IPv6 Neighbor Discovery replaces ARP and ICMP redirection in IPv4 to determine relationships between neighboring nodes. It has functions for host-router discovery like router solicitation, prefix discovery, and parameter discovery. Neighbor Discovery also has functions for host-to-host communication like address resolution, next hop determination, neighbor unreachability detection, and duplicate address detection.

1. IPv6 Neighbour Discovery by R Radhakrishnan KRISHNA INSTITUTE OF ENGINEERING AND TECHNOLOGY

2. IPv6 Neighbour Discovery IPv6 Neighbor Discovery (ND) is a set of messages and processes that determine relationships between neighboring nodes. ND replaces ARP, ICMP Router Discovery, and ICMP Redirect used in IPv4 and provides additional functionality

3. Functions of ND

4. Functions of ND The Neighbor Discovery protocol has nine individual functions, many of which are related to each other. They are organized into three functional groups: host-router discovery functions host-host communication functions the redirect function.

5. Host-Router Discovery Functions Facilitate the discovery of local routers and the exchange of information between them and hosts. This includes four specific functions: 1. Router Discovery: This is the core function of this group: the method by which hosts locate routers on their local network 2. Prefix Discovery: Hosts use this function to determine what network they are on, which in turn tells them how to differentiate between local and distant destinations and whether to attempt direct or indirect delivery of datagrams

6. Host-Router Discovery Functions 3. Parameter Discovery: A function by which a host learns important parameters about the local network and/or routers, such as the MTU of the local link. 4. Address Autoconfiguration: Hosts in IPv6 are designed to be able to automatically configure themselves, but this requires information that is normally provided by a router.

7. Host-Host Communication Functions 1. Address Resolution: A device determines the L2 address of another device on the local network from that device's L3 address. Equivalent to ARP in IPv4. 2. Next-Hop Determination: The method for looking at an IP datagram's destination address and determining where it should next be sent. 3. Neighbor Unreachability Detection: The process of determining whether or not a neighbor device can be directly contacted. 4. Duplicate Address Detection: Determining if an address that a device wishes to use already exists on the network.

8. Redirection 1. Redirect Function : A technique whereby a router informs a host of a better next-hop node to use for a particular destination

9. ICMPv6 Messages Used By the NDP Router Advertisement Messages: Sent regularly by routers to tell hosts that they exist and provide important prefix and parameter information to them. Router Solicitation Messages: Sent by hosts to request that any local routers send a Router Advertisement message. Neighbor Advertisement Messages: Sent by hosts to indicate the existence of the host and provide information about it. Neighbor Solicitation Messages: Sent to verify the existence of another host and to ask it to transmit a Neighbor Advertisement. Redirect Messages: Sent by a router to tell a host of a better method to route data to a particular destination.

10. Router Solicitation Type = 133 Code = 0 Checksum Reserved Possible option: Source Link Layer Address

11. Router Advertisement Type = 134 Code = 0 Checksum Cur. Hop Limit M O Reserved Router Lifetime Reachable Time Retransmission Timer Possible options: -Source Link Layer Address MTU Prefix Information

12. Neighbor Solicitation Type = 135 Code = 0 Checksum Reserved Target Address Possible option: Source Link Layer Address

13. Neighbor Advertisment Type = 136 Code = 0 Checksum R S O Reserved Target Address Possible option: Source Link Layer Address

14. Prefix Option Type Length Prefix Length L A Reserved Valid Lifetime Preferred Lifetime Reserved Prefix List

15. What is AR ? Communication On an internetwork is done by sending data at layer three using a N/W layer address. The actual transmission of data occurs at layer two using a DLL address. It is necessary to define some way of being able to link these two addresses. This is done by taking a network layer address and determining what DLL address goes with it, this process is called address resolution.

16. Why addressing is done at two different layers? As they are very different types of addresses those are used for diff. Purposes. Layer two addresses(IEEE 802 MAC addresses)are used for local transmission b/w h/w devices that can communicate directly. In contrast layer three addresses(IP addresses) are used in internetworking.

17. Why AR is necessary? If a client on the local n/w is accessing a server somewhere on the internet. Logically this connection can be made directly b/w the client and server. But in reality is a sequence of physical links at layer two. At each step the decision of where to send the data is made based on a layer three address. But the actual transmission must be performed using layer two address.

18. Dynamic Address Resolution Dynamic address resolution is usually implemented using a special protocol. A device that knows only the n/w layer address of another device can use this protocol to request the other device’s h/w address.

