packet sent to multicast address is delivered to all receivers of the multicast address (see more in Section 3.2.4). Notably, IPv6 does not have a concept of broadcast like IPv4. The multicast address type can be used to implement all broadcast use cases. The address of all zeros, : :, is called the unspecified address. The unspecified address is used to indicate a lack of address. This address is never used as a destination. It's only use as a source address takes place during initial source address configuration (see Section 3.4.7). 3.1.3 IPv6 Address Scopes The concept of address scopes is inbuilt in IPv6, as described by RFC 4007 [5]. The unspecified address, : has no scope. Addresses with link-local scope can be used only for communication within a single link, even when the link has no routers on it. Every network interface, with few exceptions, automatically creates a link-local address (see more in Section 3.5.1). A special case of link-local scope is the loopback address, : 1, which is considered to be an address in virtual interface inside a node, even if the address does not have the link-local prefix. Figure 3.2 illustrates how a link-local address is constructed: the first 10 bits are fe80, the following 54 bits are all zeros, and the last 64 bits contain an IID. The link-local addresses are useful for communications that are intended to stay on a link, and in cases where routers are not present or global addresses are not (yet) configured for a host. The other major address scope used in IPv6 is global scope; addresses of global scope can be used for local or global - off-link - communications. IPv6 used to have the concept 10 bits 54 bits 64 bits Interface Identifier (IID) 1111 1110 10 fe80::/10 Figure 3.2 IPv6 link-local address format. Deploying IPv6 in 3GPP Networks 7 bits 40 bits 16 bits 64 bits 1111 110 global ID subnet ID Interface Identifier (IID) 1 is locally assigned 0 is globally assigned Figure 3.3 Generic IPv6 Unique Local Address format. of site-local scope, but that was deprecated by 