IPv6 cheat-sheet, part 3: IPv6 multicast
Many IPv6 multicast addresses are well-known to software implementing IPv6, to simplify common routing needs.
Notice: This blog post was originally published on Men&Mice before its acquisition by BlueCat.
The content reflects the expertise and perspectives of the Men&Mice team at the time of writing. While some references may be outdated, the insights remain valuable. For the latest updates and solutions, explore the rest of our blog
Key takeawaysThis key takeaway was generated through LLMs crawling the page and coming up with an overview of the content.This article explains IPv6 multicast, describing how multicast differs from unicast and anycast and how nodes join multicast groups using Multicast Listener Discovery (MLD) to receive 1-to-many traffic. It outlines IPv6 multicast addressing (all multicast addresses share the FF00::/8 prefix), explains how the second octet encodes lifetime and scope, and notes that the address terminates with the interface ID. The article lists well-known IPv6 multicast addresses used by common protocols and services (for example ff02::1 for all nodes, ff02::2 for all routers, ff02::fb for mDNS, and ff02::101 for NTP), highlights that any host can be a sender while only group members are receivers, and points to upcoming content on IPv4-IPv6 tunneling and migration.
How do IPv6 nodes join multicast groups and what roles do different node types play?
Nodes join IPv6 multicast groups by sending Multicast Listener Discovery (MLD) report messages. In IETF terminology used in the article, a node is any IPv6-enabled interface; a router is a node that forwards IPv6 packets not expressly addressed to it; and a host is a node that is not a router. Any host can act as a sender of multicast packets regardless of group membership, but only hosts that have joined the multicast group (i.e., sent MLD reports) will receive packets sent to that group. Hosts may join or leave groups dynamically, and multicast groups are not constrained by local or global geography—membership signaling determines reception.
What is the structure of IPv6 multicast addresses and how is scope indicated?
All IPv6 multicast addresses share the FF00::/8 prefix (first octet FF). The second octet encodes two pieces of information: the lifetime (0 for permanent, 1 for temporary) and the scope, with values like 1 for node-local, 2 for link-local, 5 for site, 8 for organization, and E for global scope. The remainder of the multicast address ends with the interface ID. This structure allows quick identification of multicast addresses (via the FF prefix) and communicates intended reach and duration through the second octet.
Which well-known IPv6 multicast addresses are commonly used by network protocols and services?
The article lists many well-known IPv6 multicast addresses mapped to protocols and services. Examples include ff02::1 (all nodes), ff02::2 (all routers), ff02::5 (all OSPF routers), ff02::6 (all OSPF designated routers), ff02::9 (all RIP routers), ff02::a (all EIGRP routers), ff02::d (all PIM routers), ff02::f (UPnP devices), ff02::11 (all homenet nodes), ff02::12 (VRRP), ff02::16 (all MLDv2-capable routers), ff02::1a (all RPL routers for IoT), ff02::fb (multicast DNS), ff02::101 (NTP), ff02::1:2 (all DHCP agents), ff02::1:3 (LLMNR), and ff02:0:0:0:0:1:ff00::/104 (solicited-node addresses). Site-scoped equivalents include ff05::1:3 (all DHCP servers) and ff05::101 (all NTP servers). These addresses simplify common routing and discovery tasks in IPv6 environments.
Now that we’ve familiarized ourselves with the IPv6 header and the IPv6 address space, let’s take a look at multicast.
Unicast, anycast, multicast
IPv6 packets can be sent, depending on the intended purpose, in a variety of ways:
- unicast: used for 1-to-1 communication; it sends the packet to a specific node. (Certain unicast addresses within the IPv6 address space are reserved. See the previous post for details.)
- anycast: used for 1-to-1-of-many communication; it sends the packet to multiple nodes but only intended to the closest on its route.
- multicast: used for 1-to-many communication; it sends the packet to multiple nodes.
We’re not covering anycast in detail at this moment, but we can — do let us know if that’s something of interest to you!
IPv6 multicast
IPv6 multicast works by nodes* joining multicast groups by sending Multicast Listener Discovery (MLD) report messages.
(*Little terminology from IETF: node is an interface enabled for IPv6. Router is any node that forwards IPv6 packets that are not expressly addressed to it. Host is any node that’s not a router.)
Multicast groups aren’t constrained by local or global (network) geography. Whether the host is on the local network or on the internet, as long as it’s signaling to join a multicast group, it can receive multicast packets sent to that group.
Any host can be a sender, whether it’s part of the multicast group or not. Only hosts part of the multicast group are receivers. Hosts can join or leave multicast groups dynamically at any time.
IPv6 multicast addresses: FF00::/8
All IPv6 multicast addresses share the prefix of FF00::/8.
- The first octet is FF (1111 1111). This way you can tell at a glance if an IPv6 address is intended for multicast or not.
- The second octet defines:
- the lifetime (0 for permanent multicast; 1 for temporary)
- and scope (1 for node, 2 for link, 5 for site, 8 for organization, and E for global scope).
The multicast address ends with the interface ID.
Well-known IPv6 multicast addresses
Many IPv6 multicast addresses are well-known to software implementing IPv6, to simplify common routing needs.
| Multicast Address | Description |
|---|---|
| ff02::1 | all nodes |
| ff02::2 | all routers |
| ff02::5 | all OSPF (Open Shortest Path First) routers |
| ff02::6 | all OSPF DRs (OSPF Designated Routers) |
| ff02::9 | all RIP (Routing Information Protocol) routers |
| ff02::a | all EIGRP (Enhanced Interior Gateway Routing Protocol) routers |
| ff02::d | all PIM (Protocol Independent Multicast) routers |
| ff02::f | UPNP (Universal Plug and Play) devices |
| ff02::11 | all homenet nodes |
| ff02::12 | VRRP (Virtual Router Redundancy Protocol) |
| ff02::16 | all MLDv2-capable routers |
| ff02::1a | all RPL (Routing Protocol for Low-Power and Lossy Networks) routers (used in Internet of Things (IoT) devices) |
| ff02::fb | multicast DNS IPv6 |
| ff02::101 | network time (NTP) |
| ff02::1:2 | all DHCP agents |
| ff02::1:3 | LLMNR (Link-Local Multicast Name Resolution) |
| ff02:0:0:0:0:1:ff00::/104 | solicited node address |
| ff02:0:0:0:0:1-2:ff00::/104 | node information query |
| ff05::1:3 | all DHCP server (site) |
| ff05::101 | all NTP server (site) |
(Did we or did we not promise a veritable smorgasbord of acronyms?)
Looking to Automate?
See our automation video playlist here.
More IPv6 coming up!
Next time we’ll be taking a look at IPv4-IPv6 tunneling and the particularities of migrating from IPv4 to IPv6.
After that, we have one last post to cover the remaining sections on our cheat-sheet, including useful Linux commands.
As always, do let us know if there’s a particular part of IPv6 (whether covered in here or not) you’d like to know more about!
Related content
How to map your network with user-defined links in Integrity X
Map your network with user-defined links in Integrity X to define and manage custom relationships, such as dual-stack and NAT environments.
Automate your DDI modernization path by migrating with Micetro
Automate cross-platform DNS and DHCP migration with Micetro to reduce risk, eliminate manual effort, and modernize infrastructure faster.
Your journey to intelligent NetOps begins at Cisco Live
Visit BlueCat’s booth or book a meeting now to learn more about how our solutions can help you build a network that supports constant change.
Replace BIND and ISC with Micetro DNS/DHCP Server (MDDS)
Tired of patching and manually configuring BIND DNS and ISC DHCP? Discover how Micetro MDDS appliances can replace them for modern DDI.