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

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