HP 6125G HP 6125G & 6125G/XG Blade Switches Layer 3 - IP Services Conf - Page 92

Neighbor reachability detection, Duplicate address detection

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Figure 45 Address resolution The address resolution operates in the following steps: 1. Host A multicasts an NS message. The source address of the NS message is the IPv6 address of the sending interface of Host A and the destination address is the solicited-node multicast address of Host B. The NS message contains the link-layer address of Host A. 2. After receiving the NS message, Host B determines whether the destination address of the packet is its solicited-node multicast address. If yes, Host B learns the link-layer address of Host A, and then unicasts an NA message containing its link-layer address. 3. Host A acquires the link-layer address of Host B from the NA message. Neighbor reachability detection After Host A acquires the link-layer address of its neighbor Host B, Host A can use NS and NA messages to check whether Host B is reachable. 1. Host A sends an NS message whose destination address is the IPv6 address of Host B. 2. If Host A receives an NA message from Host B, Host A decides that Host B is reachable. Otherwise, Host B is unreachable. Duplicate address detection After Host A acquires an IPv6 address, it performs Duplicate Address Detection (DAD) to check whether the address is being used by any other node (similar to the gratuitous ARP function in IPv4). DAD is accomplished through NS and NA message exchanges. Figure 46 shows the DAD process. Figure 46 Duplicate address detection 1. Host A sends an NS message whose source address is the unspecified address and whose destination address is the corresponding solicited-node multicast address of the IPv6 address to be detected. The NS message contains the IPv6 address. 2. If Host B uses this IPv6 address, Host B returns an NA message. The NA message contains the IPv6 address of Host B. 84

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84
Figure 45
Address resolution
The address resolution operates in the following steps:
1.
Host A multicasts an NS message. The source address of the NS message is the IPv6 address of the
sending interface of Host A and the destination address is the solicited-node multicast address of
Host B. The NS message contains the link-layer address of Host A.
2.
After receiving the NS message, Host B determines whether the destination address of the packet
is its solicited-node multicast address. If yes, Host B learns the link-layer address of Host A, and
then unicasts an NA message containing its link-layer address.
3.
Host A acquires the link-layer address of Host B from the NA message.
Neighbor reachability detection
After Host A acquires the link-layer address of its neighbor Host B, Host A can use NS and NA messages
to check whether Host B is reachable.
1.
Host A sends an NS message whose destination address is the IPv6 address of Host B.
2.
If Host A receives an NA message from Host B, Host A decides that Host B is reachable. Otherwise,
Host B is unreachable.
Duplicate address detection
After Host A acquires an IPv6 address, it performs Duplicate Address Detection (DAD) to check whether
the address is being used by any other node (similar to the gratuitous ARP function in IPv4). DAD is
accomplished through NS and NA message exchanges.
Figure 46
shows the DAD process.
Figure 46
Duplicate address detection
1.
Host A sends an NS message whose source address is the unspecified address and whose
destination address is the corresponding solicited-node multicast address of the IPv6 address to be
detected. The NS message contains the IPv6 address.
2.
If Host B uses this IPv6 address, Host B returns an NA message. The NA message contains the IPv6
address of Host B.