1. Guide to TCP/IP Fourth Edition
Chapter 6:
Neighbor Discovery in IPv6

2. Objectives
Describe Neighbor Discovery in IPv6 and how it compares to ARP in IPv4
Explain Neighbor Discovery message interaction between hosts and routers
Describe the process flow for how a node determines that its IPv6 address is unique and how it communicates on the IPv6 network
Explain each of the main Neighbor Discovery messages and what information each of them provides to a node
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3. Objectives (cont’d.)
Identify the data components that a host stores in local memory to facilitate IPv6 communications with other nodes
Describe how a host receives updates concerning better first-hops to access nodes not on-link
Identify, when capturing and reviewing ICMPv6 data using a network protocol analyzer, the Neighbor Discovery messages and option fields in those packets using specific decode filters
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4. Understanding Neighbor Discovery
IPv6 Neighbor Discovery (ND) protocol
Specified in RFC 4861 and RFC 5942
Permits nodes to:
Find out what link they are located on
Learn link address prefixes
Learn where a link’s working routers reside
Discover link neighbors
Discover which neighbors are active
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5. Understanding Neighbor Discovery (cont’d.)
ND uses five ICMPv6 message types:
Router Solicitation (RS) (ICMPv6 type 133)
Router Advertisement (RA) (ICMPv6 type 134)
Neighbor Solicitation (NS) (ICMPv6 type 135)
Neighbor Advertisement (NA) (ICMPv6 type 136)
Redirect (ICMPv6 type 137)
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6. Comparing IPv6 Neighbor Discovery Protocols to IPv4 Protocols
Table 6-1 Comparing IPv6 ND to IPv4 protocols
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7. Neighbor Discovery Message Formats
Five primary message types for ND
Message formats
Provide the foundation for IPv6 operational processes for node-to-node communications
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8. Router Solicitation
Determine if any IPv6 routers are on the network segment
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9. Router Solicitation (cont’d.)
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10. Router Advertisement
Inform hosts of link prefixes, link MTU, valid and preferred lifetimes
Figure 6-3 ICMPv6 Router Advertisement packet structure
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13. Neighbor Solicitation
Find (or verify) the link-layer address of a local node
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14. Neighbor Solicitation (cont’d.)
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15. Neighbor Advertisement
Sent as a response to a Neighbor Solicitation message
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16. Neighbor Advertisement (cont’d.)
Table 6-5 ICMPv6 Neighbor Advertisement message format fields (continues)
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17. Neighbor Advertisement (cont’d.)
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18. Redirect Inform a host of a better first-hop router for a destination
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19. Redirect (cont’d.)
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20. Neighbor Discovery Option Formats
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21. Source and Target Link-Layer Address Options
Source Link-Layer Address option
Used in Neighbor Solicitation, Router Solicitation, and Redirect messages
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22. Source and Target Link-Layer Address Options (cont’d.)
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23. Source and Target Link-Layer Address Options (cont’d.)
Used in Neighbor Advertisement and Router Advertisement messages
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24. Source and Target Link-Layer Address Options (cont’d.)
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25. Prefix Information Option
Used in Router Advertisement messages
Contains prefix information for on-link addresses and prefixes used for address autoconfiguration
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27. Prefix Information Option (cont’d.)
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28. Redirected Header Option
Sent in Redirect messages
Contains all or part of the original IPv6 packet being redirected
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29. Redirected Header Option (cont’d.)
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30. MTU Option Sent in Router Advertisement messages
Provides a common MTU value for nodes on the same network segment
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31. MTU Option (cont’d.)
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32. Advertisement Interval Option
Used in Mobile IPv6 by mobile nodes receiving Router Advertisement messages
For their movement detection algorithm
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33. Advertisement Interval Option (cont’d.)
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34. Home Agent Information Option
May include the Home Agent Information option in their Router Advertisement messages
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35. Home Agent Information Option (cont’d.)
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36. Route Information Option
Sent in Router Advertisement messages
Specifies individual routes for hosts to add to their Default Router List
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37. Route Information Option (cont’d.)
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38. Conceptual Host Model RFC 4861 Conceptual host model
Defines what must occur for the ND process to be successful
Conceptual host model
Represents information that a host should maintain to communicate effectively in an IPv6 network
Primarily concerned with operational behavior by hosts
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39. Storing Neighbor Data on a Host
Store following information for each active network interface
Neighbor cache
Destination cache
Prefix list
Default router list
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40. Conceptual Sending Algorithm
Node needs to find out the IP address of next-hop
By examining its destination cache to learn the associated link-layer address
By examining its neighbor cache
If the node does not have these addresses available
It invokes a process called “next-hop determination”
To populate its caches and lists with its neighbor’s addressing information
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41. Neighbor Discovery Process
ND involves a number of processes:
Address Resolution
Neighbor Unreachability Detection
Duplicate Address Detection
Router Discovery
Redirect Function
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42. Address Resolution
Figure 6-25 Address Resolution process: Step 1, Neighbor Solicitation
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43. Address Resolution (cont’d.)
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44. Neighbor Unreachability Detection
Used for node-to-neighbor-node verification of on-link communications capability
Nodes consider neighbors reachable
If there have been recent communications by an upper-layer protocol
Five states for a neighbor cache entry
INCOMPLETE
REACHABLE
STALE
DELAY
PROBE
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45. Duplicate Address Detection
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46. Duplicate Address Detection (cont’d.)
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47. Router Discovery Used by nodes to:
Discover neighbor routers on the local link
Learn prefixes
Configure their default gateway, and other possible parameters relating to autoconfiguration
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48. Router Discovery (cont’d.)
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49. Router Discovery (cont’d.)
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50. Redirect Messages Routers send Redirect messages
To inform hosts that there is a better first-hop router to send packets to a specific destination
Used by routers to inform a host that a destination node is an on-link neighbor
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51. Redirect Messages (cont’d.)
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52. Redirect Messages (cont’d.)
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53. Redirect Messages (cont’d.)
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54. Summary IPv6 introduces a Neighbor Discovery protocol
Helps support stateless autoconfiguration and provides improved support for mobile users
The conceptual host model represents information that a host should maintain to communicate effectively in an IPv6 network
Router Solicitation and Router Advertisement messages help nodes learn network prefixes and other stateless and/or stateful address autoconfiguration capabilities
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55. Summary (cont’d.)
Neighbor Solicitation and Neighbor Advertisement messages help nodes discover neighbor nodes that are on-link or off-link
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