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IPv6: Neighbor Discovery

IPv6: Neighbor Discovery. Billy Bian SW2 Great China R&D Center ZyXEL Communications, Inc. Outline:. N eighbor D iscovery (ND) Overview Neighbor Discovery Message Format Neighbor Discovery Processes Conceptual Host Data Structures Host Sending Algorithm Appendix Q&A.

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IPv6: Neighbor Discovery

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  1. IPv6: Neighbor Discovery Billy Bian SW2 Great China R&D Center ZyXEL Communications, Inc

  2. Outline: • Neighbor Discovery (ND) Overview • Neighbor Discovery Message Format • Neighbor Discovery Processes • Conceptual Host Data Structures • Host Sending Algorithm • Appendix • Q&A

  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

  4. ND is used by hosts: • To discover neighboring routers • Auto configure 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

  5. Neighbor Discovery Message Format • ICMPv6 message structure and ICMPv6 types 133 -137 • All ND messages are sent with a hop limit of 255 Neighbor Discovery Message Neighbor Discovery Message Options Neighbor Discovery Message Header IPv6 Header Next Header(58)

  6. Neighbor Discovery Processes • Address Resolution • Resolve a neighbor's IPv6 address to its link-layer (MAC) address. • It is equivalent to ARP in IPv4. • Neighbor Unreachability Detection (NUD) • Determine that an address for use is not already in use by a neighbor node. • It is equivalent to Gratuitous ARP frames in IPv4. • Duplicate Address Detection (NAD) • Determine that the IPv6 layer of a neighbor is no longer receiving packets • Might not be the final destination but the reachability of the first hop of the destination

  7. Neighbor Discovery Processes • Router Discovery • A host discovers the local roter(s) on the attached link • Determine which local router is a default gateway • Switch to backup default router if the primary one is unavailable • Route Lifetime expiration • Neighbor Unreachability Detection (NUD) • Network Prefix(es) discovery • Parameters discovery (link MTU, Max Hop Limit, auto-config) • It is equivalent to ICMPv4 Router Discovery • Redirect Function • Process of a router inform a host of a better first hop IPv6 address to reach a destination • It is equivalent to ICMPv4 Redirect Message

  8. Address Resolution • An exchange of Neighbor Solicitation (NS) and Neighbor Advertisement (NA) messages to resolve the link-layer address of the next-hop address • Multicast Neighbor Solicitation message • Destination of NS is the solicited-node multicast address derived from target address • Source address of NS is the sender’s unicast address • Unicast Neighbor Advertisement message • Destination of NA is the requester’s unicast address • Source address and target address are same. • Both hosts update their neighbor caches • Unicast traffic can now be sent

  9. Host A Host B Address Resolution 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

  10. Multicast 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 Host A MAC: 00-10-5A-AA-20-A2 IP: FE80::210:5AFF:FEAA:20A2 Send multicast Neighbor Solicitation NS MAC: 00-60-97-02-6E-A5 IP: FE80::260:97FF:FE02:6EA5 Host B

  11. IPv6 Multicast Address FF…: Multicast Ethernet Addresses 33-33- Multicast NS Destination Derivation • The solicited-node multicast address is constructed from the prefix FF02::1:FF00:0/104 and the last 24 bits of a unicast IPv6 address • Mapping IPv6 Multicast Addresses to Ethernet Addresses

  12. Multicast NS Destination Address • Target Address: • IPv6 address (Unicast) • FE80::260:97FF:FE02:6EA5 • IP layer Destination Address: • Solicited-Node Address • FF02::1:FF02:6EA5 • Link layer Destination Address: • Multicast Ethernet Address • 33-33-FF-02-6E-A5

  13. Unicast 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 Host A MAC: 00-10-5A-AA-20-A2 IP: FE80::210:5AFF:FEAA:20A2 NA ‚ Send unicast Neighbor Advertisement MAC: 00-60-97-02-6E-A5 IP: FE80::260:97FF:FE02:6EA5 Host B

  14. Structure of NS Message Type Code Checksum Reserved Target Address Options = 135 = 0 . . .

  15. Type Code Checksum Router flag Solicited flag Override flag Reserved Target Address Options = 136 = 0 Structure of NA Message . . .

