ASDM Book 1: Cisco ASA Series General Operations ASDM Configuration Guide, 7.2

Neighbor Solicitation Messages

Neighbor solicitation messages (ICMPv6 Type 135) are sent on the local link by nodes attempting to discover the link-layer addresses of other nodes on the local link. The neighbor solicitation message is sent to the solicited-node multicast address. The source address in the neighbor solicitation message is the IPv6 address of the node sending the neighbor solicitation message. The neighbor solicitation message also includes the link-layer address of the source node.

After receiving a neighbor solicitation message, the destination node replies by sending a neighbor advertisement message (ICPMv6 Type 136) on the local link. The source address in the neighbor advertisement message is the IPv6 address of the node sending the neighbor advertisement message; the destination address is the IPv6 address of the node that sent the neighbor solicitation message. The data portion of the neighbor advertisement message includes the link-layer address of the node sending the neighbor advertisement message.

After the source node receives the neighbor advertisement, the source node and destination node can communicate. Figure 32-1 shows the neighbor solicitation and response process.

Figure 32-1 IPv6 Neighbor Discovery—Neighbor Solicitation Message

Neighbor solicitation messages are also used to verify the reachability of a neighbor after the link-layer address of a neighbor is identified. When a node wants to verifying the reachability of a neighbor, the destination address in a neighbor solicitation message is the unicast address of the neighbor.

Neighbor advertisement messages are also sent when there is a change in the link-layer address of a node on a local link. When there is such a change, the destination address for the neighbor advertisement is the all-nodes multicast address.

Neighbor Reachable Time

The neighbor reachable time enables detecting unavailable neighbors. Shorter configured times enable detecting unavailable neighbors more quickly, however, shorter times consume more IPv6 network bandwidth and processing resources in all IPv6 network devices. Very short configured times are not recommended in normal IPv6 operation.

Duplicate Address Detection

During the stateless autoconfiguration process, Duplicate Address Detection verifies the uniqueness of new unicast IPv6 addresses before the addresses are assigned to interfaces (the new addresses remain in a tentative state while Duplicate Address Detection is performed). Duplicate Address Detection is performed first on the new link-local address. When the link-local address is verified as unique, then Duplicate Address Detection is performed all the other IPv6 unicast addresses on the interface.

Duplicate Address Detection is suspended on interfaces that are administratively down. While an interface is administratively down, the unicast IPv6 addresses assigned to the interface are set to a pending state. An interface returning to an administratively up state restarts Duplicate Address Detection for all of the unicast IPv6 addresses on the interface.

When a duplicate address is identified, the state of the address is set to DUPLICATE, the address is not used, and the following error message is generated:

If the duplicate address is the link-local address of the interface, the processing of IPv6 packets is disabled on the interface. If the duplicate address is a global address, the address is not used. However, all configuration commands associated with the duplicate address remain as configured while the state of the address is set to DUPLICATE.

If the link-local address for an interface changes, Duplicate Address Detection is performed on the new link-local address and all of the other IPv6 address associated with the interface are regenerated (Duplicate Address Detection is performed only on the new link-local address).

The ASA uses neighbor solicitation messages to perform Duplicate Address Detection. By default, the number of times an interface performs Duplicate Address Detection is 1.

Router Advertisement Messages

An ASA can participate in router advertisements so that neighboring devices can dynamically learn a default router address. Router advertisement messages (ICMPv6 Type 134) are periodically sent out each IPv6 configured interface of the ASA. The router advertisement messages are sent to the all-nodes multicast address. Figure 32-2 shows an example of how to send router advertisement messages on an IPv6 configured interface.

Figure 32-2 IPv6 Neighbor Discovery—Router Advertisement Message

Router advertisement messages typically include the following information:

• One or more IPv6 prefix that nodes on the local link can use to automatically configure their IPv6 addresses.
• Lifetime information for each prefix included in the advertisement.
• Sets of flags that indicate the type of autoconfiguration (stateless or stateful) that can be completed.
• Default router information (whether the router sending the advertisement should be used as a default router and, if so, the amount of time (in seconds) the router should be used as a default router).
• Additional information for hosts, such as the hop limit and MTU a host should use in packets that it originates.
• The amount of time between neighbor solicitation message retransmissions on a given link.
• The amount of time a node considers a neighbor reachable.

Router advertisements are also sent in response to router solicitation messages (ICMPv6 Type 133). Router solicitation messages are sent by hosts at system startup so that the host can immediately autoconfigure without needing to wait for the next scheduled router advertisement message. Because router solicitation messages are usually sent by hosts at system startup, and the host does not have a configured unicast address, the source address in router solicitation messages is usually the unspecified IPv6 address (0:0:0:0:0:0:0:0). If the host has a configured unicast address, the unicast address of the interface sending the router solicitation message is used as the source address in the message. The destination address in router solicitation messages is the all-routers multicast address with a scope of the link. When a router advertisement is sent in response to a router solicitation, the destination address in the router advertisement message is the unicast address of the source of the router solicitation message.

