Router advertisement general operation

An IPv6 routing switch configured as a member of a given VLAN transmits RAs for use by hosts on the VLAN or tunnel. It also transmits unscheduled RAs in response to router solicitations received from IPv6 hosts on the VLAN. The values a host receives in an RA are applied to settings that have not already been configured on the host by the system operator. (Values in an RA can also replace host settings that were learned from a previous RA.)

When IPv6 unicast routing is enabled, RAs are transmitted by default on VLANs or tunnels enabled for IPv6 and configured with an IPv6 link-local address, unless RA transmission has been explicitly suppressed. RA configuration includes:

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managed flag (M-bit)

Not set

VLAN or tunnel context ND configuration

other-config-flag (O-bit)

Not set

VLAN or tunnel context ND configuration


The prefix of any global unicast IPv6 address configured on the VLAN interface1

Commands to configure global unicast prefix and lifetime for hosts on a VLAN


N/A; based on existing configuration

valid lifetime

2,592,000 seconds (30 days)

preferred lifetime

604,800 seconds (7 days)

autoconfig (A-bit)

Set (host autoconfig enabled)

on-link (L-bit)

Set (use prefix on subject VLAN)


600 seconds

Commands to configure the range for intervals between RA transmissions on a VLAN


200 seconds

Commands to configure the range for intervals between RA transmissions on a VLAN

current hop limit


ipv6 nd ra hop-limit

default lifetime

1800 seconds (3 x max. transmission interval)

ipv6 nd ra lifetime

reachable time

Unspecified (0)

ipv6 nd ra reachable-time

retransmission timer

Unspecified (0)

ipv6 nd ra ns-interval

Default operation excludes prefixes of stateless autoconfigured addresses.

  • Enabling IPv6 unicast routing on a routing switch initiates transmission of RAs on active, IPv6-enabled VLANs unless RA transmission has been suppressed.

  • RAs are not routed.

  • A host response to an RA depends on how the host implements IPv6. Generally, settings in an RA received by a host replaces settings received from an earlier RA. Settings configured directly on a host by an operator may override values received in an RA for the same settings.

  • When a host receives a default "unspecified" value in an RA, the host applies either its own current setting for that value, or the defaults specified in RFC 4861 or other applicable RFCs, depending on how IPv6 is implemented in the host.

  • The M-bit and O-bit flags enable RAs to be configured either to act as the sole source of host addressing and related settings, or to direct the host to use a DHCPv6 server for some or all such settings.