This chapter focuses on the IPv6 application of management features that support both IPv6 and IPv4 operation. For additional information on these features, see the current management and configuration guide for your switch.
Neighbor discovery occurs when there is communication between the switch and another, reachable IPv6 device on the same VLAN. A neighbor destination is reachable from a given source address if a confirmation (neighbor solicitation) has been received at the source verifying that traffic has been received at the destination.
The switch maintains an IPv6 neighbor cache that is populated as a result of communication with other devices on the same VLAN.
You can view the contents of the neighbor cache using the commands described in this section.
For more information, see Viewing and clearing the IPv6 Neighbor Cache.
Neighbor discovery occurs when there is communication between IPv6 devices on a VLAN. The Neighbor Cache retains data for a given neighbor until the entry times out. For more on this topic, see Neighbor Discovery (ND).
Syntax:
Displays IPv6 neighbor information currently held in the neighbor cache. After a period without communication with a given neighbor, the switch drops that neighbor's data from the cache. The command lists neighbors for all VLAN interfaces on the switch or for only the specified VLAN. The following fields are included for each entry in the cache:
IPv6 Address : Lists the 128-bit addresses for the local host and any neighbors (on the same VLAN) with whom there has been recent communication.
MAC Address : The MAC Address corresponding to each of the listed IPv6 addresses.
VLAN
<vid>: Optional. Causes the switch to list only the IPv6 neighbors on a specific VLAN configured on the switch.Type : Appears only when VLAN is not specified and indicates whether the corresponding address is local (configured on the switch) or dynamic (configured on a neighbor device).
Age : Appears only when the VLAN is specified and indicates the length of time the entry has remained unused.
Port : Identifies the switch port on which the entry was learned. If this field is empty for a given address, the address is configured on the switch itself.
State : A neighbor destination is reachable from a given source address if confirmation has been received at the source verifying that traffic has been received at the destination. This field shows the reachability status of each listed address:
INCMP : (Incomplete): Neighbor address resolution is in progress, but has not yet been determined.
REACH : (Reachable): The neighbor is known to have been reachable recently.
STALE : A timeout has occurred for reachability of the neighbor, and an unsolicited discovery packet has been received from the neighbor address. If the path to the neighbor is then used successfully, this state is restored to REACH.
DELAY : Indicates waiting for a response to traffic sent recently to the neighbor address. The time for determining the neighbor's reachability has been extended.
PROBE : The neighbor may not be reachable. Periodic, unicast neighbor solicitations are being sent to verify reachability.
Neighbor Cache without specifying a VLAN
HP Switch(config)# show ipv6 neighbor IPv6 ND Cache Entries IPv6 Address MAC Address State Type Port ––––––––––––––––––––––––––– ––––––––––––– ––––– ––––––– –––– 2001:db8:260:212::101 0013c4–dd14b0 STALE dynamic 1 2001:db8:260:214::1:15 001279–88a100 REACH local fe80::1:1 001279–88a100 REACH local fe80::10:27 001560–7aadc0 REACH dynamic 3 fe80::213:c4ff:fedd:14b0 0013c4–dd14b0 REACH dynamic 1
Neighbor Cache content for a specific VLAN
HP Switch(config)# show ipv6 neighbor vlan 10 IPv6 ND Cache Entries IPv6 Address MAC Address State Age Port –––––––––––––––––––––––– ––––––––––––– ––––– ––––––––––––– –––– 2001:db8:260:212::101 0013c4–dd14b0 STALE 5h:13m:44s 1 2001:db8:260:214::1:15 001279–88a100 REACH 11h:15m:23s 17 fe80:1a3::1:1 001279–88a100 REACH 9h:35m:11s 12 fe80:::10:27 001560–7aadc0 REACH 22h:26m:12s 3 fe80::213:c4ff:fedd:14b0 0013c4–dd14b0 REACH 23 0h:32m:36s 1
When there is an event such as a topology change or an address change, the neighbor cache may have too many entries to allow efficient use. Also, if an unauthorized client is answering DAD or normal neighbor solicitations with invalid replies, the neighbor cache may contain a large number of invalid entries and communication with some valid hosts may fail and/or the show ipv6 neighbors command output may become too cluttered to efficiently read. In such cases, the fastest way to restore optimum traffic movement on a VLAN may be to statically clear the neighbor table instead of waiting for the unwanted entries to time-out.
Syntax:
Executed at the global config level, this command removes all non-local IPv6 neighbor addresses and corresponding MAC addresses from the neighbor cache, except neighbor entries specified as next-hops for active routes. Note that the Layer-2 address information for any next-hop route is cleared until the route is refreshed in the neighbor cache.
Clearing the IPv6 neighbors cache
HP Switch(config)# clear ipv6 neighbors HP Switch(config)# show ipv6 neighbors HP Switch# show ipv6 neighbors IPv6 ND Cache Entries IPv6 Address MAC Address State Type Port ––––––––––––––––––––––––––– ––––––––––––– ––––– ––––––– –––– fe80::213:c4ff:fedd:14b0 000000–000000 INCMP dynamic
For an active-route next-hop, the MAC address and source port data is removed, and the State is set to “Incomplete” (INCMP) until the route is refreshed in the neighbor cache.