Neighbor Discovery

Neighbor Discovery Processes

  • Router discovery : Router Solicitation, Router Adverstisement
  • Prefix discovery  : Distinguish onlink vs off link
  • Parameter discovery : additional operational parms
  • Address auto configuration : DHCP
  • Address resolution : Neighbor Solicitation, Neighbor Advertisement
  • Next-hop determination
  • Neighbor unreachability detection
  • Duplicate address detection
  • Redirect function : Better next hop

Neighbor Discovery Messages

  • Router Solicitation (133)
  • Router Advertisement (134)
  • Neighbor Solicitation (135)
  • Neighbor Advertisement (136)
  • Redirect (137)
    > All are accomplished by ICMP messages

Summary of ND Message and Options

  • Router Solicitation
    • Source Link-Layer Address
  • Router Advertisement
    • Source Link-Layer Address
    • Prefix Information
    • MTU
    • Advertisement Interval
    • Home Agent Information
    • Router Information
  • Neighbor Solicitation
    • Source Link-Layer Address
  • Neighbor Advertisement
    • Target Link-Layer Address
  • Redirect
    • Redirected Header
    • Target Link-Layer Address

Neighbor Discovery Processes

  • Address resolution (including duplicate address detection)
  • Router discovery (including prefix and parameter discovery)
  • Neighbor unreachability detection
  • Redirect function

Address Resolution Process

  • An exchange of NS and NA 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

Address Resolution Message

Host A – MAC: 00-10-5A-AA-20-A2 / IP : FE80::210:5AFF:FEAA:20A2
Host B – MAC: 00-60-97-02-6E-A5 / IP: FE80::260:97FF:FE02:6EA5

  1. Multicast Neighbor Solicitation
    Ethernet Header
        Destination MAC is 33-33-FF-02-6E-A5 (Ethernet Multicast Address)
    IPv6 Header
        Source Address is FE80::210:5AFF:FEAA:20A2
        Destination Address is FF02::1:FF02:6EA5 (Solited-node Address)
        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
    
  2. 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 Solicitation Header
        Target Address is FE80::260:97FF:FE02:6EA5
    Neighbor Discovery Option
        Source Link-Layer Address is 00-60-97-02-6E-A5
    

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

Neighbor Unreachability States

Neighbor Unreachability States
from IPv6 Addressing (TechRef)

Duplicate Adddress Detection

Host A – Tentative IP: FEC0::2:260:8FF:FE52:F9D8
Host B – MAC: 00-60-08-52-F9-D8 / IP: FEC0::2:260:8FF:FE52:F9D8

  1. Multicast Neighbor Solicitation message
    Ethernet Header
        Dest MAC is 33-33-FF-52-F9-D8 (Ethernet Multicast Address)
    IPv6 Header
        Source Address is :: (Unspecified address)
        Destination Address is FF02::1:FF52:F9D8 (Solited-node Address)
        Hop limit is 255
    Neighbor Solicitation Header
        Target Address is FEC0::2:260:8FF:FE52:F9D8
    
  2. Multicast Neighbor Advertisement message
    Ethernet Header
        Destination MAC is 33-33-00-00-00-01 (Ethernet Multicast Address)
    IPv6 Header
        Source Address is FEC0::2:260:8FF:FE52:F9D8
        Destination Address is FF02::1 (All-nodes multicast address)
        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
    

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

Router Discovery Message

Host A – MAC: 00-B0-D0-E9-41-43 / IP: none
Router – MAC: 00-10-FF-D6-58-C0 / IP: FE80::210:FFFF:FED6:58C0

  1. Multicast Router Solicitation Message
    Ethernet Header
        Destination MAC is 33-33-00-00-00-02 (Ethernet Multicast Address)
    IPv6 Header
        Source Address is :: (Unspecified address)
        Destination Address is FF02::2 (All node Multicast Address)
        Hop limit is 255
    Router Solicitation Header
    
  2. Multicast Router Advertisement Message
    Ethernet Header
        Destination MAC is 33-33-00-00-00-01 (Ethernet Multicast Address)
    IPv6 Header
        Source Address is FE80::210:FFFF:FED6:58C0
        Destination Address is FF02::1 (All node Multicast Address)
        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 
    

Ref.
1. Neighbor Discovery
2. TCP/IP Fundamentals for microsoft windows
3. IPv6 Addressing
4. IPv6 Neighbor Discovery

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