  16. Type Length Link-Layer Address Type Length Link-Layer Address Source and Target Link-Layer Address Options =1 • Target Link-Layer Address option . . . Source Link-Layer Address option =2 . . .

  17. Type Length Ethernet MAC Address = 1 Source and Target Link-Layer Address options for Ethernet For all ND options, Length field is the number of 8-byte blocks in the entire option.

  18. NS Sample Message Ethernet II, Src: 00:08:74:f8:6f:ee, Dst: 33:33:ff:dd:b8:37 Destination: 33:33:ff:dd:b8:37 Source: 00:08:74:f8:6f:ee Type: IPv6 (0x86dd) Internet Protocol Version 6 Version: 6 Traffic class: 0x00 Flowlabel: 0x00000 Payload length: 32 Next header: ICMPv6 (0x3a) Hop limit: 255 Source address: fe80::208:74ff:fef8:6fee Destination address: ff02::1:ffdd:b837

  19. Internet Control Message Protocol v6 • Type: 135 (Neighbor solicitation) • Code: 0 • Checksum: 0x158a (correct) • Target: fe80::20c:29ff:fedd:b837 • ICMPv6 options • Type: 1 (Source link-layer address) • Length: 8 bytes (1) • Link-layer address: 00:08:74:f8:6f:ee

  20. NA Sample Message • Ethernet II, Src: 00:08:74:f8:6f:ee, Dst: 00:0c:29:dd:b8:37 • Destination: 00:0c:29:dd:b8:37 • Source: 00:08:74:f8:6f:ee • Type: IPv6 (0x86dd) • Internet Protocol Version 6 • Version: 6 • Traffic class: 0x00 • Flowlabel: 0x00000 • Payload length: 32 • Next header: ICMPv6 (0x3a) • Hop limit: 255 • Source address: fe80::208:74ff:fef8:6fee • Destination address: fe80::20c:29ff:fedd:b837

  21. Internet Control Message Protocol v6 • Type: 136 (Neighbor advertisement) • Code: 0 • Checksum: 0x8633 (correct) • Flags: 0x60000000 • 0... .... .... .... .... .... .... .... = Not router • .1.. .... .... .... .... .... .... .... = Solicited • ..1. .... .... .... .... .... .... .... = Override • Target: fe80::208:74ff:fef8:6fee • ICMPv6 options • Type: 2 (Target link-layer address) • Length: 8 bytes (1) • Link-layer address: 00:08:74:f8:6f:ee

  22. 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 • There are five reachability States: • Incomplete, Stale, Delay, Probe, Reachable

  23. Host A Host B Reachablity confirmation 1.Neighbor Solicitation 2.Neighbor Advertisement 3.Neighbor Solicitation 4.Neighbor Advertisement

  24. Neighbor Unreachability States Send multicast NS NO ENTRY EXISTS INCOMPLETE Multicast NS retries exceeded Receive Solicited NA Reachable Time exceeded or unsolicited NA received REACHABLE Reachability confirmed by sending unicast NS and receiving solicited NA Reachability confirmed By upper layer protocol Delay time exceeded Send packet DELAY PROBE STALE Unicast NS retries exceeded

  25. 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 NA • The Destination Address is set to the link-local scope all-nodes multicast address (FF02::1)

  26. Duplicate Address Detection • Replace IPv4 ARP request and Gratutitos ARP • What is Gratuitous ARP? • IPv4 sets both source and target with the same IP address of the sender in ARP request • If it receives ARP reply, then the IP address is duplicate • Must be performed by all nodes (hosts & routers) • Performed before assigning a unicast address to an Interface • Performed on interface initialization • Not performed for anycast address • Link must be mulicast address

  27. Duplicate Address Detection • Accomplished by using NS (multicast) and NA messages • Node sends NS with: • Source address is unspecific address(::) • Destination address is tentative solicited-node address • Target address field is set to tentative IP address • The Source Link-layer Address option is not used • If address already exists, the particular node sends a NA reply with: • The destination address of NA is set to FF02::1 • The solicited flag is 0 because NS is not using the desired IP address

  28. Multicast NS for Duplicate Address Detection • 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 Host A Tentative IP: FEC0::2:260:8FF:FE52:F9D8 Send multicast Neighbor Solicitation NS Host B MAC: 00-60-08-52-F9-D8 IP: FEC0::2:260:8FF:FE52:F9D8

