IPv6 routers have exactly the same problem as IPv4 routers when receiving IP packets for delivery on the link: the IP address of a terminal on the link must be resolved to a local link layer address. The IPv6 routers solve the problem in roughly the same way as IPv4 routers do: the router sends out a query to all terminals on the link requesting a mapping, and the terminal owning the IP address responds with its link address. The details, however, are quite different.
Instead of using a link layer protocol, the Neighbor Discovery protocol species a set of IP layer messages: Neighbor Solicitation (NS) and Neighbor Advertisement (NA).
The NS message is multicast out by the router to a multicast address to which all terminals on the link are listening. The NS message contains the IPv6 address of the packet which the router would like to deliver. The receiving terminal checks the IP address congured on the receiving network interface, and replies to the router with an NA containing the IP address to link address mapping if the receiving network interface is congured with the queried address. Upon receiving the NA, the router can deliver the packet. As in IPv4, terminals can also use address resolution between themselves to determine if another terminal is on link, and thereby avoid having to route packets through the access router.
Neighbor Discovery utilizes the router discovery and address resolution mechanism to allow autoconguration of addresses. Each terminal must autocongure at least one address: a link local IPv6 address that is only routed up to the access router, i.e. only among terminals and access routers in the local IP subnet. Link local addresses are not distributed using DHCP. Depending on the access network deployment, terminals may also autocongure globally routable IP addresses for access to the Internet, or they may use DHCP to obtain globally routable addresses. Which procedure to use is indicated in the RAs a terminal receives from the access routers when the terminal rst arrives on the local link. The advantage of autocon?guration is that it removes the cost and effort of managing a DHCP server for address conguration, though DHCP may be required for obtaining other information, such as the DNS conguration.
IPv6 routers have exactly the same problem as IPv4 routers when receiving IP packets for delivery on the link: the IP address of a terminal on the link must be resolved to a local link layer address. The IPv6 routers solve the problem in roughly the same way as IPv4 routers do: the router sends out a query to all terminals on the link requesting a mapping, and the terminal owning the IP address responds with its link address. The details, however, are quite different.
Instead of using a link layer protocol, the Neighbor Discovery protocol species a set of IP layer messages: Neighbor Solicitation (NS) and Neighbor Advertisement (NA).
The NS message is multicast out by the router to a multicast address to which all terminals on the link are listening. The NS message contains the IPv6 address of the packet which the router would like to deliver. The receiving terminal checks the IP address congured on the receiving network interface, and replies to the router with an NA containing the IP address to link address mapping if the receiving network interface is congured with the queried address. Upon receiving the NA, the router can deliver the packet. As in IPv4, terminals can also use address resolution between themselves to determine if another terminal is on link, and thereby avoid having to route packets through the access router.
Neighbor Discovery utilizes the router discovery and address resolution mechanism to allow autoconguration of addresses. Each terminal must autocongure at least one address: a link local IPv6 address that is only routed up to the access router, i.e. only among terminals and access routers in the local IP subnet. Link local addresses are not distributed using DHCP. Depending on the access network deployment, terminals may also autocongure globally routable IP addresses for access to the Internet, or they may use DHCP to obtain globally routable addresses. Which procedure to use is indicated in the RAs a terminal receives from the access routers when the terminal rst arrives on the local link. The advantage of autocon?guration is that it removes the cost and effort of managing a DHCP server for address conguration, though DHCP may be required for obtaining other information, such as the DNS conguration.
access point vs router
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