Quiz Entry - updated: 2026.07.14
How do you configure a DHCPv6 (Dynamic Host Configuration Protocol version 6) relay agent on a Cisco router, and how does it differ from DHCPv4 (Dynamic Host Configuration Protocol version 4) relay?
Use ipv6 dhcp relay destination on the client-facing interface, specifying the DHCPv6 server address and optionally the egress interface.
Configuration:
R1(config)# interface gigabitethernet 0/0/1
R1(config-if)# ipv6 dhcp relay destination 2001:db8:acad:1::2 G0/0/0
Command breakdown:
2001:db8:acad:1::2— the DHCPv6 server's IPv6 addressG0/0/0— the egress interface to reach the server (only required when the next-hop address is a link-local address)
DHCPv4 vs. DHCPv6 relay comparison:
| Feature | DHCPv4 | DHCPv6 |
|---|---|---|
| Command | ip helper-address |
ipv6 dhcp relay destination |
| Configured on | Client-facing interface | Client-facing interface |
| Egress interface | Not specified | Optional (needed for LLA (Link-Local Address) next-hop) |
| Also forwards | 8 UDP (User Datagram Protocol) services (DNS (Domain Name System), TFTP (Trivial File Transfer Protocol), etc.) | DHCPv6 only |
Verification:
R1# show ipv6 dhcp interface
Look for: GigabitEthernet0/0/1 is in relay mode
Tip: Unlike ip helper-address which forwards 8 different UDP services, ipv6 dhcp relay destination is DHCPv6-specific — it only relays DHCP, not DNS or TFTP.
Go deeper:
RFC 8415 §19 — Relay Agent Behavior — the Relay-forward/Relay-reply messages ipv6 dhcp relay destinationimplements.