Ccna routing and Switching Complete Study Guide

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Neighbor Discovery (NDP)

ICMPv6 also takes over the task of finding the address of other devices on the local link. 

The Address Resolution Protocol is used to perform this function for IPv4, but that’s been 

renamed Neighbor Discovery (ND or NDP) in ICMPv6. This process is now achieved via 

a multicast address called the solicited node address because all hosts join this multicast 

group upon connecting to the network.

Neighbor discovery enables these functions:

 

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Determining the MAC address of neighbors

 

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Router solicitation (RS) FF02::2

 

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Router advertisements (RA) FF02::1

 

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Neighbor solicitation (NS)

 

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Neighbor advertisement (NA)

 

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Duplicate address detection (DAD)

The part of the IPv6 address designated by the 24 bits farthest to the right is added 

to the end of the multicast address FF02:0:0:0:0:1:FF/104. When this address is queried, 

the corresponding host will send back its layer 2 address. Devices can find and keep track 

of other neighbor devices on the network in pretty much the same way. When I talked 

about RA and RS messages earlier in the CCENT chapters, and told you that they use 

multicast traffic to request and send address information, that too is actually a function of 

ICMPv6—specifically, neighbor discovery.

In IPv4, the protocol IGMP was used to allow a host device to tell its local router that it was 

joining a multicast group and would like to receive the traffic for that group. This IGMP function 

has been replaced by ICMPv6, and the process has been renamed multicast listener discovery.

With IPv4, our hosts could have only one default gateway configured, and if that router 

went down we had to fix the router, change the default gateway, or run some type of vir-

tual default gateway with other protocols created as a solution for this inadequacy in IPv4. 

Figure 20.5 shows how IPv6 devices find their default gateways using neighbor discovery.

f I g u r e   2 0 . 5     Router solicitation (RS) and router advertisement (RA)

FF02::1 Use me! (RA)

Internet