[OpenWrt-Devel] dnsmasq and --dhcp-relay option ?

openwrt-devel at couprie.net openwrt-devel at couprie.net
Thu Apr 23 16:55:57 EDT 2015


I need the dnsmasq --dhcp-relay option, how do i add this option to the 
dnsmasq script ?


--dhcp-relay=<local address>,<server address>[,<interface] Configure 
dnsmasq to do DHCP relay. The local address is an address allocated to 
an interface on the host running dnsmasq. All DHCP requests arriving on 
that interface will we relayed to a remote DHCP server at the server 
address. It is possible to relay from a single local address to multiple 
remote servers by using multiple dhcp-relay configs with the same local 
address and different server addresses. A server address must be an IP 
literal address, not a domain name. In the case of DHCPv6, the server 
address may be the ALL_SERVERS multicast address, ff05::1:3. In this 
case the interface must be given, not be wildcard, and is used to direct 
the multicast to the correct interface to reach the DHCP server.

Access control for DHCP clients has the same rules as for the DHCP 
server, see --interface, --except-interface, etc. The optional interface 
name in the dhcp-relay config has a different function: it controls on 
which interface DHCP replies from the server will be accepted. This is 
intended for configurations which have three interfaces: one being 
relayed from, a second connecting the DHCP server, and a third untrusted 
network, typically the wider internet. It avoids the possibility of 
spoof replies arriving via this third interface.

It is allowed to have dnsmasq act as a DHCP server on one set of 
interfaces and relay from a disjoint set of interfaces. Note that whilst 
it is quite possible to write configurations which appear to act as a 
server and a relay on the same interface, this is not supported: the 
relay function will take precedence.

Both DHCPv4 and DHCPv6 relay is supported. It's not possible to relay 
DHCPv4 to a DHCPv6 server or vice-versa.
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