You can configure the following settings for router advertisement messages:

• The time interval between periodic router advertisement messages.
• The router lifetime value, which indicates the amount of time IPv6 nodes should consider the ASA to be the default router.
• The IPv6 network prefixes in use on the link.
• Whether or not an interface transmits router advertisement messages.

Unless otherwise noted, the router advertisement message settings are specific to an interface and are entered in interface configuration mode.

Static IPv6 Neighbors

You can manually define a neighbor in the IPv6 neighbor cache. If an entry for the specified IPv6 address already exists in the neighbor discovery cache—learned through the IPv6 neighbor discovery process—the entry is automatically converted to a static entry. Static entries in the IPv6 neighbor discovery cache are not modified by the neighbor discovery process.

Configuring the Neighbor Solicitation Message Interval

To configure the interval between IPv6 neighbor solicitation retransmissions on an interface, perform the following steps.

Detailed Steps

Step 1 Choose Configuration > Device Setup > Interfaces.

Step 2 Choose the interface on which to configure the neighbor solicitation interval. The interface must have been configured with an IPv6 address. see Configuring IPv6 Addressing for more information.

Step 3 Click Edit. The Edit Interface dialog box appears with three tabs: General, Advanced, and IPv6.

Step 4 Click the IPv6 tab.

Step 5 In the NS Interval field, enter the time interval.

Step 6 Click OK.

Step 7 Click Apply to save the running configuration.

Configuring the Neighbor Reachable Time

To configure the amount of time that a remote IPv6 node is considered reachable after a reachability confirmation event has occurred, perform the following steps.

Detailed Steps

Step 1 Choose Configuration > Device Setup > Interfaces.

Step 2 Choose the interface for which you want to configure the time. The interface must have been configured with an IPv6 address. For more information, see Configuring IPv6 Addressing.

Step 3 Click Edit. The Edit Interface dialog box appears with three tabs: General, Advanced, and IPv6.

Step 4 Click the IPv6 tab.

Step 5 In the Reachable Time field, enter a valid value.

Step 6 Click OK.

Step 7 Click Apply to save the running configuration.

Detailed Steps

Step 1 Choose Configuration > Device Setup > Interfaces.

Step 2 Select the interface for which you want to configure the time.

The interface must have been configured with an IPv6 address. For more information, see Configuring IPv6 Addressing.

Step 3 Click Edit. The Edit Interface dialog box appears with three tabs: General, Advanced, and IPv6.

Step 4 Click the IPv6 tab.

Step 5 In the RA Interval field, enter a valid transmission interval value.

Note (Optional) To add a router advertisement transmission interval value in milliseconds instead, check the RA Interval in Milliseconds check box, and enter a value from 500 to 1800000.

Step 6 Click OK.

Step 7 Click Apply to save the running configuration.

Configuring the Router Lifetime Value

To configure the router lifetime value in IPv6 router advertisements on an interface, perform the following steps.

Detailed Steps

Step 1 Choose Configuration > Device Setup > Interfaces.

Step 2 Select the interface you want to configure.

The interface must have been configured with an IPv6 address. For more information see Configuring IPv6 Addressing.

Step 3 Click Edit.

The Edit Interface dialog box appears with three tabs: General, Advanced, and IPv6.

Step 4 Click the IPv6 tab.

Step 5 In the RA Lifetime field, enter a valid lifetime value.

Step 6 Click OK.

Step 7 Click Apply to save the running configuration.

Configuring DAD Settings

To specify DAD settings on the interface, perform the following steps.

Detailed Steps

Step 1 Choose Configuration > Device Setup > Interfaces.

Step 2 Select the interface you want to configure.

The interface must have been configured with an IPv6 address. For more information, see Configuring IPv6 Addressing.

Step 3 Click Edit.

The Edit Interface dialog box appears with three tabs: General, Advanced, and IPv6.

Step 4 Click the IPv6 tab.

Step 5 Enter the number of allowed DAD attempts. This setting configures the number of consecutive neighbor solicitation messages that are sent on an interface while DAD is performed on IPv6 addresses. Valid values range from 0 to 600. A zero value disables DAD processing on the specified interface. The default is one message.

Suppressing Router Advertisement Messages

Router advertisement messages are automatically sent in response to router solicitation messages. You may want to disable these messages on any interface for which you do not want the ASA to supply the IPv6 prefix (for example, the outside interface).

To suppress the router lifetime value in IPv6 router advertisements on an interface, perform the following steps.

Detailed Steps

Step 1 Choose Configuration > Device Setup > Interfaces.

