Glossary
2001:db8::/32
Address block reserved for documentation and examples. The addresses are never used on the internet. It is the block shown at the top of the page. Read more
464XLAT
Technique that lets IPv4-only applications work on an IPv6-only network. The traffic is translated twice: by CLAT on the client and by NAT64 in the network. Read more
6bone
IPv6 test network that was in operation from 1996 to 2006. Participants were connected with tunnels over IPv4 and got addresses from the 3ffe::/16 block. Read more
A record
DNS record that gives the IPv4 address for a name. The IPv6 equivalent is the AAAA record. Read more
AAAA record
DNS record that gives the IPv6 address for a name, in the same way that an A record gives the IPv4 address. Pronounced "quad-A". Read more
ARP
Address Resolution Protocol. Finds out which MAC address belongs to an IPv4 address on the local network. In IPv6, ND takes care of this. Read more
BGP
Border Gateway Protocol. The protocol that operators and larger networks use to tell each other which addresses they have. Anyone with their own addresses announces them with BGP, either themselves or through their operator. Read more
CGNAT
Carrier-Grade NAT. The operator lets many customers share the same public IPv4 address, often as a second layer of NAT outside the customer's own router. Read more
CLAT
Customer-side Translator. The client's part of 464XLAT, which translates IPv4 traffic from applications into IPv6. Available in iOS, Android, ChromeOS and macOS, and in Windows 11 under the name WinCLAT. Read more
Communications operator
Abbreviated KO in Swedish. The party that runs an open network, such as a municipal network, on behalf of the network owner and lets in service providers that sell subscriptions on it. If the communications operator's platform does not handle IPv6, no service provider on the network can deliver it. Read more
Content delivery network
Abbreviated CDN. A network of servers around the world that delivers a website from a location close to the visitor. The big CDNs support IPv6, so a website behind one often gets it with a single setting. Read more
DAD
Duplicate Address Detection. Before a device starts using an IPv6 address, it asks on the local network whether anyone else already has it. Read more
DHCP
Dynamic Host Configuration Protocol. A server hands out an IPv4 address, default gateway and DNS servers to the devices on the network. Read more
DHCP snooping
Protection in the switch against rogue DHCP servers, such as a home router plugged in the wrong way round. Only ports designated as trusted are allowed to answer DHCP requests. The IPv6 equivalent is called DHCPv6 snooping, and against rogue RAs there is RA Guard. Read more
DHCPv6
DHCP for IPv6. Can hand out addresses, entire prefixes and settings such as DNS servers, but not the default gateway, which always comes from the router's RA. Read more
DNS
The Domain Name System, which translates names like ipv6.help into IP addresses. Read more
DNS64
DNS server that makes up an AAAA record for names that only have an A record, by putting the IPv4 address at the end of the NAT64 prefix. The traffic then goes to NAT64. Read more
Dual stack
Running IPv4 and IPv6 side by side on the same network and the same devices. The most common way to introduce IPv6 without turning off IPv4. Read more
End-to-end
The principle that any device on the internet should be able to reach any other directly, without anything along the way rewriting the traffic. Read more
GRE
Generic Routing Encapsulation. Simple tunnelling protocol that encapsulates traffic in IP packets, for example IPv6 in IPv4. The tunnel is not encrypted and does not pass through NAT or CGNAT without extra work. Read more
IANA
Internet Assigned Numbers Authority. Manages the global address space and allocates large address blocks to the regional internet registries (RIRs). Read more
ICMPv6
The control protocol in IPv6. Carries error messages and ping, just like ICMP in IPv4, but also ND and MLD. That is why it must not be blocked in the firewall. Read more
IoT
Internet of Things. Sensors, meters, lamps and other small devices that are connected. The number of devices quickly becomes very large, which is why most new IoT networks are built on IPv6. Read more
IPsec
Protocol that encrypts and authenticates IP traffic, often in VPNs. Works with both IPv4 and IPv6. IPv6 used to be required to support IPsec, but traffic was never encrypted automatically, and the requirement was dropped in 2011. Read more
IPv4
Version 4 of the Internet Protocol, from 1981. Addresses are 32 bits long, which gives about 4.3 billion addresses. Written as, for example, 192.0.2.1. Read more
IPv6
Version 6 of the Internet Protocol and the successor to IPv4. Addresses are 128 bits long. Written as, for example, 2001:db8::1. Read more
IPv6-mostly
Network where clients that can manage with IPv6 alone do so, while the others still get IPv4. The client asks for DHCP option 108 and stops using IPv4 if the server responds with it. IPv4 services are then reached through CLAT and NAT64. Read more
Layer 2 and layer 3
Layers in the OSI model. At layer 2, traffic is carried with MAC addresses through switches within a local network. At layer 3, it is routed with IP addresses between networks. In an open municipal network, this determines whether the ISP reaches the customer's router directly (layer 2) or whether the communications operator routes the traffic (layer 3). Read more
Link-local
Address that is only valid on the local network and is never routed further. Every device with IPv6 gives itself such an address, starting with fe80::, even when the network has no IPv6 connectivity to the internet. ND and RA use them. Read more
MAC address
The hardware address of a network interface, 48 bits, written as, for example, 00:00:5e:00:53:01. Used to send traffic within the local network, at layer 2. Read more
MITM
Man-in-the-middle. An attack where someone places themselves between two parties and reads or alters the traffic. On the local network this is often done with spoofed ARP or ND replies, or with a rogue DHCP server or router. Protections exist for both IPv4 and IPv6. Read more