  29. Multicast NA for a Duplicate Address • 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 Host A Tentative IP: FEC0::2:260:8FF:FE52:F9D8 NA ‚ Send multicast Neighbor Advertisement Host B MAC: 00-60-08-52-F9-D8 IP: FEC0::2:260:8FF:FE52:F9D8

  30. Router Discovery • Attempts to discover the set of routers on the local link • Similar to IPv4 ICMP router discovery (RFC 1256) • In IPv6 RA messages, the Router Lifetime filed indicates the time that router can be considered a default router • Accomplished by sending a multicast Router Solicitation (FF02:2) and the receipt of a multicast Router Advertisement (FF02::1) message • If the router becomes unavailable, the condition is detected via neighbor unreachability instead of Router Lifetime in the RA messages • A new default router is chosen from default router list or the host sends a RS message to determine a new default router

  31. Multicast RS Message • 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 Host A MAC: 00-B0-D0-E9-41-43 IP: none Send multicast Router Solicitation RS MAC: 00-10-FF-D6-58-C0 IP: FE80::210:FFFF:FED6:58C0 Router

  32. Multicast RA Message • 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 Host A MAC: 00-B0-D0-E9-41-43 IP: none RA ‚ Send multicast Router Advertisement MAC: 00-10-FF-D6-58-C0 IP: FE80::210:FFFF:FED6:58C0 Router

  33. Type Code Checksum Reserved Options = 133 = 0 . . . Structure of the RS Message

  34. = 134 = 0 . . . Structure of the RA 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

  35. Type Length Prefix Length On-Link flag Autonomous flag Router Address flag Site prefix flag Reserved1 Valid Lifetime Preferred Lifetime Reserved2 Site Prefix Length Prefix = 3 = 4 Structure of the Prefix Information Option

  36. Type Length Reserved MTU = 5 = 1 Structure of the MTU Option

  37. Type Length Reserved Advertisement Interval = 7 = 1 Structure of the Advertisement Interval Option

  38. Type Length Reserved Home Agent Preference Home Agent Lifetime = 8 = 1 Structure of the Home Agent Information Option

  39. Structure of the Route Information Option Type Length Prefix Length Reserved 1 Preference Reserved 2 Route Lifetime Prefix = 9

  40. Sample RS message • Ethernet II, Src: 00:0c:29:7e:7e:86, Dst: 33:33:00:00:00:02 • Destination: 33:33:00:00:00:02 • Source: 00:0c:29:7e:7e:86 • Type: IPv6 (0x86dd) • Internet Protocol Version 6 • Version: 6 • Traffic class: 0x00 • Flowlabel: 0x00000 • Payload length: 16 • Next header: ICMPv6 (0x3a) • Hop limit: 255 • Source address: fe80::20c:29ff:fe7e:7e86 • Destination address: ff02::2

  41. Internet Control Message Protocol v6 • Type: 133 (Router solicitation) • Code: 0 • Checksum: 0x2b0d (correct) • ICMPv6 options • Type: 1 (Source link-layer address) • Length: 8 bytes (1) • Link-layer address: 00:0c:29:7e:7e:86

  42. Sample RA Message • Ethernet II, Src: 00:13:49:00:00:01, Dst: 33:33:00:00:00:01 • Destination: 33:33:00:00:00:01 • Source: 00:13:49:00:00:01 (ZyxelCom_00:00:01) • Type: IPv6 (0x86dd) • Internet Protocol Version 6 • Version: 6 • Traffic class: 0x00 • Flowlabel: 0x00000 • Payload length: 56 • Next header: ICMPv6 (0x3a) • Hop limit: 255 • Source address: fe80::213:49ff:fe00:1 • Destination address: ff02::1

  43. Internet Control Message Protocol v6 • Type: 134 (Router advertisement) • Code: 0 • Checksum: 0x96a0 (correct) • Cur hop limit: 64 • Flags: 0x00 • 0... .... = Not managed • .0.. .... = Not other • ..0. .... = Not Home Agent • ...0 0... = Router preference: Medium • Router lifetime: 1800 • Reachable time: 0 • Retrans time: 0

