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IPv6 Broadcasting

Unit: 4 Lesson: 5

yelling at nodes but in mandarin a foreign language now

Unicast addressing in IPv6 also refers to a single network interface, just like in IPv4. However, IPv6 addressing is scoped, meaning addresses can refer to a portion/region of the network. Global scoping provides the same functionality as public addressing in IPv4, while link-local addressing provides the same as private addressing.

  • [i] Apparently a max-bit IPv6 address is the same as a broadcast transmission, i.e. ff:ff:ff:ff:ff:ff

A table of all the IPv6 prefixes can be found here.

Global Addressing

Routable over the Internet, equivalent to public IPv4 addresses.

  • first 3 bits (0b001) indicate that this is the global scope
  • next 45 bits are the Network ID
  • next 16 bits is the subnet
  • last 64 bits is the Interface ID

The Interface ID can be derived from a MAC-Address of an interface. This new ID is known as an EUI-64 ID. The derivation process takes the old MAC address, adds fffe into the middle of it. Then it takes the first 8 bits, converts them into binary, flips the value of the 7th bit, and that's it.

  • e.g. MAC address 00608c123abc becomes 02608cfffe123abc, which is expressed as 260:8cff:fe12:eabc

To prevent unauthorized monitoring of a specific interface using it's identifiers, a technique called Privacy Extensions was developed. Privacy Extensions use pseudorandom numbers as it's interface ID, called a temporary token.

Linklocal addresses aren't forwarded by routers, and only span a single subnet. Nodes on the same link are neighbors. The range for linklocal addressing is fe80::/10. All linklocal addresses start with a leading fe80, followed by 54 bits of zeros, and the final 64 bits are the Interface ID.

The equivalent of a linklocal address would by an address assigned by Automatic-Private-IP-Addressing, but unlike IPv4, all IPv6 hosts get a linklocal address, even if they have a globally unique one assigned by DHCPv6.

Linklocal addresses also have something called a zone index, (%1 for Windows, %eth0 for Linux) which differentiates between the different links a host can have. For example, even if an IPv6 host has a loopback address, an Ethernet address, and a VPN address, they all use the same linklocal address. Zone indexes help identify the source of the address.

Multicast Addressing

In order to use multicast on an IPv6 network, all the routers in said network must support IPv6 multicasting.

  • first 8 bits are the multicast indicator
  • next 4 bits are multicast flag
  • next 4 bits are the scope (1 for node-local, 2 for link-local)
  • final 112 bits are the multicast groups for the scope

Nodes can join multicast groups using Multicast Listener Discovery, and can also discover other group members that are a part of the local subnet. General node discovery is done using the Neighbor Discovery (ND) protocol, the IPv4 equivalent of ARP. Since broadcast addresses are inefficient, they aren't implemented in IPv6. Nodes will use an appropriate multicast address instead.

Unicast addresses in IPv6 are configured with a second address, called a solicited-node multicast address. This is the address used by ND to resolve addresses. It reduces the number of hosts that are likely to receive ND messages, making it much more efficient than ARP.

#Netplus

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