Step 2 Select the interface for which you want to suppress the router advertisement transmissions. The interface must have been configured with an IPv6 address.

Step 3 Click Edit.

The Edit Interface dialog box appears with three tabs: General, Advanced, and IPv6.

Step 4 Click the IPv6 tab.

Step 5 Check the Suppress RA check box.

Configuring Address Config Flags for IPv6 DHCP Relay

You can add a flag to IPv6 router advertisements to inform IPv6 autoconfiguration clients to use DHCPv6 to obtain an IPv6 address and/or additional information such as the DNS server address.

Detailed Steps

Step 1 Choose Configuration > Device Setup > Interfaces.

Step 2 Select the interface that you want to configure.

Step 3 Click Edit.

The Edit Interface dialog box appears with three tabs: General, Advanced, and IPv6.

Step 4 Click the IPv6 tab.

Step 5 Check the Hosts should use DHCP for address config check box to set the Managed Address Config flag in the IPv6 router advertisement packet. This flag informs IPv6 autoconfiguration clients that they should use DHCPv6 to obtain addresses, in addition to the derived stateless autoconfiguration address.

Check the Hosts should use DHCP for non-address config check box to set the Other Address Config flag in the IPv6 router advertisement packet. This flag informs IPv6 autoconfiguration clients that they should use DHCPv6 to obtain additional information from DHCPv6, such as the DNS server address.

Configuring the IPv6 Prefix in Router Advertisements

To configure the which IPv6 prefixes are included in IPv6 router advertisements, perform the following steps.

Detailed Steps

Step 1 Choose Configuration > Device Setup > Interfaces.

Step 2 Select the interface for which you want to suppress the router advertisement transmissions. The interface must have been configured with an IPv6 address.

Step 3 Click Edit.

The Edit Interface dialog box appears with three tabs: General, Advanced, and IPv6.

Step 4 Click the IPv6 tab.

Step 5 In the Interface IPv6 Prefixes area, click Add.

The Add IPv6 Prefix for Interface dialog box appears.

Step 6 Enter the IPv6 address with the prefix length.

Step 7 (Optional) To configure the IPv6 address manually, check the No Auto-Configuration check box. This setting indicates to hosts on the local link that the specified prefix cannot be used for IPv6 autoconfiguration.

Step 8 (Optional) To indicate that the IPv6 prefix is not advertised, check the No Advertisements check box.

Step 9 (Optional) The Off Link check box indicates that the specified prefix is assigned to the link. Nodes sending traffic to addresses that contain the specified prefix consider the destination to be locally reachable on the link. This prefix should not be used for on-link determination.

Step 10 In the Prefix Lifetime area, click the Lifetime Duration radio button, and specify the following:

a. A valid lifetime for the prefix in seconds from the drop-down list. This setting is the amount of time that the specified IPv6 prefix is advertised as being valid. The maximum value represents infinity. Valid values are from 0 to 4294967295. The default is 2592000 (30 days).

b. A preferred lifetime for the prefix from the drop-down list. This setting is the amount of time that the specified IPv6 prefix is advertised as being preferred. The maximum value represents infinity. Valid values are from 0 to 4294967295. The default setting is 604800 (seven days).

Step 11 To define a prefix lifetime expiration date, click the Lifetime Expiration Date radio button, and specify the following:

a. Choose a valid month and day from the drop-down list, and then enter a time in hh:mm format.

b. Choose a preferred month and day from the drop-down list, and then enter a time in hh:mm format.

Step 12 Click OK to save your settings.

The Interface IPv6 Prefixes Address field appears with the preferred and valid dates.

Configuring a Static IPv6 Neighbor

Make sure that IPv6 is enabled on at least one interface before trying to add a neighbor, or ASDM returns an error message indicating that the configuration failed.

For information about configuring IPv6 addresses, see Configuring IPv6 Addressing.

To add an IPv6 static neighbor, perform the following steps.

Detailed Steps

Step 1 Choose Configuration > Device Management > Advanced > IPv6 Neighbor Discovery Cache.

Step 2 Click Add.

The Add IPv6 Static Neighbor dialog box appears.

Step 3 From the Interface Name drop-down list, choose an interface on which to add the neighbor.

Step 4 In the IP Address field, enter the IPv6 address that corresponds to the local data-link address, or click the ellipsis (...) to browse for an address.

If an entry for the specified IPv6 address already exists in the neighbor discovery cache—learned through the IPv6 neighbor discovery process—the entry is automatically converted to a static entry.

Step 5 In the MAC address field, enter the local data-line (hardware) MAC address.

Step 6 Click OK.

Note Before you apply the changes and save the configuration, you can click Reset to cancel any changes and restore the original values.

Step 7 Click Apply to save the running configuration.

Related Documents for IPv6 Prefixes

RFCs for IPv6 Prefixes and Documentation