  44. ICMPv6 options • Type: 1 (Source link-layer address) • Length: 8 bytes (1) • Link-layer address: 00:13:49:00:00:01 • ICMPv6 options • Type: 3 (Prefix information) • Length: 32 bytes (4) • Prefix length: 64 • Flags: 0xc0 • 1... .... = Onlink • .1.. .... = Auto • ..0. .... = Not router address • ...0 .... = Not site prefix • Valid lifetime: 0x00278d00 • Preferred lifetime: 0x00093a80 • Prefix: fec0::

  45. Redirect • Sometimes hosts will pick the wrong next-hop • There are several routers • Send to a router although destination is connected to the same link • The router that receives the packet • will retransmit the correct hop • Send a Redirect message to the sender • After receive the Redirect message, the host will send the next message to the correct router

  46. Unicast Packet to the Router • Ethernet Header • Destination MAC is 00-AA-00-22-22-22 • IPv6 Header • Source Address is FEC0::1:2AA:FF:FE11:1111 • Destination Address is FEC0::2:2AA:FF:FE99:9999 Host A MAC: 00-AA-00-11-11-11 IP: FEC0::1:2AA:FF:FE11:1111 FE80::2AA:FF:FE11:1111 Send unicast packet Unicast Packet MAC: 00-AA-00-22-22-22 IP: FEC0::1:2AA:FF:FE22:2222 FE80::2AA:FF:FE22:2222 MAC: 00-AA-00-33-33-33 IP: FEC0::1:2AA:FF:FE33:3333 FE80::2AA:FF:FE33:3333 Router 3 Router 2

  47. Redirect ‚ Send unicast Redirect Redirect Message Sent by the Router • Ethernet Header • Destination MAC is 00-AA-00-11-11-11 • IPv6 Header • Source Address is FE80::2AA:FF:FE22:2222 • Destination Address is FEC0::1:2AA:FF:FE11:1111 • Hop limit is 255 • Redirect Header • Target Address is FE80::2AA:FF:FE33:3333 • Destination Address is FEC0::2:2AA:FF:FE99:9999 • Neighbor Discovery Options • Target Link-Layer Address is 00-AA-00-33-33-33 • Redirected Header Host A MAC: 00-AA-00-11-11-11 IP: FEC0::1:2AA:FF:FE11:1111 FE80::2AA:FF:FE11:1111 MAC: 00-AA-00-22-22-22 IP: FEC0::1:2AA:FF:FE22:2222 FE80::2AA:FF:FE22:2222 MAC: 00-AA-00-33-33-33 IP: FEC0::1:2AA:FF:FE33:3333 FE80::2AA:FF:FE33:3333 Router 2 Router 3

  48. Unicast Packet ƒForward unicast packet Unicast Packet Forwarded by the Router • Ethernet Header • Destination MAC is 00-AA-00-33-33-33 • IPv6 Header • Source Address is FEC0::1:2AA:FF:FE11:1111 • Destination Address is FEC0::2:2AA:FF:FE99:9999 Host A MAC: 00-AA-00-11-11-11 IP: FEC0::1:2AA:FF:FE11:1111 FE80::2AA:FF:FE11:1111 MAC: 00-AA-00-33-33-33 IP: FEC0::1:2AA:FF:FE33:3333 FE80::2AA:FF:FE33:3333 MAC: 00-AA-00-22-22-22 IP: FEC0::1:2AA:FF:FE22:2222 FE80::2AA:FF:FE22:2222 Router 2 Router 3

  49. Conceptual Host Data Structures • To facilitate interactions between neighboring nodes, RFC 2461 defines the following conceptual host data structures as an example of how to store information for ND processes: • Neighbor cache • The neighbor cache stores the on-link IP address of each neighbor, its corresponding link-layer address, and an indication of the neighbor's reachability state. • Destination cache • The destination cache stores information on next-hop IP addresses for destinations to which traffic has recently been sent. • Prefix list • The prefix list contains on-link prefixes. • Default router list • IP addresses corresponding to on-link routers that have sent Router Advertisement messages and are eligible to be default routers are included in the default router list.

  50. Destination Cache Neighbor Cache Destination Next-Hop Address PMTU Next-Hop Address Link Layer Address State Prefix List Default Router List Conceptual Host Data Structures

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