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

Guide to TCP/IP Fourth Edition

Chapter 6:Neighbor Discovery in IPv6

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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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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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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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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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Comparing IPv6 Neighbor Discovery Protocols to IPv4 Protocols

Table 6-1 Comparing IPv6 ND to IPv4 protocols


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Neighbor Discovery Message Formats

• Five primary message types for ND

• Message formats – Provide the foundation for IPv6 operational

processes for node-to-node communications


Router Solicitation

• Determine if any IPv6 routers are on the network segment

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Router Solicitation (cont’d.)


Router Advertisement

• Inform hosts of link prefixes, link MTU, valid and preferred lifetimes

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Figure 6-3 ICMPv6 Router Advertisement packet structure




Neighbor Solicitation

• Find (or verify) the link-layer address of a local node


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Neighbor Solicitation (cont’d.)


Neighbor Advertisement

• Sent as a response to a Neighbor Solicitation message


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Neighbor Advertisement (cont’d.)

Table 6-5 ICMPv6 Neighbor Advertisement message format fields (continues)


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Neighbor Advertisement (cont’d.)


Redirect

• Inform a host of a better first-hop router for a destination


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Redirect (cont’d.)


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Neighbor Discovery Option Formats


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Source and Target Link-Layer Address Options

• Source Link-Layer Address option– Used in Neighbor Solicitation, Router Solicitation,

and Redirect messages


Source and Target Link-Layer Address Options (cont’d.)


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• Target Link-Layer Address option– Used in Neighbor Advertisement and Router

Advertisement messages




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Prefix Information Option

• Used in Router Advertisement messages

• Contains prefix information for on-link addresses and prefixes used for address autoconfiguration



Prefix Information Option (cont’d.)


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Redirected Header Option

• Sent in Redirect messages – Contains all or part of the original IPv6 packet being

redirected


Redirected Header Option (cont’d.)


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MTU Option

• Sent in Router Advertisement messages– Provides a common MTU value for nodes on the

same network segment


MTU Option (cont’d.)


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Advertisement Interval Option

• Used in Mobile IPv6 by mobile nodes receiving Router Advertisement messages– For their movement detection algorithm


Advertisement Interval Option (cont’d.)


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Home Agent Information Option

• May include the Home Agent Information option in their Router Advertisement messages


Home Agent Information Option (cont’d.)


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Route Information Option

• Sent in Router Advertisement messages– Specifies individual routes for hosts to add to their

Default Router List


Route Information Option (cont’d.)


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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


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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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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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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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Address Resolution

Figure 6-25 Address Resolution process: Step 1, Neighbor Solicitation


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Address Resolution (cont’d.)


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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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Duplicate Address Detection


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Duplicate Address Detection (cont’d.)


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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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Router Discovery (cont’d.)


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Router Discovery (cont’d.)


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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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Redirect Messages (cont’d.)


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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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Summary (cont’d.)

• Neighbor Solicitation and Neighbor Advertisement messages help nodes discover neighbor nodes that are on-link or off-link


Documents

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