How can I configure my DHCP server to distribute IP routes?

Question

I have a DHCP server (Linux, IPCop, dnsmasq) running on my default gateway server 192.168.0.1. I have a VPN endpoint on another server in the network (192.168.0.4). Is it possible to configure the DHCP server so it sends not only the default gateway but also routing information for the VPN (192.168.1.*) to DHCP clients when they request an IP address? The DHCP clients run Windows and Linux.

I tried to find something in the official documentation (http://www.ipcop.org/2.0.0/en/admin/html/custom-dnsmasq-local.html) but failed. The existence of RFC3442 indicates that it might be possible somehow.

http://jcape.name/2009/07/17/distributing-static-routes-with-dhcp/ — HopelessN00b, Oct 29 '14 at 15:39
From the link it is not obvious to me what to put in `dnsmasq.local`. — blerontin, Oct 29 '14 at 16:20

score 10 · Accepted Answer · edited Oct 07 '21 at 06:58

This can be done by adding the following lines to dhcpd.conf:

option rfc3442-classless-static-routes code 121 = array of integer 8;
option rfc3442-classless-static-routes 24, 192, 168, 1, 192, 168, 0, 4;
option ms-classless-static-routes code 249 = array of integer 8;
option ms-classless-static-routes 24, 192, 168, 1, 192, 168, 0, 4;

This distributes a route entry for network 192.168.1.0/24 using the gateway 192.168.0.4.

The meaning of the bytes is (in brackets the value from the example above):

WW, D1, D2, D3, R1, R2, R3, R4
WW      = destination network mask width (24)
D1..D3  = destination network address (192.168.1.*)
R1..R4  = router address (192.168.0.4)

Note: The number of D1..DN bytes varies depending on the network mask. See RFC3442 for details.

confused - pretty sure that the OP specifies dnsmasq as the server — nhed, Jan 18 '17 at 16:49
pretty extensive explanation on how it works: https://serverfault.com/a/575936/155358 — Benedikt Köppel, Aug 08 '17 at 14:28

How can I configure my DHCP server to distribute IP routes?

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