2e:370:7334 |
| Shorthand | None | Leading zeros dropped; one :: for a run of zero groups |
| In URLs | http://203.0.113.10:8080/ | http://[2001:db8::1]:8080/ (brackets required) |
| Loopback | 127.0.0.1 | ::1 |
| Unspecified | 0.0.0.0 | :: |
Why IPv6 exists
IPv4's 4.3 billion addresses were exhausted at the registry level in 2011 (IANA) and regionally over the following years. NAT stretched the space by hiding whole networks behind one address, but it complicates anything that needs inbound connections and layers up in carrier-grade NAT. IPv6 restores the original end-to-end model: each network gets a /64 with 18 quintillion addresses, and each device gets a globally unique one.
Configuration differences
IPv4 devices usually get an address from DHCP. IPv6 devices can configure themselves with SLAAC (Stateless Address Autoconfiguration): the router advertises the prefix, and the device appends an interface identifier. DHCPv6 exists for networks that want central control or need to hand out DNS servers to clients that do not support the router-advertisement option for DNS.
Coexistence
Most networks run dual stack: every device has both an IPv4 and an IPv6 address, and applications prefer IPv6 when the destination has an AAAA record and the path works. "Happy Eyeballs" logic in browsers tries both and uses whichever connects first, so a broken IPv6 path usually causes slight delay rather than failure.
Where native IPv6 is unavailable, transition mechanisms carry one protocol inside the other (6to4, Teredo, 464XLAT, DS-Lite). Mobile carriers commonly run IPv6-only networks with 464XLAT for IPv4 applications.
Security and firewalling
- No NAT does not mean no firewall. Consumer routers apply a stateful IPv6 firewall by default; make sure it stays on.
- Address privacy: temporary addresses (RFC 8981) rotate so a device cannot be tracked across sites by its address.
- Dual-stack blind spots: a firewall or monitoring rule written only for IPv4 leaves IPv6 unfiltered. Audit both.
Checking your setup on Windows
ipconfigLook for IPv6 Address (global, starting 2xxx or 3xxx) as opposed to Link-local IPv6 Address (fe80::), which every interface has regardless. Test reachability:
ping -6 ipv6.google.com
nslookup -type=AAAA example.comA successful ping -6 means routed IPv6 works end to end. See ping and nslookup.
Frequently asked questions
Should I disable IPv6 on Windows?
Microsoft recommends leaving it enabled; several Windows features assume it exists and it is used on the local link even without internet IPv6. Disabling it rarely fixes anything and occasionally breaks things. If you must prefer IPv4, change the prefix policy rather than unbinding IPv6.
What does :: mean in an IPv6 address?
A run of one or more all-zero groups, compressed. It may appear once per address. 2001:db8:0:0:0:0:0:1 becomes 2001:db8::1.
Why does my PC have several IPv6 addresses?
Normal. Every interface has a link-local fe80:: address; if IPv6 is routed, it also has a stable global address and one or more temporary privacy addresses that rotate.
Is IPv6 more secure than IPv4?
Not inherently. IPsec support is built into the specification but optional in practice. The bigger security effect is the absence of NAT: every device can be publicly addressable, so the firewall must do the job NAT incidentally did.