dhcrelay6

dhcrelay6 is a DHCP relay agent for IPv6, distributed as part of the ISC DHCP software family. Its primary purpose is to forward DHCPv6 messages between clients on local IPv6 networks and one or more DHCPv6 servers that may reside on different networks or behind routers. By doing so, it allows centralized DHCPv6 services to serve clients across multiple subnets without requiring a server on every segment.

In the DHCPv6 relay model, clients send requests to a local relay, which encapsulates and forwards them to a designated DHCPv6 server using Relay-Forward messages. The server replies with Relay-Reply messages, which the relay forwards back to the originating client. The relay does not itself allocate addresses; it simply transports messages and may insert or modify relay-specific options as configured.

dhcrelay6 can be configured to listen on one or more IPv6 interfaces and to forward requests to one or more DHCPv6 servers. Configuration is typically provided through command-line options and, on some systems, an optional configuration file. Some deployments use a dedicated dhcrelay6 binary, while others rely on a single relay binary with IPv6-specific behavior.

Deployment considerations include ensuring proper network reachability between clients and servers, appropriate firewall rules, and the ability to scale for multiple subnets. It is commonly used in networks where DHCPv6 servers are centralized or separated by routers, enabling consistent address assignment and options across subnets.

See also: DHCPv6, relay concepts in DHCP, ISC DHCP suite, and related relay tools.