1. Neighbor Discovery

2. IPv6 Terminology Additional subnets Router Host Neighbors Host Intra-subnet router Switch LAN segment Link Subnet Network

3. Neighbor Discovery Overview Set of messages and processes that determine relationships between neighboring nodes –Replaces ARP, ICMPv4 Router Discovery, and ICMPv4 Redirect ND is used by nodes: –For address resolution –To determine link-layer address changes –To determine neighbor reachability ND is used by hosts: –To discover neighboring routers –Autoconfigure addresses, address prefixes, and other configuration parameters ND is used by routers: –To advertise their presence, host configuration parameters, and on-link prefixes –To inform hosts of a better next-hop address to forward packets for a specific destination

4. Neighbor Discovery Processes Router discovery Prefix discovery Parameter discovery Address autoconfiguration Address resolution Next-hop determination Neighbor unreachability detection Duplicate address detection Redirect function

5. Neighbor Discovery Message Format ICMPv6 message structure and ICMPv6 types 133 through 137 To ensure local link traffic, all ND messages are sent with a hop limit of 255 IPv6 Header Next Header = 58 (ICMPv6) Neighbor Discovery Message Options Neighbor Discovery Message Header Neighbor Discovery Message

6. Neighbor Discovery Options Type 1: Source Link-Layer Address Type 2: Target Link-Layer Address Type 3: Prefix Information Type 4: Redirected Header Type 5: MTU Type 7: Advertisement Interval Type 8: Home Agent Information Type 9: Route Information

7. Mapping IPv6 Multicast Addresses to Ethernet Addresses IPv6 Multicast Address 33-33- 81624 32 FF...: Ethernet Multicast Address

8. Neighbor Discovery Messages Router Solicitation Router Advertisement Neighbor Solicitation Neighbor Advertisement Redirect

9. Structure of the Router Solicitation Message Type Code Checksum Reserved Options = 133 = 0...

10. Router Solicitation message The Router Solicitation message is sent by IPv6 hosts to discover the presence of IPv6 routers on the link. A host sends a multicast Router Solicitation message to prompt IPv6 routers to respond immediately, rather than waiting for an unsolicited Router Advertisement message For example, assuming that the local link is Ethernet, in the Ethernet header of the Router Solicitation message you will find these settings: The Source Address field is set to the MAC address of the sending network adapter. The Destination Address field is set to 33-33-00-00-00-02.

11. Router Solicitation message For example, assuming that the local link is Ethernet, in the Ethernet header of the Router Solicitation message you will find these settings: The Source Address: MAC address of the sending network adapter. The Destination Address: 33-33-00-00-00-02.(which is the Ethernet MAC address corresponding to the link-local scope all-nodes multicast address.)

12. Router Solicitation message In the IPv6 header of the Router Solicitation message ■ The Source Address field is set to either a link-local IPv6 address assigned to the sending interface or the IPv6 unspecified address (::). ■ The Destination Address field is set to the link-local scope all-routers multicast address (FF02::2).

13. Router Solicitation message Source Link-Layer Address option When present, the Source Link-Layer Address option contains the link-layer address of the sender. For an Ethernet node, the Source Link-Layer Address option contains the Ethernet MAC address of the sending host. The address in the Source Link-Layer Address option is used by the receiving router to determine the unicast MAC address of the host to which the corresponding unicast Router Advertisement is sent.

14. Router Advertisement Message Type Code Checksum Current Hop Limit Managed Address Configuration flag Other Stateful Configuration flag Home Agent flag Default Router Preference Reserved Router Lifetime Reachable Time Retrans Timer Options = 134 = 0...

15. Router Advertisement Message Router Advertisement messages in response to the receipt of a Router Solicitation message. The Router Advertisement message contains the information required by hosts to determine the link prefixes, the link MTU, specific routes, whether or not to use address autoconfiguration, and the duration for which addresses created through address autoconfiguration are valid and preferred.

16. Router Advertisement Message For example, assuming that the local link is Ethernet, in the Ethernet header of the Router Advertisement message, you will find these settings: ■ The Source Address field is set to the MAC address of the sending network adapter. ■ The Destination Address field is set to either 33-33-00- 00-00-01 or the unicast MAC address of the host that sent a Router Solicitation from a unicast address..

17. Router Advertisement Message In the IPv6 header of the Router Advertisement message, you will find the following settings: ■ The Source Address field is set to the link-local address assigned to the sending interface. ■ The Destination Address field is set to either the link- local scope all-nodes multicast address (FF02::1) or the unicast IPv6 address of the host that sent the Router Solicitation message from a unicast address. ■ The Hop Limit field is set to 255.

