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More development on dhcp-split-relay.

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Simon Kelley
2025-08-20 12:36:03 +01:00
parent ff30fa4b91
commit 1677c6e10b
6 changed files with 215 additions and 159 deletions
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9
man/dnsmasq.8
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@@ -1489,19 +1489,22 @@ prefix-delegation from relayed DHCP transactions. See
.B --dhcp-script
for details.
.TP
.B --dhcp-split-relay=<local address>,[<server address>[#<server port>]],<server-facing-interface>
.B --dhcp-split-relay=<local address>,[<server address>[#<server port>]],<server-facing-interface>|<server-facing-address>
A usefully enchanced version of DHCPv4 relay. IPv4 DHCP normally uses a single address
for two functions; it is used by the DHCP server to determine which network to allocate
an address on, and it is used as the address of the relay to which the server sends packets.
This version of DHCP relay splits these functions. It uses the address of the server-facing relay
interface as the address that the server talks to. The address of the client-facing interface
interface or a directly-specified address as the address that the server talks to. The address of the client-facing interface
(the first item in the config) is used as to determine the client's subnet. The
local address is also used as server-ID override so that the client always sends requests
via the relay. The effect of this is that server doesn't require
a route to the client network and the clients don't require a route to the server.
The interface parameter is mandatory and a cannot be a wildcard.
The third parameter is mandatory. If it is an interface name it cannot be a wildcard and the same filtering as descibed in
--dhcp-relay applies; answers from the server must arrve via the specified interface. If the third parameter
is an IP address it must be an address of a local interface which is routable from the server; In this case no filtering
is done, the reply packets can arrive via any route.
If setting up a network where the client networks have limited routing, be careful
about configuring the DHCP server. Dnsmasq, as DHCP server, will set the default route to the