IPv6 Link Local address is one of the most confusing topic in the world of IPv6.
Because there is no equivalent address in the world of IPv4. The question that arises is what are the benefits of this Link Local Address?
Link-Local address are used on infrastructure links between routers in an IPv6 network. Links between routers are called Infrastructure Links per RFC 7404. LLA is used for communication and connectivity in that link. LLA are not advertised by routing protocols and not present in the routing table.
As we know routing protocols in IPv6 use Link Local Address to exchange routing informations and as the next hop for each learned route in the routing table.
The consequence of this new routing behavior in IPv6 is that we can route using Link-Local Address only and we do not require Global Unicast Address under each link between routers, this reduces the size of the routing tables.
RFC 7404 lists a number of interesting advantages using only Link-Local Addresses in IPv6 network :
Less routing table entries - Since the routing protocol does not advertise link-local addresses, it means that infrastructure links won't be presented in the routing table. This reduces memory consumption and increases the convergence speed of the routing protocol.
Better address management - Only one GUA loopback address per router is required to have all IPv6 services up and running. This means simpler and more efficient address management comparing to IPv4.
More secure links - Every global unicast address on a router is a potential attack point for DDOS and other attacks. Using only link-local addresses on infrastructure links means that the links are not reachable remotely and do not need to be protected from outside the network.