18. Router Discovery Nodes discover the set of routers on the local link IPv6 router discovery also provides: –Default value of Hop Limit field –Use of stateful address protocol –Reachability and retransmission timers –Network prefixes for the link –MTU of the local link –IPv6 mobility information –Routes

19. Multicast Router Solicitation Message Router Host A  Send multicast Router Solicitation Router Solicitation Ethernet Header Destination MAC is 33-33-00-00-00-02 IPv6 Header Source Address is :: Destination Address is FF02::2 Hop limit is 255 Router Solicitation Header MAC: 00-B0-D0-E9-41-43 IP: none MAC: 00-10-FF-D6-58-C0 IP: FE80::210:FFFF:FED6:58C0

20. Multicast Router Advertisement Message Host A Ethernet Header Destination MAC is 33-33-00-00-00-01 IPv6 Header Source Address is FE80::210:FFFF:FED6:58C0 Destination Address is FF02::1 Hop limit is 255 Router Advertisement Header Current Hop Limit, Flags, Router Lifetime, Reachable and Retransmission Timers Neighbor Discovery Options Source Link-Layer Address is 00-10-FF-D6-58-C0 MTU is 1500 Prefix Information is for FEC0:0:0:F282::/64 MAC: 00-10-FF-D6-58-C0 IP: FE80::210:FFFF:FED6:58C0 Router ‚ Send multicast Router Advertisement Router Advertisement MAC: 00-B0-D0-E9-41-43 IP: none

21. Structure of the Neighbor Solicitation Message Type Code Checksum Reserved Target Address Options = 135 = 0...

22. Neighbor Solicitation Message IPv6 nodes send the Neighbor Solicitation message to discover the link-layer address of an on-link IPv6 node. It typically includes the link-layer address of the sender. Typical Neighbor Solicitation messages are multicast for address resolution and unicast when the reachability of a neighboring node is being verified

23. Neighbor Solicitation Message For example, assuming that the local link is Ethernet, in the Ethernet header of the Neighbor Solicitation message, you will find the following settings: ■ The Source Address field is set to the MAC address of the sending network adapter. ■ For a multicast Neighbor Solicitation message, the Destination Address field is set to the Ethernet MAC address that corresponds to the solicited-node address of the target. ■ For a unicast Neighbor Solicitation message, the Destination Address field is set to the unicast MAC address of the neighbor

24. Neighbor Solicitation Message In the IPv6 header of the Neighbor Solicitation message, you will find these settings: ■ The Source Address field is set to either a unicast IPv6 address assigned to the sending interface or, during duplicate address detection, the unspecified address (::). ■ For a multicast Neighbor Solicitation, the Destination Address field is set to the solicited node address of the target. ■ For a unicast Neighbor Solicitation, the Destination Address field is set to the unicast address of the target. ■ The Hop Limit field is set to 255.

25. Neighbor Solicitation Message Source Link-Layer Address option When present, the Source Link-Layer Address option contains the link- layer address of the sender. For an Ethernet node, the Source Link-Layer Address option contains the Ethernet MAC address of the sending node. The receiving node uses the address in the Source Link- Layer Address option to determine the unicast MAC address of the node to which the corresponding Neighbor Advertisement

26. Neighbor Solicitation Message Example + Frame: Base frame properties ETHERNET: ETYPE = 0x86DD : Protocol = Unknown + ETHERNET: Destination address : 3333FF026EA5 + ETHERNET: Source address : 00105AAA20A2 ETHERNET: Frame Length : 86 (0x0056) ETHERNET: Ethernet Type : 0x86DD ETHERNET: Ethernet Data: Number of data bytes remaining = 72 (0x0048) IP6: Proto = ICMP6; Len = 32 IP6: Version = 6 (0x6) IP6: Traffic Class = 0 (0x0) IP6: Flow Label = 0 (0x0) IP6: Payload Length = 32 (0x20) IP6: Next Header = 58 (ICMP6) IP6: Hop Limit = 255 (0xFF) IP6: Source Address = fe80::210:5aff:feaa:20a2 IP6: Destination Address = ff02::1:ff02:6ea5 IP6: Payload: Number of data bytes remaining = 32 (0x0020) ICMP6: Neighbor Solicitation; Target = fe80::260:97ff:fe02:6ea5 ICMP6: Checksum = 0x0F35 ICMP6: Type = 135 (Neighbor Solicitation) ICMP6: Code = 0 (0x0) ICMP6: Reserved ICMP6: Target Address = fe80::260:97ff:fe02:6ea5 ICMP6: Source Link-level Address = 00 10 5A AA 20 A2 ICMP6: Type = 1 (0x1) ICMP6: Length = 1 (0x1) ICMP6: Source Link-level Address = 00 10 5A AA 20 A2 + Frame: Base frame properties ETHERNET: ETYPE = 0x86DD : Protocol = Unknown + ETHERNET: Destination address : 3333FF026EA5 + ETHERNET: Source address : 00105AAA20A2 ETHERNET: Frame Length : 86 (0x0056) ETHERNET: Ethernet Type : 0x86DD ETHERNET: Ethernet Data: Number of data bytes remaining = 72 (0x0048) IP6: Proto = ICMP6; Len = 32 IP6: Version = 6 (0x6) IP6: Traffic Class = 0 (0x0) IP6: Flow Label = 0 (0x0) IP6: Payload Length = 32 (0x20) IP6: Next Header = 58 (ICMP6) IP6: Hop Limit = 255 (0xFF) IP6: Source Address = fe80::210:5aff:feaa:20a2 IP6: Destination Address = ff02::1:ff02:6ea5 IP6: Payload: Number of data bytes remaining = 32 (0x0020) ICMP6: Neighbor Solicitation; Target = fe80::260:97ff:fe02:6ea5 ICMP6: Checksum = 0x0F35 ICMP6: Type = 135 (Neighbor Solicitation) ICMP6: Code = 0 (0x0) ICMP6: Reserved ICMP6: Target Address = fe80::260:97ff:fe02:6ea5 ICMP6: Source Link-level Address = 00 10 5A AA 20 A2 ICMP6: Type = 1 (0x1) ICMP6: Length = 1 (0x1) ICMP6: Source Link-level Address = 00 10 5A AA 20 A2