MLD
Multicast Listener Discovery. Devices tell the network which multicast groups they are listening to. Equivalent to IGMP in IPv4. MLDv2 is the current version. Read more
MTU
Maximum Transmission Unit. The largest packet that fits on a link, usually 1500 bytes on Ethernet. IPv6 requires at least 1280 bytes. A tunnel takes up some space in every packet and therefore gives a lower MTU, often 1420 bytes with WireGuard. Read more
MX record
DNS record that specifies which server receives email for a domain. For email to be reachable over IPv6, that server must have an AAAA record. Read more
NAT
Network Address Translation. A router rewrites the addresses in the traffic so that many devices with private addresses can share one public address. Read more
NAT64
Translates between IPv6 and IPv4, so that an IPv6-only device can reach services that are only available over IPv4. Often uses the prefix 64:ff9b::/96. Called PLAT when it is part of 464XLAT. Read more
ND
Neighbor Discovery, also NDP. Finds neighbours and routers on the local network using ICMPv6 and replaces ARP from IPv4. Read more
Option 18
Interface-ID in DHCPv6. The switch or router relaying a DHCPv6 request adds the port the request came in on, so that the server can log which connection got which address. Used for traceability. Read more
OT
Operational Technology. The networks and systems that control physical things: machines, ventilation, heating, water and lighting. The equipment often stays in place for 10 to 15 years. Read more
PA addresses
Provider Aggregatable. Addresses that belong to the operator and that the customer borrows for as long as the contract lasts. If you change operator, you get new addresses and have to renumber the network. The opposite is PI addresses. Read more
Packet Too Big
ICMPv6 message saying that a packet is too large for a link along the path, and how large it may be. Routers never fragment packets in IPv6, so the sender needs the message in order to send smaller packets. If it is blocked in a firewall, connections can hang. Abbreviated PTB. Read more
PI addresses
Provider Independent. Addresses that an organisation has received directly from an RIR and can take with it when it changes operator. The opposite is PA addresses, which belong to the operator. Read more
Port batching
Also port block allocation. A way to avoid logging every translation in CGNAT: each customer gets a fixed public IPv4 address and a fixed block of ports, for example 64 of them. The address and port are then enough to identify the customer, but the customer can only have as many simultaneous connections as the block allows. Read more
PREF64
Option in the router's RA that tells clients which prefix NAT64 uses. CLAT needs it to know where to send the translated traffic. Read more
Prefix
The first part of an address, the part that identifies the network. The length is written after a slash: in 2001:db8::/32 the first 32 bits belong to the network, and the rest can be divided into your own networks and addresses. Read more
Prefix delegation
Abbreviated PD. The router receives an entire prefix from the operator via DHCPv6, for example a /56, and divides it into a /64 for each network behind it. Read more
Private addresses
The IPv4 blocks 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16, which anyone may use on their own network but which cannot be reached from the internet. Defined in RFC 1918. Read more
PTS
The Swedish Post and Telecom Authority, the Swedish government agency for electronic communications and postal services. PTS can recommend IPv6 but cannot require it. Read more
RFC
Request for Comments. The numbered documents that describe the internet's protocols and standards. Read more
RIPE NCC
The regional internet registry for Europe, the Middle East and parts of Central Asia. Often just called RIPE. Read more
RIR
Regional Internet Registry. Five organisations that allocate IP addresses, each in its own part of the world: AFRINIC, APNIC, ARIN, LACNIC and RIPE NCC. Read more
RS/RA
Router Solicitation and Router Advertisement. A device asks for routers (RS), and the router responds with the prefix used on the network and how the device should obtain its address (RA). Read more
SCADA
Supervisory Control and Data Acquisition. Systems that monitor and control equipment in, for example, industry, energy, water and buildings, often over long distances. Part of OT. Read more
SixXS
Tunnel broker that until 2017 provided free IPv6 connectivity through tunnels over IPv4, for those who could not get IPv6 from their operator. Read more
SLAAC
Stateless Address Autoconfiguration. The device builds its own IPv6 address from the prefix in the router's RA, without any DHCP server. Read more
Stateful firewall
Firewall that keeps track of which connections have been opened from the inside and only lets in traffic that belongs to them. Also called stateful inspection. This is what protects the network, with or without NAT. Read more
TCP/IP
Collective name for the internet's protocol suite. TCP provides a reliable connection where everything arrives and in the right order, while IP handles addressing and routing. Read more
Thread
Wireless network for small, low-power devices, built on IPv6. Used by Matter, the smart home standard, and by DALI+ for lighting. Read more
Tunnel
Traffic that is encapsulated in another protocol to get across a network that cannot carry it directly, for example IPv6 over IPv4. Read more
UDP
User Datagram Protocol. Sends individual packets without setting up a connection and without any guarantee that they arrive. Used by DNS, voice and video, among others. Read more
VoLTE
Voice over LTE. Calls on the 4G network that are carried as IP traffic instead of over the old telephone network. At several mobile operators, including Telia, this traffic runs over IPv6. Read more
VPN
Virtual private network. An encrypted tunnel that connects a device or a network to another network over the internet. Read more
WireGuard
Modern VPN protocol that is easy to set up and runs over UDP. Handles IPv4 and IPv6 both inside and outside the tunnel, and works behind NAT and CGNAT. Read more