Configure IPv6 Neighbor Discovery Protocol

IPv6 Neighbor Discovery protocol includes the following functions: address resolution, neighbor unreachable detection, duplicate address detection, router discovery / prefix discovery, address auto configuration and redirection.

The ICMPv6 packet type used by the ND protocol and its functions are shown in the following table.

Table 5-9 The ICMPv6 packet type used by the ND protocol and its functions

• Address resolution

Get the link-layer address of the neighbor node on one link, which is realized by the NS packet and NA packet.

• Neighbor unreachable detection

After getting the link-layer address of the neighbor node, verify whether the neighbor node is reachable via the NS packet and NA packet.

1. The node sends the NS packet, whose the destination address is the IPv6 address of the neighbor node
2. If receiving the confirm packet of the neighbor node, it is regarded that the neighbor is reachable. Otherwise, it is regarded that the neighbor is not reachable.

• Duplicate address detection

After the node gets one IPv6 address, it is necessary to use the duplicate address detection function to confirm whether the address is used by other nodes.

• Router discovery/prefix discovery and address auto configuration

Router discovery/prefix discovery indicates the node gets the neighbor router and its network prefix from the received RA packet, as well as other configuration parameters.

Address stateless auto configuration indicates that the node automatically configures the IPv6 address according to the information obtained by router discovery / prefix discovery.

Router discovery/prefix discovery is achieved through RS packets and RA packets.

• Re-direction

When the host starts, there may be only one default route to the default gateway in its routing table. When meeting certain conditions, the default gateway sends ICMPv6 redirect packets to the source host, informing the host to choose a better next hop for sending the subsequent packets.

Configuration Condition

None

Configure IPv6 Static Neighbor

Resolving the IPv6 address of the neighbor node into the link layer address can be realized by the address resolution function of the IPv6 ND protocol, or by configuring the static neighbor manually.

The IPv6 neighbor is uniquely identified by the IPv6 address of the neighbor node and the L3 interface connected to the neighbor node.

Table 5-10 Configure the IPv6 static neighbor

Configure the Age Time of the IPv6 Neighbor Entry in the STALE State

IPv6 neighbor entries have five reachability states: INCOMPLETE, REACHABLE, STALE, DELAY and PROBE. The STALE state indicates not knowing whether the neighbor is reachable or not. The neighbor entry in STALE state has an aging time, and the neighbor entries in STALE state reaching the aging time will migrate to the DELAY state.

Table 5-11 Configure the age time of the IPv6 neighbor entry in the STALE state

Configure the Re-transmission Interval of the NS Packet

When the device sends an NS packet, and if it does not receive a response within a specified time interval, it will resend the NS packet. The interval for re-sending NS packet can be configured by the following command.

Table 5-12 Configure the interval of re-sending the NS packet

Configure the Times of the IPv6 Duplicate Address Detection Sending the NS Packet

After the interface is configured with the IPv6 address, the NS packet is sent for duplicate address detection. If no response is received within a certain period of time, the NS packet is continued to be sent. When the number of NS packets sent reaches the set value, no response is received, the address is considered available.

Table 5-13 Configure the times of the IPv6 duplicate address detection sending the NS packet

Configure the Related Parameters of the RA Packet

Users can configure whether the interface sends the RA packet and the interval of sending the RA packet according to the actual situation, and can configure the parameters of the RA packet to inform the host. When the host receives the RA message, it can use these parameters to do the corresponding operation.

Table 5-14 The parameters and descriptions in the RA packet

Table 5-15 Configure the related parameters of the RA packet

Enable the Interface to Send the Re-direct Packet

After receiving the IPv6 packet that needs to be forwarded, the device finds that the receiving interface of the packet is the same as the sending interface by selecting the route. At this time, the device forwards the packet and sends back the redirect packet to the source, informing the source to re-select the correct next hop for sending the subsequent packets. By default, a device can send a redirect packet, but in some specific cases, the user can prevent the device from sending a redirect packet.

Table 5-16 Enable the function of the interface sending the re-direct packet