27. Neighbor Advertisement Message An IPv6 node sends the Neighbor Advertisement message in response to a Neighbor Solicitation message An IPv6 node also sends unsolicited Neighbor Advertisements to inform neighboring nodes of changes in link-layer addresses or the node’s role.

28. Neighbor Advertisement Message For example, assuming that the local link is Ethernet, in the Ethernet header of the Neighbor Advertisement message, you will find the following settings: ■ The Source Address field is set to the MAC address of the sending network adapter. ■ The Destination Address field is set, For a solicited Neighbor Advertisement, to the unicast MAC address of the initial Neighbor Solicitation sender. ■ For an unsolicited Neighbor Advertisement, the Destination Address field is set to 33-33-00-00-00-01, which is the Ethernet MAC address corresponding to the link-local scope all-nodes multicast address.

29. Neighbor Advertisement Message In the IPv6 header of the Neighbor Advertisement message, you will find these settings: ■ The Source Address field is set to a unicast address assigned to the sending interface. ■ The Destination Address field is set, for a solicited Neighbor Advertisement, to the unicast IP address of the sender of the initial Neighbor Solicitation. For an unsolicited Neighbor Advertisement, the Destination Address field is set to the link-local scope all-nodes multicast address (FF02::1). ■ The Hop Limit field is set to 255..

30. Summary of ND Messages and Options ND MessageND Option(s) Router SolicitationSource Link-Layer Address Router AdvertisementSource Link-Layer Address Prefix Information MTU Advertisement Interval Home Agent Information Route Information Neighbor SolicitationSource Link-Layer Address Neighbor AdvertisementTarget Link-Layer Address RedirectRedirected Header Target Link-Layer Address

31. Neighbor Discovery Processes ND provides message exchanges for the following processes: –Address resolution (including duplicate address detection) –Router discovery (including prefix and parameter discovery) –Neighbor unreachability detection –Redirect function

32. Address Resolution Process An exchange of Neighbor Solicitation and Neighbor Advertisement messages to resolve the link-layer address of the next- hop address –Multicast Neighbor Solicitation message –Unicast Neighbor Advertisement message Both hosts update their neighbor caches Unicast traffic can now be sent

33. Multicast Neighbor Solicitation Host B Host A  Send multicast Neighbor Solicitation Neighbor Solicitation Ethernet Header Destination MAC is 33-33-FF-02-6E-A5 IPv6 Header Source Address is FE80::210:5AFF:FEAA:20A2 Destination Address is FF02::1:FF02:6EA5 Hop limit is 255 Neighbor Solicitation Header Target Address is FE80::260:97FF:FE02:6EA5 Neighbor Discovery Option Source Link-Layer Address is 00-10-5A-AA-20-A2 MAC: 00-10-5A-AA-20-A2 IP: FE80::210:5AFF:FEAA:20A2 MAC: 00-60-97-02-6E-A5 IP: FE80::260:97FF:FE02:6EA5

34. Unicast Neighbor Advertisement Host B Host A ‚ Send unicast Neighbor Advertisement Neighbor Advertisement Ethernet Header Destination MAC is 00-10-5A-AA-20-A2 IPv6 Header Source Address is FE80::260:97FF:FE02:6EA5 Destination Address is FE80::210:5AFF:FEAA:20A2 Hop limit is 255 Neighbor Advertisement Header Target Address is FE80::260:97FF:FE02:6EA5 Neighbor Discovery Option Target Link-Layer Address is 00-60-97-02-6E-A5 MAC: 00-10-5A-AA-20-A2 IP: FE80::210:5AFF:FEAA:20A2 MAC: 00-60-97-02-6E-A5 IP: FE80::260:97FF:FE02:6EA5

