ipv6 nd other-config-flag
Sets the O flag in RA messages to direct clients to use stateless DHCPv6 for DNS/domain info.
Definition: ipv6 nd other-config-flag is a Cisco IOS interface config command. Sets the Other (O) flag in IPv6 Router Advertisement (RA) messages. When O=1, clients that use SLAAC for their address are also instructed to contact a DHCPv6 server for additional configuration parameters such as DNS servers and domain names.
ipv6 nd other-config-flagWhen 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 STATELESSR1(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|statefulHosts 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.
ipv6 nd other-config-flag vs ipv6 nd managed-config-flag
Both commands set flags in IPv6 Router Advertisements to influence host configuration behavior, but they target different aspects: one for address assignment (M flag) and one for additional parameters (O flag). They are often confused because both involve DHCPv6, but their roles in stateful versus stateless configuration are distinct.
| Aspect | ipv6 nd other-config-flag | ipv6 nd managed-config-flag |
|---|---|---|
| Flag Set | Sets the Other (O) flag | Sets the Managed (M) flag |
| Effect on Client | Client uses SLAAC for address, then contacts DHCPv6 for other config | Client obtains address from DHCPv6 (stateful) |
| SLAAC Usage | SLAAC is still used for address | SLAAC is not used for address |
| Configuration Mode | Interface configuration | Interface configuration |
| Persistence | Persists in running-config | Persists in running-config |
| Typical Use Case | Stateless DHCPv6 (DHCPv6-light) | Stateful DHCPv6 |
Use ipv6 nd other-config-flag when you want hosts to use SLAAC for addresses but still obtain DNS and other settings from a DHCPv6 server.
Use ipv6 nd managed-config-flag when you want hosts to obtain both their IPv6 address and other configuration via stateful DHCPv6, disabling SLAAC for address assignment.
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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