HP IPv6 5400zl, IPv6 6200yl, IPv6 2900, IPv6 3500yl Duplicate Address Detection DAD, DAD Operation

IPv6 Addressing Configuration

Duplicate Address Detection (DAD)

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Neighbor and router solicitations must originate on the same VLAN as the receiving device. To support this operation, IPv6 is designed to discard any incoming neighbor or router solicitation that does not have a value of 255 in the IP Hop Limit field. For a complete list of requirements, refer to RFC 246.

When a pair of IPv6 devices in a VLAN exchange communication, they enter each other's IPv6 and corresponding MAC addresses in their respective neighbor caches. These entries are maintained for a period of time after communication ceases, and then dropped.

To view or clear the content of the neighbor cache, refer to “Viewing and Clearing the IPv6 Neighbors Cache” on page 5-2.

For related information, refer to:

■RFC 2461: “Neighbor Discovery for IP Version 6 (IPv6)”

Duplicate Address Detection (DAD)

Duplicate Address Detection verifies that a configured unicast IPv6 address is unique before it is assigned to a VLAN interface on the switch. DAD is enabled in the default IPv6 configuration, and can be reconfigured, disabled, or re-enabled at the global config command level. DAD can be useful in helping to troubleshoot erroneous replies to DAD requests, or where the neighbor cache contains a large number of invalid entries due to an unauthorized station sending false replies to the switch's neighbor discovery queries. If DAD verifies that a unicast IPv6 address is a duplicate, the address is not used. If the link-local address of the VLAN interface is found to be a duplicate of an address for another device on the interface, then the interface stops processing IPv6 traffic.

DAD Operation

On a given VLAN interface, when a new unicast address is configured, the switch runs DAD for this address by sending a neighbor solicitation to the All- Nodes multicast address (ff02::1). This operation discovers other devices on the VLAN and verifies whether the proposed unicast address assignment is unique on the VLAN. (During this time, the address being checked for unique- ness is held in a tentative state, and cannot be used to receive traffic other than neighbor solicitations and neighbor advertisements.) A device that receives the neighbor solicitation responds with a Neighbor Advertisement

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