Configuring route advertisement

Configure route advertisement in IPv6 for neighbor discovery (ND).

About this task

IPv6 nodes on the same link use ND to discover link-layer addresses and to obtain and advertise various network parameters and reachability information. ND combines the services provided by Address Resolution Protocol (ARP) and router discovery for IPv4.

Procedure

  1. Enter Interface Configuration mode:

    enable

    configure terminal

    interface GigabitEthernet {slot/port[/sub-port][-slot/port[/sub-port]][,...]} or interface vlan <1–4059>

    Note

    Note

    If the platform supports channelization and the port is channelized, you must also specify the sub-port in the format slot/port/sub-port.

  2. Configure the number of neighbor solicitation messages from duplicate address detection:

    ipv6 nd dad-ns <0–600>

  3. Configure the hop limit sent in router advertisements:

    ipv6 nd hop-limit <0–255>

  4. Enable managed address configuration (M-bit) on the router:

    ipv6 nd managed-config-flag

  5. Configure the MTU for router advertisements:

    ipv6 nd mtu <0–9500>

  6. Enable other stateful configuration (O-bit) on the router:

    ipv6 nd other-config-flag

  7. Configure the router lifetime included in router advertisement:

    ipv6 nd ra-lifetime <0–9000>

  8. Configure the neighbor reachable time:

    ipv6 nd reachable-time <0–3600000>

  9. Configure the time between neighbor solicitation messages:

    ipv6 nd retransmit-timer <0-4294967295>

  10. Configure the maximum time allowed between sending unsolicited multicast router advertisements:

    ipv6 nd rtr-advert-max-interval <4–1800>

  11. Configure the minimum time allowed between sending unsolicited multicast router advertisements:

    ipv6 nd rtr-advert-min-interval <3–1350>

  12. Enable periodic router advertisement messages:

    ipv6 nd send-ra

Example

Configure the maximum time between sending unsolicited router advertisements:

Switch:1(config-if)#ipv6 nd rtr-advert-max-interval 700

Configure the minimum time between sending unsolicited router advertisements:

Switch:1(config-if)#ipv6 nd rtr-advert-min-interval 500

Enable periodic router advertisement messages:

Switch:1(config-if)#ipv6 nd send-ra

Variable Definitions

Use the data in the following table to use the ipv6 nd commands.

Variable

Value

dad-ns <0–600>

Specifies the number of neighbor solicitation messages for duplicate address detection (DAD).

A value of 0 disables the DAD process on this interface.

A value of 1 sends one advertisement without retransmissions.

hop-limit <0–255>

Specifies the current hop limit field sent in router advertisements from this interface.

The value must be the current diameter of the Internet.

A value of zero indicates that the advertisement does not specify a hop-limit value.

The default is 64.

managed-config-flag

Enables the system to configure the M-bit, or managed address configuration flag, in the router advertisements

When set, the M-bit flag indicates that addresses are available through DHCPv6.

If the M flag is set, the O flag is redundant because DHCPv6 returns all available configuration information.

If neither the M nor O flags are set, no information is available through DHCPv6.

The default is disabled.

mtu <0–9500>

Shows the MTU value sent in router advertisements on this interface.

A value of zero indicates that the system sends no MTU options.

The default is 0.

other-config-flag

Enables the O-bit, or other stateful configuration, flag in the router advertisement.

Other stateful configuration autoconfigures received information without addresses.

When set, the O-bit flag indicates that other configuration information is available through DHCPv6; for example, DNS-related information or information about other servers within the network.

If neither the M nor O flags are set, no information is available through DHCPv6.

The default is disabled.

ra-lifetime <0–9000>

Specifies a value placed in the router lifetime field of router advertisements sent from this interface.

This value must be either 0, or 4 to 9000 seconds.

A value of zero indicates that the system is not a default router.

The default is 1800.

reachable-time <0–3600000>

Specifies a value (in milliseconds) placed in the router advertisement message sent by the router.

The value zero means unspecified (by this system).

Configure the amount of time that a remote IPv6 node is considered reachable after a reachability confirmation event.

The default is 0.

retransmit-timer <0-4294967295>

Specifies a value (in milliseconds) placed in the retransmit timer field in the router advertisement message sent from this interface.

The value zero means unspecified (by this system).

The value configures the amount of time the system waits for the transmission to occur.

