IPv6Interface Config

ipv6 nd other-config-flag

Sets the O flag in RA messages to direct clients to use stateless DHCPv6 for DNS/domain info.

Syntax·Interface Config

ipv6 nd other-config-flag

When to Use This Command

Stateless DHCPv6: clients get addresses via SLAAC but DNS/domain from DHCPv6.
Providing DNS information in IPv6 networks without full stateful DHCPv6.
Simpler alternative to stateful DHCPv6 when address tracking isn't required.
Used alone (without M flag) for stateless DHCPv6 scenarios.

Command Examples

Stateless DHCPv6 — SLAAC for address, DHCPv6 for DNS

R1(config)# interface GigabitEthernet0/1
R1(config-if)# ipv6 nd other-config-flag
R1(config)# ipv6 dhcp pool STATELESS
R1(config-dhcpv6)# dns-server 2001:4860:4860::8888
R1(config-dhcpv6)# domain-name example.com
R1(config)# interface GigabitEthernet0/1
R1(config-if)# ipv6 dhcp server STATELESS

R1(config-if)#

Clients auto-configure their IPv6 address via SLAAC (using the /64 prefix in the RA). The O=1 flag tells them to also contact DHCPv6 for DNS server and domain name. No 'address prefix' is needed in the pool since addresses are from SLAAC.

Verify O flag is set

R1# show ipv6 interface GigabitEthernet0/1 | include DHCP|stateless|stateful

  Hosts use stateless autoconfig for addresses.
  Hosts use DHCP to obtain other configuration.

'Stateless autoconfig' = SLAAC for addresses (M=0). 'DHCP to obtain other configuration' = O flag is set.

Understanding the Output

Verify with 'show ipv6 interface [intf]'. Look for 'Hosts use DHCP to obtain other configuration' (O=1 set). If only O is set (not M), clients use SLAAC for addresses — the DHCPv6 pool on the router only needs DNS/domain info, not an address prefix.

CCNA Exam Tips

CCNA exam tip: Stateless DHCPv6 = O flag only (no M flag). Stateful DHCPv6 = M flag (usually with O flag too).

CCNA exam tip: SLAAC alone (both M=0, O=0) provides no DNS — clients have no way to get DNS server info from the router in pure SLAAC.

CCNA exam tip: The O flag is sometimes called the 'other stateful' flag or just 'Other Config' flag on the exam.

CCNA exam tip: Both M and O flags can be set simultaneously — this is stateful DHCPv6 with additional config parameters.

Common Mistakes

Mistake 1: Forgetting to create a DHCPv6 pool with DNS when O flag is set — clients contact DHCPv6 but get no DNS response.

Mistake 2: Confusing 'stateless DHCPv6 (O flag)' with 'SLAAC (no flags)' — stateless DHCPv6 still requires a DHCPv6 server for DNS.

Mistake 3: Setting both M and O flags but not configuring an address prefix in the pool — clients request addresses but DHCPv6 has none to give.

Related Commands

ipv6 dhcp pool [name]

Creates a DHCPv6 server pool and enters DHCPv6 pool configuration mode. Used to configure stateful DHCPv6, where the server assigns IPv6 addresses and provides DNS/domain information to clients.

ipv6 dhcp server [pool-name]

Enables a DHCPv6 server on an interface and links it to a named DHCPv6 pool. Clients on that interface receive IPv6 addresses and parameters from the specified pool.

ipv6 nd managed-config-flag

Sets the Managed (M) flag in IPv6 Router Advertisement (RA) messages sent from this interface. When M=1, clients are instructed to obtain their IPv6 address from a DHCPv6 server (stateful DHCPv6) rather than using SLAAC.

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