19. LAN Switch Device C IP address: IPC H/W address: #46 Device A IP address: IPA H/W address: #43 Device B IP address: IPB H/W address: #79 Device D IP address: IPD H/W address: #48 Who is IPB? IPB is #79

20. Dynamic Address Resolution(Contd.) In the previous device A has to send the data to device B but knows only its IP address (“IPB”),and not its H/W address. A broadcast request asking to be send to the H/W address of the device using the IP address “IPB”.B responds back to A directly with the H/W address.

21. About ARP ARP is a relatively simple request/reply protocol.The source device broadcasts an ARP request looking for a particular device based on it IP address.The device responds with its h/w address in an ARP reply message.

22. Solicited-Node Address

23. Solicited-node multicast address from link local address A Node with link-local address of FE80::2AA:FF:FE 28:9C5A also listens on the corresponding solicited-node multicast address of FF02::1:FF 28:9C5A

24. AR in IPv6 Address resolution in IPv6 uses the new Neighbor Discovery (ND) protocol instead of the Address Resolution Protocol. A device trying to send an IPv6 datagram sends a Neighbor Solicitation message to get the address of another device The device responds with a Neighbor Advertisement . The request is sent using a solicited-node multicast address rather than broadcast, to improve efficiency.

25. AR in IPv6 Host A MAC address: 00-AA-00-11-11-11 Link-local address of FE80::2AA:FF:FE11:1111. Host B MAC address: 00-AA-00-22-22-22 Link-local address: FE80::2AA:FF:FE22:2222. To send a packet to Host B, Host A must use address resolution to resolve Host B’s link-layer address. Based on Host B’s IP address, Host A sends a solicited-node multicast Neighbor Solicitation to the IP address :-FF02::1:FF22:2222 and MAC address 33-33-FF-22-22-22

27. Processing by Node B Host B, having registered the solicited-node multicast address of 33-33-FF-22-22-22 with its Ethernet adapter, receives and processes the Neighbor Solicitation. Host B responds with a unicast Neighbor Advertisement message

29. lifetimes for an autoconfigured address

30. Auto configuration process A tentative link-local address is derived based on the link-local prefix of FE80::/64 and the 64-bit interface identifier. Using duplicate address detection to verify the uniqueness of the tentative link-local address Neighbor Solicitation message is sent with the Target Address field that is set to the tentative link-local address

31. Auto configuration process If a Neighbor Advertisement message sent in response to the Neighbor Solicitation message is received, this indicates that another node on the local link is using the tentative link-local address and address autoconfiguration stops. At this point, manual configuration must be performed on the node

32. Auto configuration process If no Neighbor Advertisement message is received, the tentative link-local address is assumed to be unique and valid. The link-local address is initialized for the interface. The corresponding solicited-node multicast link-layer address is registered with the network adapter.

33. Auto address continues The host sends up to 3 Router Solicitation messages (by default). If no Router Advertisement messages are received, then the host uses a stateful address configuration protocol to obtain addresses and other configuration parameters. If a Router Advertisement message is received, the Hop Limit, Reachable Time, Retrans Timer, and the MTU (if the MTU option is present) are set. Uniqueness determined for each prefix

34. Address auto-configuration Avoids Manual configuration of individual machines before connecting them to the network. Address auto-configuration assumes that each interface has an unique ID Plug-and-play communication is achieved through the use of link-local addresses Small sites should not need stateful servers A large site with multiple networks and routers should not require the presence of a stateful address configuration server. Address configuration should facilitate the graceful renumbering of a site's machines

35. Stateless Autoconfiguration Generate a link local address Verify this tentative address is OK. Use a neighbor solicitation with the tentative address as the target. ICMP type 135 If the address is in use a neighbor advertisement message will be returned. ICMP type 136 If no response, assign the address to the interface. At this point the node can communicate on-link. Fail and go to manual configuration or choose a different interface token.

36. Stateless Autoconfiguration Assign address to interface. Node joins the All Routers multicast group. FF02::1 Sends out a router solicitation message to that group. ICMP type 133 Router responds with a router advertisement. ICMP type 134

37. Stateless Autoconfiguration Look at the “managed address configuration" flag If M = 0 proceed with stateless configuration If M = 1 stop and do stateful config Look at "other stateful configuration" flag If O = 0 finish If O = 1 use stateful configuration for other information

38. Stateless Autoconfig Routers are to send out router advertisements at regular intervals to the all-hosts address. This should update lifetimes. Note that stateless autoconfig will only configure addresses. It will not do all the host configuration you may well want to do. RFC 2462 defines IPv6 Stateless Autoconfig