The default is 0.

rtr-advert-max-interval <4–1800>

Specifies the maximum interval (in seconds) at which the transmission of route advertisements occurs on this interface.

The default is 600.

rtr-advert-min-interval <3–1350>

Specifies the minimum interval (in seconds) at which the transmission of route advertisements occurs on this interface.

The default is 200.

send-ra

Specifies whether the router sends periodic router advertisements and responds to router solicitations on this interface.

The default is enabled.

Use the data in the following table to use the interface command.

Variable

Value

<1-4059>

Specifies the VLAN ID in the range of 1 to 4059. By default, VLAN IDs 1 to 4059 are configurable and the system reserves VLAN IDs 4060 to 4094 for internal use. On switches that support the vrf-scaling and spbm-config-mode boot configuration flags, if you enable these flags, the system also reserves VLAN IDs 3500 to 3998. VLAN ID 1 is the default VLAN and you cannot create or delete VLAN ID 1.

{slot/port[/sub-port][-slot/port[/sub-port]][,...]}

Identifies the slot and port in one of the following formats: a single slot and port (slot/port), a range of slots and ports (slot/port-slot/port), or a series of slots and ports (slot/port,slot/port,slot/port). If the platform supports channelization and the port is channelized, you must also specify the sub-port in the format slot/port/sub-port.

System Interface Values Versus Advertised Values

There are differences in the relationship between the system interface values and advertised values related to Neighbor Disovery (ND). The information in this section describes differences and similarities and provides examples for important IPv6 interface and IPv6 ND commands.

Comparison of Default Values per Interface and as Advertised

The following table compares the default behavior of values per interface and advertised values.

Default values per interface

Default advertised values

hop-limit 64

hop-limit 64

mtu 1500

mtu 0 (unspecified)

reachable-time 30000 ms

reachable-time 0 (unspecified)

retransmit-timer 1000 ms

retransmit-timer 0 (unspecified)

What Happens When You Change the per Interface Value and the Advertised Value?

When you change per-interface values from default to non-default values, the system changes the advertised values to match the interface values.

For example, when you enter the ipv6 interface mtu 1300 command the values become

  • interface mtu 1300

  • advertised mtu 1300

Then, when you enter the show ipv6 nd interface command, the system marks the mtu value with an (i) which signifies that the ND advertised value is inherited from the interface configuration.

Example: Changing both values

Switch:1(config-if)#ipv6 interface mtu 1300

Switch:1(config-if)#
show ipv6 nd interface GigabitEthernet 1/1
================================================================================
                             Port Ipv6 Nd
================================================================================
IFID BTR RTR- MAX- MIN-    LIFE- MANAG  OTHER DAD-NS MTU    HOP  REACH- RETRANS-
         ADV  INT  INT     TIME         LIMIT TIME   TIME        ABLE   MIT
                   FLAG    CONF
--------------------------------------------------------------------------------
320  1/1 True 600  200      0    False False   1    1300(i) 64(d) 0(d)  0(d)
Note: (s) = Set, (d) = Default, (i) = inherit
--------------------------------------------------------------------------------

What Happens When You Change the per Interface Value but do not Change the Advertised Value?

To change the per-interface value from the default value to a non-default value but retain the advertised value of 0 (unspecified), you must enter two commands.

For example, to set the reachable-time to 60000 but retain the advertised value of the reachable-time parameter at 0, enter the following commands:

ipv6 interface reachable-time 6000

ipv6 nd reachable-time 0

When you enter the show ipv6 nd interface command, the system marks the reachable-time value with an (s) to signify that this value is explicitly set by the ND configuration.

Example: Changing only the per interface value

Switch:1(config-if)#ipv6 interface reachable-time 60000

Switch:1(config-if)#ipv6 nd reachable-time 0

Switch:1(config-if)#
show ipv6 nd interface GigabitEthernet 1/1
================================================================================
                             Port Ipv6 Nd
================================================================================
IFID BTR RTR- MAX- MIN- LIFETIME MANAG OTHER DAD-NS  MTU    HOP  REACH- RETRANS-
         ADV  INT  INT  CONF           LIMIT  TIME   TIME        ABLE   MIT
                        FLAG
--------------------------------------------------------------------------------
320  1/1 True 600  200  0        False False    1   1500(i) 64(d) 0(s)  0(d)
Note: (s) = Set, (d) = Default, (i) = inherit
---------------------------------------------------------------------------------
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