Configuring parameters related to RA messages
You can enable an interface to send RA messages, and configure the interval for sending RA messages and parameters in RA messages. After receiving an RA message, a host can use these parameters to perform corresponding operations. Table 9 lists and describes the configurable parameters in an RA message.
The maximum interval for sending RA messages should be less than (or equal to) the router lifetime in RA messages, so the router can be updated through an RA message before expiration.
The values of the NS retransmission timer and the reachable time configured for an interface are sent to hosts via RA messages. Furthermore, this interface sends NS messages at the interval of the NS retransmission timer and considers a neighbor reachable within the reachable time.
Table 9: Parameters in an RA message and their descriptions
Parameters | Description |
|---|---|
Cur Hop Limit | When sending an IPv6 packet, a host uses the value to fill the Hop Limit field in IPv6 headers. The value is also filled into the Hop Limit field in the response packet of a device. |
Prefix Information options | After receiving the prefix information, the hosts on the same link can perform stateless autoconfiguration. |
MTU | Make sure that all nodes on a link use the same MTU value. |
M flag | Determines whether hosts use the stateful autoconfiguration to acquire IPv6 addresses. If the M flag is set to 1, hosts use the stateful autoconfiguration (for example, through a DHCP server) to acquire IPv6 addresses. Otherwise, hosts use the stateless autoconfiguration to acquire IPv6 addresses and generate IPv6 addresses according to their own link-layer addresses and the obtained prefix information. |
O flag | Determines whether hosts use stateful autoconfiguration to acquire other configuration information. If the O flag is set to 1, hosts use stateful autoconfiguration (for example, through a DHCP server) to acquire other configuration information. Otherwise, hosts use stateless autoconfiguration to acquire other configuration information. |
Router Lifetime | Tells the receiving hosts how long the advertising device can live. |
Retrans Timer | If the device fails to receive a response message within the specified time after sending an NS message, it will retransmit the NS message. |
Reachable Time | If the neighbor reachability detection shows that a neighbor is reachable, the device considers the neighbor reachable within the specified reachable time. If the device must send a packet to the neighbor after the specified reachable time expires, the device will reconfirm whether the neighbor is reachable. |
To allow sending of RA messages:
Step | Command | Remarks |
|---|---|---|
1. Enter system view. | system-view | N/A |
2. Enter interface view. | interface interface-type interface-number | N/A |
3. Disable RA message suppression. | undo ipv6 nd ra halt | By default, RA messages are suppressed. |
4. Configure the maximum and minimum intervals for sending RA messages. | ipv6 nd ra interval max-interval-value min-interval-value | Optional. By default, the maximum interval for sending RA messages is 600 seconds, and the minimum interval is 200 seconds. The device sends RA messages at random intervals between the maximum interval and the minimum interval. The minimum interval should be less than or equal to 0.75 times the maximum interval. |
To configure parameters related to RA messages:
Step | Command | Remarks |
|---|---|---|
1. Enter system view. | system-view | N/A |
2. Configure the hop limit. | ipv6 nd hop-limit value | Optional. 64 by default. |
3. Enter interface view. | interface interface-type interface-number | N/A |
4. Configure the prefix information in RA messages. | ipv6 nd ra prefix { ipv6-prefix prefix-length | ipv6-prefix/prefix-length } valid-lifetime preferred-lifetime [ no-autoconfig | off-link ] * | Optional. By default, no prefix information is configured for RA messages, and the IPv6 address of the interface sending RA messages is used as the prefix information with valid lifetime 2592000 seconds (30 days) and preferred lifetime 604800 seconds (seven days). |
5. Turn off the MTU option in RA messages. | ipv6 nd ra no-advlinkmtu | Optional. By default, RA messages contain the MTU option. |
6. Set the M flag bit to 1. | ipv6 nd autoconfig managed-address-flag | Optional. By default, the M flag bit is set to 0 and hosts acquire IPv6 addresses through stateless autoconfiguration. |
7. Set the O flag bit to 1. | ipv6 nd autoconfig other-flag | Optional. By default, the O flag bit is set to 0 and hosts acquire other configuration information through stateless autoconfiguration. |
8. Configure the router lifetime in RA messages. | ipv6 nd ra router-lifetime value | Optional. 1800 seconds by default. |
9. Set the NS retransmission timer. | ipv6 nd ns retrans-timer value | Optional. By default, the local interface sends NS messages at 1000 millisecond intervals, and the value of the Retrans Timer field in RA messages sent by the local interface is 0. The interval for retransmitting an NS message is determined by the receiving device. |
10. Set the reachable time. | ipv6 nd nud reachable-time value | Optional. By default, the neighbor reachable time on the local interface is 30000 milliseconds, and the value of the Reachable Time field in the RA messages sent by the local interface is 0. The neighbor reachable time is determined by the receiving device. |