DHCPv6 prefix delegation

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Overview

This sample demonstrates IPv6 prefix delegation as specified in RFC 8415. It can be built in two roles:

  • Requesting router (default): a DHCPv6 client requests an IPv6 address (IA_NA) and a delegated prefix (IA_PD) on its upstream (WAN) interface. Each downstream (LAN) interface is then assigned a distinct /64 carved from the delegated prefix and advertised via Router Advertisements, so that hosts on the downstream links can auto-configure addresses (SLAAC).

  • Delegating router / server (overlay-server.conf): a DHCPv6 server hands out addresses from 2001:db8:abcd::/64 and delegates prefixes out of 2001:db8:beef::/48, one /56 per client. The two pools are deliberately disjoint: if a client was delegated the very subnet its own WAN address comes from, it would re-advertise that subnet on its LAN and two links would end up with the same prefix.

Network interfaces

Prefix delegation needs at least two links, so the requesting-router build brings up two network interfaces. On native_sim board these are two TAP interfaces:

  • zeth0 – upstream (WAN), runs the DHCPv6 client (interface index 1),

  • zeth1 – downstream (LAN), where the delegated prefix is advertised (interface index 2).

The number of downstream links is bounded by CONFIG_NET_DHCPV6_MAX_DOWNSTREAM; raise it (together with CONFIG_NET_IF_MAX_IPV6_COUNT and the number of zephyr,native-tap interfaces in boards/native_sim.overlay) to delegate to more links.

The server build (overlay-server.conf) uses a single interface named zeth: overlay-server.overlay, disables the downstream interface and renames the remaining one, so that build attaches to zeth rather than zeth0.

To give the TAP interfaces host-side connectivity, set them up with the net-setup.sh script from the net-tools project before running, e.g. one instance as the server and another as the requesting router. See README-dhcpv6-pd.md file in net-tools for details.

Building and Running

Requesting router (client):

west build -b native_sim samples/net/dhcpv6_pd
west build -t run

Delegating router (server):

west build -b native_sim samples/net/dhcpv6_pd -- \
    -DEXTRA_CONF_FILE=overlay-server.conf \
    -DEXTRA_DTC_OVERLAY_FILE=overlay-server.overlay
west build -t run

Requirements

The requesting-router downstream advertisement requires CONFIG_NET_IPV6_ND_RA_TX and, for forwarding between the WAN and LAN interfaces, CONFIG_NET_IPV6_FORWARDING.

See also

DHCPv6
DHCPv6 server