What is true about a link-local address (fe80::/10)?

It is valid only on a single link and is never forwarded by routers

Routers forward it across the Internet

In an IPv6 multicast address ff02::1, what does the digit 2 represent?

Flags value for permanent group

Which describes the global unicast address 2001:db8:1234:1::10/64?

Prefix 2000::/3, routable on the whole Internet, one-to-one

Prefix fe80::/10, valid on one link

Prefix fec0::/10, one site only

Why must the outgoing interface be named with a link-local address, such as fe80::1%eth0?

Because the same fe80::1 may exist on many links

Because it is longer than other addresses

Because link-local is routed globally

Because it replaces the MAC address

2074 Magh · 10 marks

Global unicast, link local, site local, multicast

Short answer

Global unicast (2000::/3) is globally routable, e.g. 2001:db8:1234:1::10. Link-local (fe80::/10) works only on one link, e.g. fe80::21a:2bff:fe3c:4d5e. Site-local (fec0::/10) is deprecated, replaced by unique local fc00::/7. Multicast (ff00::/8) delivers to a group, e.g. ff02::1.

Explain Global Unicast, Link Local, Site local and Multicast address with examples and its scope.

IPv6 addresses are 128-bit. The kind of address and its scope are decided by the leading bits (prefix).

Type	Prefix	Scope	Example
Global unicast	2000::/3	Whole Internet	2001:db8:1234:1::10
Link-local	fe80::/10	Single link only	fe80::21a:2bff:fe3c:4d5e
Site-local (deprecated)	fec0::/10	One site	fec0:0:0:1::5
Multicast	ff00::/8	Depends on scope field	ff02::1

Global unicast

Globally routable, unique one-to-one address, like a public IPv4 address. Structure: 48-bit global routing prefix (given by the ISP), 16-bit subnet ID, 64-bit interface ID. Example: 2001:db8:1234:1::10/64. Scope: global; packets can cross the Internet. (2001:db8::/32 is reserved for documentation.)

Link-local

Automatically created on every IPv6 interface from prefix fe80::/10 and the interface ID (usually EUI-64 or random). It is valid only on the local link, and routers never forward packets with link-local source or destination. Used for neighbour discovery, router advertisements and routing protocol next hops. Example: fe80::21a:2bff:fe3c:4d5e. Scope: one link/subnet.

Site-local

Prefix fec0::/10, meant for private addressing inside one site, similar to IPv4 private ranges (10.x). Because of ambiguity between sites it was deprecated by RFC 3879 and replaced by Unique Local Addresses (fc00::/7, usually fd00::/8), for example fd12:3456:789a:1::1. Scope: one site or organisation, not routed on the global Internet.

Multicast

Identifies a group of interfaces; a packet is delivered to every member. It replaces broadcast. Format: ff + flags (4 bits) + scope (4 bits) + group ID.

Scope value	Scope
1	Interface-local
2	Link-local
5	Site-local
8	Organisation-local
e	Global

Examples: ff02::1 all nodes on the link, ff02::2 all routers on the link, ff02::5 all OSPF routers, ff05::2 all routers in the site, ff0e:: global scope groups.

Quick comparison of scope

 Interface-local (::1)  <  Link-local (fe80::)
        <  Site / Unique local (fd00::)
        <  Global unicast (2xxx::)

A link-local address is not unique across links; the same fe80::1 may exist on many links, so the outgoing interface must be named (e.g. fe80::1%eth0).
Global unicast and unique local addresses are unique to a site or the world and are normally given to hosts by SLAAC, DHCPv6 or manual configuration.
Every IPv6 interface normally has several addresses at once: one link-local, one or more global, and the multicast groups ff02::1 and the solicited-node group ff02::1:ffxx:xxxx.

✓ Answer checked by Claude Opus 5.5 (high effort)

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