Neighbor Discovery

Neighbor Discovery

 

    IPv6 Neighbor Discovery (ND) �橐恍� messages 的集合 , 其功用主要是用��Q定在同一�� link 上相�的 node.

ND 取代了在 IPv4 中的 ARP, ICMP, Router Discovery, 和 ICMP Redirect, �K且提供了一些�~外的功能 .

 

  Neighbor Discovery Message Format

 

      ND �息�裼� ICMPv6 �息�Y�� , 和 ICMPv6 type 133 到 137. ND �息包含一�� ND �息�祟^ , 包含一�� ICMPv6

�祟^和 ND �息�Y料 , 以及零��或多�� ND options. 如下�D .

 

       

the  format of a Neighbor Discovery message

 

    此外 ND messages 包含五��不同的功能

 

Ø            Router Solicitation

Ø            Router Advertisement

Ø            Neighbor Solicitation

Ø            Neighbor Advertisement

Ø            Redirect

 

   ND messages options 提供一些�~外的�Y� , 包含 MAC address,  在此 link 上的 prefix and MTU �Y� , 以及 redirection data.

    此外所有的 ND messages are sent with a hop limit of 255.  ��一�� ND message 被接受到�r , 在 IPv6 封包�谖恢械� hop limit

    �谖��先被�z查 , 若此值不是 255 �r�t�G�� . ( 但�楹卧O�� 255, �K不是很清楚),   以下便��Υ宋宸N messages 分�e做�f明

 

 

   Neighbor Solicitation

 

        此�息是被用�戆l�F在相同 link 上的 IPv6 node 的 link-layer address. 它包含了�l送者的 link-layer address. Typical

   Neighbor Solicitation are multicast for address resolution and unicast when the reachability of a neighboring node is being

Verified

 

�e例�f明 , ��此 link �� ethernet , in the Ethernet header of the Neighbor Solicitation message

 

Ø            在�碓次恢�谖�榘l送者的�W路卡的 MAC address

Ø            ��於 multicast Neighbor Solicitation 而言 ,  目的位址�谖�� Etherner  MAC address that corresponds to the solicited

-node Multicast address of the target.   ��於 unicast  Neighbor Solicitation 而言 ,  目地位址�橄懔� node 的 MAC address

 

   In the IPv6 header of the Neighbor Solicitation message

 

Ø            �碓次恢�榘l送者的 IPv6 address

Ø            ��於 multicast Neighbor Solicitation 而言 ,  目的位址�谖�� solicited-node Multicast address of the target.  ��於 unicast

 Neighbor Solicitation 而言 ,  目地位址�谖�� unicast  or anycast address of target

Ø            Hop limit field is set to 255

 

 

           the format of the Neighbor Solicitation message

 

       Checksum --  此�谖�� ICMPv6 的 checksum

       Reserved --  此�谖�� 32bit, 保留�o未�硎褂们以O�� 0

       Target Address �C 128bit, 指 IP address of the target

       Source Link-Layer Address option �C  包含�l送者的 link-layer address

 

 

 

   Neighbor Advertisement

 

       此�N�息�� IPv6 node ��接收到 Neighbor Solicitation message �r所做的回�� .  一�� IPv6 node 也���l送 unsolicited Neighbor

Advertisements 告知�近的 node 其 link-layer address 已改�

 

�e例�f明 , 假�O local link �� ethernet , in the Ethernet header of the Neighbor Advertisement message

 

Ø            �碓次恢�谖�榘l送�@�W路介面的 MAC address

Ø            �� solicited Neighbor Advertisement 而言其目地位址�橐婚_始�l送 Neighbor Solicitation message 的 node 的 unicast

 MAC address  �� an unsolicited Neighbor Advertisement 而言其目地位址��  33-33-00-00-00-01, the Ethernet MAC address

corresponding  to the link-Local scope all-nodes multicast address

 

In the IPv6 header of the Neighbor Advertisement message

 

Ø            �碓次恢�榘l送者介面的 link-local address

Ø            �� solicited Neighbor Advertisement 而言其目地位址�橐婚_始�l送 Neighbor Solicitation message 的 node 的 unicast  IP

address  �� an unsolicited Neighbor Advertisement 而言其目地位址�� link-local scope all-nodes multicast address (FF02::1)

Ø            Hop limit field is set to 255

 

 

   Address Resolution

 

            The address resolution process for IPv6 nodes consists of an exchange of Neighbor Solicitation and Neighbor Advertisement

messages   to resolve the link-layer address of the on-link next-hop address for a given destination. The sending host sends a

multicast  Neighbor Solicitation message on the appropriate interface. The multicast address of the Neighbor Solicitation message

is  the solicited-node multicast   address derived from the target IP address. The Neighbor Solicitation message includes the link-layer

address  of the sending host in the Source    Link-Layer Address option. For information on how a host determines the next-hop

address  for a destination, see “Host Sending Algorithm.

 

When the target host receives the Neighbor Solicitation message, it updates its own neighbor cache based on the source address

of  the   Neighbor Solicitation message and the link-layer address in the Source Link-Layer Address option. Next, the target node sends

a  unicast   Neighbor Advertisement to the Neighbor Solicitation sender. The Neighbor Advertisement includes the Target Link-Layer

Address   option.   After receiving the Neighbor Advertisement from the target, the sending host updates its neighbor cache with an entry

for  the target   based upon the information in the Target Link-Layer Address option. At this point, unicast IPv6 traffic between the sending

host  and the target of the Neighbor   Solicitation can be sent.

 

  Address Resolution Example :

Host A has an Ethernet MAC address of 00-AA- 00-11-11 -11 and a corresponding link-local address of FE80::2AA:FF:FE11:1111.

 Host B has an Ethernet MAC address of 00-AA-00-22-22-22 and a corresponding link-local address of FE80::2AA:FF:FE22:2222. To

send  a packet to Host B, Host A must use address resolution to resolve Host B’s link-layer address.Based on Host B’s IP address,

Host A sends a solicited   -node multicast Neighbor Solicitation to the address of FF02::1:FF22:2222 .

 

 

Host B, having registered the solicited-node multicast address of 33-33-FF-22-22-22 with its Ethernet adapter, receives and processes

the  Neighbor   Solicitation. Host B responds with a unicast Neighbor Advertisement message .