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.)
|
Advertisement Value |
Default |
Page |
|---|---|---|
|
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 |
|
prefix |
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 |
|
length |
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) |
— |
|
maximum |
600 seconds |
Commands to configure the range for intervals between RA transmissions on a VLAN |
|
minimum |
200 seconds |
Commands to configure the range for intervals between RA transmissions on a VLAN |
|
current hop limit |
64 |
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.
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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.
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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.