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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 and 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

Router Discovery (RD)

Router Discovery (RD) support (solicitations and advertisements) with 2 modes of operation:

  1. RD Server mode: Router Discovery (RD) server for slave interfaces:
    1. Automatic detection of prefixes, delegated prefix, default routes and MTU.
    2. Automatic re-announcement of any changes in either prefixes or routes.
  2. RD Relay mode: Router Discovery (RD) relay between master and slave interfaces.
    1. Supports rewriting of the announced DNS server addresses.

DHCPv6

DHCPv6 support with 2 modes of operation:

  1. DHCPv6 Server mode: stateless, stateful and Prefix Delegation (PD) server mode:
    1. Stateless and stateful address assignment.
    2. Prefix delegation support.
    3. Dynamic reconfiguration of any changes in Prefix Delegation.
    4. Hostname detection and hosts-file creation.
  2. DHCPv6 Relay mode: A mostly standards-compliant DHCPv6-relay:
    1. Supports rewriting of the announced DNS server addresses.

DHCPv4

  1. Stateless and stateful DHCPv4 server mode.

Neighbor Discovery Proxy (NDP)

Proxy for Neighbor Discovery solicitation and advertisement messages (NDP):

  1. Supports auto-learning of routes to the local routing table.
  2. Supports marking interfaces as “external”.

Interfaces marked as “external” will not receive any proxyied NDP content and are only served with NDP for Duplicate Address Detection (DAD) and traffic to the router itself.

:!: Interfaces marked as external need additional firewall rules for security!

Configuration

odhcpd uses a UCI configuration file in /etc/config/dhcp for configuration and may also receive information from ubus.

odhcpd section

Configuration for the odhcp daemon.

Name Type Default Description
legacy boolean 0 Enable DHCPv4 if the 'dhcp' section constains a start option, but no dhcpv4 option set.
leasefile string Location of the lease/hostfile for DHCPv4 and DHCPv6.
leasetrigger string Location of the lease trigger script.

dhcp section

Configuration for DHCPv4, DHCPv6, RA and NDP services.

Name Type Required Default Description
interface string <name of UCI section> Logical OpenWrt interface.
ifname string <resolved from logical> Physical network interface.
networkid string <same as ifname> Alias of ifname for compatibility.
ignore boolean 0 do not serve this interface unless overridden by ra, ndp, dhcpv4 or dhcpv6 options.
master boolean 0 is a master interface for relaying
ra string disabled Router Advert service. Set to disabled, server, relay or hybrid.
dhcpv6 string disabled DHCPv6 service. Set to disabled, server, relay or hybrid.
dhcpv4 string disabled DHCPv4 service. Set to disabled or server.
ndp string disabled Neighbor Discovery Proxy. Set to disabled, relay or hybrid.
dynamicdhcp boolean 1 Leases for DHCPv4 and DHCPv6 are created dynamically.
dns list <local address> DNS servers to announce on the network. IPv4 and IPv6 addresses are accepted.
domain list <local search domain> Search domains to announce on the network.
leasetime string 12h DHCPv4 address leasetime
start integer 100 Starting address of the DHCPv4 pool.
limit integer 150 Number of addresses in the DHCPv4 pool.
ra_default integer 0 Override default route- Set to 0 (default), 1 (ignore, no public address) or 2 (ignore all).
ra_management integer 1 RA management mode. See the “RA Management Modes” table below.
ra_offlink boolean 0 Announce prefixes off-link
ra_preference string medium Route preference medium, high or low
ra_maxinterval integer 600 Maximum time allowed between sending unsolicited Router Advertisements (RA).
ra_mininterval integer 200 Minimum time allowed between sending unsolicited Router Advertisements (RA).
ra_lifetime integer 1800 Router Lifetime published in Router Advertisement (RA) messages.
ra_useleasetime boolean 0 If set, the configured DHCPv4 leasetime is also used as limit and preferred lifetime of the IPv6 prefix.
ra_reachabletime integer 0 Reachable Time in milliseconds to be published in Router Advertisement (RA) messages'.
ra_retranstime integer 0 Retransmit Time in milliseconds to be published in Router Advertisment (RA) messages.
ra_hoplimit integer 0 The maximum hops to be published in Router Advertisement (RA) messages.
ra_mtu integer 0 The MTU to be published in Router Advertisement (RA) messages.
ra_dns boolean 1 Announce DNS configuration in RA messages (RFC8106).
ndproxy_routing boolean 1 Learn routes from ND.P
ndproxy_slave boolean 0 NDProxy external slave.
ndproxy_static list Static NDProxy prefixes.

RA management modes

Mode M Flag A Flag Description
0 No Yes Only stateless (SLAAC) configuration enabled.
1 Yes Yes Both stateless (SLAAC) and stateful (DHCPv6) configurations are enabled.
2 Yes No Only statefull (DHCPv6) configuration is enabled.

host section

The host section is where static leases are defined.

Name Type Required Default Description
ip string Yes None IP-Address to lease
mac string Optional None MAC-address
duid string No None DUID in base16
hostid string No None IPv6 host identifier
name string No None Hostname

ubus API

Replace dnsmasq with odhcpd to access IPv4 leases. 

ubus -v list dhcp
ubus call dhcp ipv4leases
ubus call dhcp ipv6leases

Compiling

odhcpd uses cmake. 

# Prepare
cmake .
 
# Build/install
make
make install
 
# Build DEB/RPM packages
make package

Documentation

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  • Last modified: 2021/05/01 23:48
  • by vgaetera