Embedded DHCP/DHCPv6/RA Server & Relay
odhcpd is a daemon for serving and relaying IP management protocols to configure clients and downstream routers. It tries to follow the RFC 6204 requirements for IPv6 home routers.
odhcpd provides server services for DHCP, RA, stateless and stateful DHCPv6, prefix delegation and can be used to relay RA, DHCPv6 and NDP between routed (non-bridged) interfaces in case no delegated prefixes are available.
1. Router Discovery support (solicitations and advertisements) with 2 modes
server: RD server for slave interfaces a) automatic detection of prefixes, delegated prefix and default routes, MTU b) automatic reannouncement when changes to prefixes or routes occur
relay: RD relay between master and slave interfaces a) support for rewriting announced DNS-server addresses in relay mode
2. DHCPv6-support with 2 modes of operation
server: stateless, stateful and PD-server mode a) stateless and stateful address assignment b) prefix delegation support c) dynamic reconfiguration in case prefixes change d) hostname detection and hosts-file creation
relay: mostly standards-compliant DHCPv6-relay a) support for rewriting announced DNS-server addresses
server: stateless and stateful mode
4. Proxy for Neighbor Discovery messages (solicitations and advertisments)
a) support for auto-learning routes to the local routing table b) support for marking interfaces "external" not proxying NDP for them and only serving NDP for DAD and for traffic to the router itself [Warning: you should provide additional firewall rules for security]
odhcpd uses cmake:
odhcpd uses a UCI configuration file in /etc/config/dhcp for configuration and may also receive information from ubus
Section of type odhcpd Option Type Default Description legacy bool 0 Enable DHCPv4 if start but no dhcpv4 option set leasefile string DHCP/v6 lease/hostfile leasetrigger string Lease trigger script Sections of type dhcp (configure DHCP / DHCPv6 / RA / NDP service) Option Type Default Description interface string <name of UCI section> logical OpenWrt interface ifname string <resolved from logical> physical network interface networkid string same as ifname compat. alias for ifname ignore bool 0 do not serve this interface unless overridden by ra, ndp, dhcpv4 or dhcpv6 options master bool 0 is a master interface for relaying ra string disabled Router Advert service [disabled|server|relay|hybrid] dhcpv6 string disabled DHCPv6 service [disabled|server|relay|hybrid] dhcpv4 string disabled DHCPv4 service [disabled|server] ndp string disabled Neighbor Discovery Proxy [disabled|relay|hybrid] dynamicdhcp bool 1 dynamically create leases for DHCPv4 and DHCPv6 dns list <local address> DNS servers to announce accepts IPv4 and IPv6 domain list <local search domain> Search domains to announce leasetime string 12h DHCPv4 address leasetime start integer 100 DHCPv4 pool start limit integer 150 DHCPv4 pool size ra_default integer 0 Override default route 0: default 1: ignore no public address 2: ignore all ra_management integer 1 RA management mode 0: no M-Flag but A-Flag 1: both M and A 2: M but not A ra_offlink bool 0 Announce prefixes off-link ra_preference string medium Route(r) preference [medium|high|low] ra_maxinterval integer 600 Maximum time allowed between sending unsolicited RA ra_mininterval integer 200 Minimum time allowed between sending unsolicited RA ra_lifetime integer 1800 Value to be placed in Router Lifetime field of RA ra_useleasetime bool 0 Use configured leasetime as limit for the preferred and valid lifetime of a prefix ra_reachabletime integer 0 Reachable Time in milliseconds to be advertised in RA messages ra_retranstime integer 0 Retransmit Time in milliseconds to be advertised in RA messages ra_hoplimit integer 0 Current hoplimit to be advertised in RA messages ra_mtu integer 0 MTU to be advertised in RA messages ndproxy_routing bool 1 Learn routes from NDP ndproxy_slave bool 0 NDProxy external slave ndproxy_static list Static NDProxy prefixes Sections of type host (static leases) Option Type Default Description ip string IP-Address to lease mac string MAC-address duid string DUID in base16 hostid string IPv6 host identifier name string Hostname
ubus -v list ubus -v list dhcp ubus call dhcp ipv4leases ubus call dhcp ipv6leases
On a default OpenWrt 14.07 install, odhcpd can log many messages to the syslog (viewable with “logread”) of the form:
Tue Oct 7 14:15:41 2014 daemon.warn odhcpd: DHCPV6 SOLICIT IA_NA from (long hex number) on br-lan: no addresses available
If IPv6 DHCP is needed, avoid these messages by…
If IPv6 DHCP is not being used at all, odhcpd can have DHCPv6 disabled to avoid these messages.
# get the current setting for dhcpv6 in /etc/config/dhcp uci get dhcp.lan.dhcpv6
The default value is “server”.
Disable dhcpv6 and commit the change.
uci set dhcp.lan.dhcpv6=disabled uci commit
Confirm the new value is “disabled”.
uci get dhcp.lan.dhcpv6
Now restart odhcpd (or just reboot the router).