Guide to TCP/IP Fourth Edition Chapter 6: Neighbor Discovery in IPv6
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 2
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 3
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 4
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) 5
Comparing IPv6 Neighbor Discovery Protocols to IPv4 Protocols Table 6-1 Comparing IPv6 ND to IPv4 protocols 6
Neighbor Discovery Message Formats Five primary message types for ND Message formats Provide the foundation for IPv6 operational processes for node-to-node communications 7
Router Solicitation Determine if any IPv6 routers are on the network segment 8
Router Solicitation (cont d.) 9
Router Advertisement Inform hosts of link prefixes, link MTU, valid and preferred lifetimes Figure 6-3 ICMPv6 Router Advertisement packet structure 10
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Neighbor Solicitation Find (or verify) the link-layer address of a local node 13
Neighbor Solicitation (cont d.) 14
Neighbor Advertisement Sent as a response to a Neighbor Solicitation message 15
Neighbor Advertisement (cont d.) Table 6-5 ICMPv6 Neighbor Advertisement message format fields (continues) 16
Neighbor Advertisement (cont d.) 17
Redirect Inform a host of a better first-hop router for a destination 18
Redirect (cont d.) 19
Neighbor Discovery Option Formats 20
Source and Target Link-Layer Address Options Source Link-Layer Address option Used in Neighbor Solicitation, Router Solicitation, and Redirect messages 21
Source and Target Link-Layer Address Options (cont d.) 22
Source and Target Link-Layer Address Options (cont d.) Target Link-Layer Address option Used in Neighbor Advertisement and Router Advertisement messages 23
Source and Target Link-Layer Address Options (cont d.) 24
Prefix Information Option Used in Router Advertisement messages Contains prefix information for on-link addresses and prefixes used for address autoconfiguration 25
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Prefix Information Option (cont d.) 27
Redirected Header Option Sent in Redirect messages Contains all or part of the original IPv6 packet being redirected 28
Redirected Header Option (cont d.) 29
MTU Option Sent in Router Advertisement messages Provides a common MTU value for nodes on the same network segment 30
MTU Option (cont d.) 31
Advertisement Interval Option Used in Mobile IPv6 by mobile nodes receiving Router Advertisement messages For their movement detection algorithm 32
Advertisement Interval Option (cont d.) 33
Home Agent Information Option May include the Home Agent Information option in their Router Advertisement messages 34
Home Agent Information Option (cont d.) 35
Route Information Option Sent in Router Advertisement messages Specifies individual routes for hosts to add to their Default Router List 36
Route Information Option (cont d.) 37
Conceptual Host Model RFC 4861 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 38
Storing Neighbor Data on a Host Store following information for each active network interface Neighbor cache Destination cache Prefix list Default router list 39
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 40
Neighbor Discovery Process ND involves a number of processes: Address Resolution Neighbor Unreachability Detection Duplicate Address Detection Router Discovery Redirect Function 41
Address Resolution Figure 6-25 Address Resolution process: Step 1, Neighbor Solicitation 42
Address Resolution (cont d.) 43
Neighbor Unreachability Detection Used for node-to-neighbor-node verification of onlink 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 44
Duplicate Address Detection 45
Duplicate Address Detection (cont d.) 46
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 47
Router Discovery (cont d.) 48
Router Discovery (cont d.) 49
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 50
Redirect Messages (cont d.) 51
Redirect Messages (cont d.) 52
Redirect Messages (cont d.) 53
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 54
Summary (cont d.) Neighbor Solicitation and Neighbor Advertisement messages help nodes discover neighbor nodes that are on-link or off-link 55