35. Neighbor Unreachability Detection A neighboring node is reachable if: –There has been a recent confirmation that IPv6 packets sent were received and processed by the neighboring node Detects whether the first hop to the destination is reachable Reachability is determined by: –Receipt of a Neighbor Advertisement message in response to a unicast Neighbor Solicitation message –Upper layer protocol indicators

36. Duplicate Address Detection Use of a neighbor solicitation to detect a duplicate unicast address –Target Address field in the Neighbor Solicitation message is set to the IPv6 address for which duplication is being detected –The Source Address is set to the unspecified address (::) For a duplicate address, the defending node replies with a multicast Neighbor Advertisement –The Destination Address is set to the link-local scope all-nodes multicast address (FF02::1)

37. Multicast Neighbor Solicitation for Duplicate Address Detection Host B Host A  Send multicast Neighbor Solicitation Neighbor Solicitation Tentative IP: FEC0::2:260:8FF:FE52:F9D8 MAC: 00-60-08-52-F9-D8 IP: FEC0::2:260:8FF:FE52:F9D8 Ethernet Header Dest MAC is 33-33-FF-52-F9-D8 IPv6 Header Source Address is :: Destination Address is FF02::1:FF52:F9D8 Hop limit is 255 Neighbor Solicitation Header Target Address is FEC0::2:260:8FF:FE52:F9D8

38. Multicast Neighbor Advertisement for a Duplicate Address Host B Host A Ethernet Header Destination MAC is 33-33-00-00-00-01 IPv6 Header Source Address is FEC0::2:260:8FF:FE52:F9D8 Destination Address is FF02::1 Hop limit is 255 Neighbor Advertisement Header Target Address is FEC0::2:260:8FF:FE52:F9D8 Neighbor Discovery Option Target Link-Layer Address is 00-60-08-52-F9-D8 Tentative IP: FEC0::2:260:8FF:FE52:F9D8 ‚ Send multicast Neighbor Advertisement Neighbor Advertisement MAC: 00-60-08-52-F9-D8 IP: FEC0::2:260:8FF:FE52:F9D8

39. Router Discovery Nodes discover the set of routers on the local link IPv6 router discovery also provides: –Default value of Hop Limit field –Use of stateful address protocol –Reachability and retransmission timers –Network prefixes for the link –MTU of the local link –IPv6 mobility information –Routes

40. Multicast Router Solicitation Message Router Host A  Send multicast Router Solicitation Router Solicitation Ethernet Header Destination MAC is 33-33-00-00-00-02 IPv6 Header Source Address is :: Destination Address is FF02::2 Hop limit is 255 Router Solicitation Header MAC: 00-B0-D0-E9-41-43 IP: none MAC: 00-10-FF-D6-58-C0 IP: FE80::210:FFFF:FED6:58C0

41. Multicast Router Advertisement Message Host A Ethernet Header Destination MAC is 33-33-00-00-00-01 IPv6 Header Source Address is FE80::210:FFFF:FED6:58C0 Destination Address is FF02::1 Hop limit is 255 Router Advertisement Header Current Hop Limit, Flags, Router Lifetime, Reachable and Retransmission Timers Neighbor Discovery Options Source Link-Layer Address is 00-10-FF-D6-58-C0 MTU is 1500 Prefix Information is for FEC0:0:0:F282::/64 MAC: 00-10-FF-D6-58-C0 IP: FE80::210:FFFF:FED6:58C0 Router ‚ Send multicast Router Advertisement Router Advertisement MAC: 00-B0-D0-E9-41-43 IP: none

42. Redirect Function Inform originating hosts of a better first-hop neighbor to which traffic should be forwarded for a specific destination Two instances: 1. A router informs an originating host of the IP address of a router available on the local link that is “closer” to the destination 2. A router informs an originating host that the destination is a neighbor (it is on the same link as the originating host) Redirect message contains best first-hop address information Redirect messages are only sent by the first router in the path between the originating host and the destination

43. IPv4 Neighbor Functions and IPv6 Equivalents IPv4 Neighbor FunctionIPv6 Neighbor Function ARP Request messageNeighbor Solicitation message ARP Reply messageNeighbor Advertisement message ARP cacheNeighbor cache Gratuitous ARPDuplicate address detection Router Solicitation message (optional)Router Solicitation (required) Router Advertisement message (optional)Router Advertisement (required)Redirect message

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