odhcpd - Embedded DHCP/DHCPv6/RA Server & Relay

** Abstract **

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.


** Features **

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
   
3. DHCPv4-support
   server: stateless and stateful mode

4. Proxy for Neighbor Discovery messages (solicitations and advertisements)
   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]


** Compiling **

odhcpd uses cmake:
* To prepare a Makefile use:  "cmake ." 
* To build / install use: "make" / "make install" afterwards.
* To build DEB or RPM packages use: "make package" afterwards.


** Configuration **

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
maindhcp	bool	0			Use odhcpd as the main DHCPv4
						service
leasefile	string				DHCP/v6 lease/hostfile
leasetrigger	string				Lease trigger script
loglevel	integer 6			Syslog level priority (0-7)


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
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
dhcpv4_forcereconf	bool	0			Force reconfiguration by sending
							force renew message even if the client
							did not include the force renew nonce
							capability option (RFC6704)
dhcpv6_assignall	bool	1			Assign all viable DHCPv6 addresses
							in statefull mode; if disabled
							only the DHCPv6 address having the
							longest preferred lifetime is assigned
dhcpv6_hostidlength	integer 12			Host ID length of dynamically created leases,
							allowed values: 12 - 64 (bits).
dhcpv6_na		bool	1			DHCPv6 stateful addressing hands out IA_NA -
								Internet Address - Network Address
dhcpv6_pd		bool	1			DHCPv6 stateful addressing hands out IA_PD -
								Internet Address - Prefix Delegation
router			list    <local address>		Routers to announce
							accepts IPv4 only
dns			list	<local address>		DNS servers to announce
							accepts IPv4 and IPv6
dns_service		bool	1			Announce the address of interface as DNS service
							if the list of dns is empty
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
preferred_lifetime	string	12h			Value for the preferred lifetime
							for a prefix
ra_default		integer	0			Override default route
			0: default, 1: ignore no public address, 2: ignore all
ra_flags		list	other-config		List of RA flags to be
							advertised in RA messages
			[managed-config other-config home-agent none]
ra_slaac		bool	1			Announce slaac for a prefix
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 -			MTU to be advertised in
							RA messages
ra_dns			bool	1			Announce DNS configuration in
							RA messages (RFC8106)
ra_pref64		string				Announce PREF64 option
			[IPv6 prefix]			for NAT64 prefix (RFC8781)
ndproxy_routing		bool	1			Learn routes from NDP
ndproxy_slave		bool	0			NDProxy external slave
prefix_filter		string	::/0			Only advertise on-link prefixes within
			[IPv6 prefix]			the provided IPv6 prefix; others are
							filtered out.
ntp			list	<local address>		NTP servers to announce
							accepts IPv4 and IPv6


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
leasetime	string				DHCPv4/v6 leasetime