In which configuration mode is ipv6 dhcp relay destination [ipv6-addr] used?

The ipv6 dhcp relay destination [ipv6-addr] command is entered in Interface Config mode on Cisco IOS devices.

IPv6Interface Config

ipv6 dhcp relay destination [ipv6-addr]

Forwards DHCPv6 client messages to a remote server across routed networks.

Definition: ipv6 dhcp relay destination [ipv6-addr] is a Cisco IOS interface config command. Configures an interface to relay DHCPv6 messages from clients to a remote DHCPv6 server. Used when the DHCPv6 server is not on the same segment as the clients.

Syntax·Interface Config

ipv6 dhcp relay destination <ipv6-address>

When to Use This Command

Relaying DHCPv6 from access-layer switches/routers to a central DHCPv6 server.
Large enterprise deployments where a single DHCPv6 server serves multiple VLANs.
Replacing multiple local DHCPv6 pools with one central managed server.
IPv6 equivalent of 'ip helper-address' for IPv4 DHCP relay.

Command Examples

Configure DHCPv6 relay to a central server

R1(config)# interface GigabitEthernet0/1
R1(config-if)# ipv6 dhcp relay destination 2001:db8:ffff::1

R1(config-if)#

GigabitEthernet0/1 is now a DHCPv6 relay agent. Client Solicit messages arriving on this interface are forwarded to the DHCPv6 server at 2001:db8:ffff::1. This is the IPv6 equivalent of 'ip helper-address'.

Verify relay configuration

R1# show ipv6 dhcp interface GigabitEthernet0/1

GigabitEthernet0/1 is in relay mode
  Relay destinations:
    2001:db8:ffff::1

The interface shows 'relay mode' with the destination server address — not 'server mode'. An interface can be relay OR server, not both.

Understanding the Output

Verify with 'show ipv6 dhcp interface' — it shows 'relay mode' and the relay destination. An interface cannot be both a server and a relay agent. The relay destination can be a global unicast or link-local address (with the 'interface' keyword added if link-local).

CCNA Exam Tips

CCNA exam tip: IPv4 uses 'ip helper-address'; IPv6 uses 'ipv6 dhcp relay destination' — same concept, different command.

CCNA exam tip: A router interface can be a DHCPv6 relay OR server, not both simultaneously.

CCNA exam tip: DHCPv6 relay must be configured on the interface facing the CLIENTS, not the server.

CCNA exam tip: The relay destination address must be reachable from the relay router.

Common Mistakes

Mistake 1: Configuring relay on the server-facing interface — it should be on the CLIENT-facing interface.

Mistake 2: Setting the relay destination to an unreachable address — DHCPv6 Solicit packets are forwarded but no Reply arrives.

Mistake 3: Confusing relay destination (DHCPv6 server's address) with the server's pool address.

ipv6 dhcp relay destination [ipv6-addr] vs ipv6 dhcp server [pool-name]

Both commands are configured under interface configuration mode for DHCPv6 operations, but they serve opposite roles: one relays requests to a remote server, the other provides server functionality locally. They are commonly confused because both are applied to interfaces and involve DHCPv6 configuration.

Aspect	ipv6 dhcp relay destination [ipv6-addr]	ipv6 dhcp server [pool-name]
Role	Relays DHCPv6 messages to a remote server	Acts as DHCPv6 server for clients on the interface
Configuration	Specifies destination IPv6 address of DHCPv6 server	Associates interface with a local DHCPv6 pool
Dependency	Requires a DHCPv6 server reachable at the destination address	Requires a configured DHCPv6 pool on the device
Traffic Flow	Client messages are forwarded to the server; server responses relayed back	Client messages are processed locally; device assigns addresses from pool
Typical Use	When DHCPv6 server is on a different network segment	When the device itself is the DHCPv6 server for its directly connected clients

Use ipv6 dhcp relay destination [ipv6-addr] when the DHCPv6 server resides on a different network segment and you need to forward client messages to it.

Use ipv6 dhcp server [pool-name] when the router or switch should act as the DHCPv6 server for clients on that interface, using a predefined address pool.

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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