On 2019-12-11 10:10:17 +0100 (+0100), Ignazio Cassano wrote:
[...]
> Dec 11 09:49:06 podto2-osctrl01 dnsmasq-dhcp[70093]: cannot send
>     DHCP/BOOTP option 121: no space left in packet
[...]

This error is fairly straightforward. DHCP replies are limited to
what you can fit in a single UDP packet and how large of a datagram
the client agrees to accept. The number of routes you're trying to
include in via option 121 could be the problem (is it a bunch?) but
also the other fields and their lengths can also contribute, as can
the MTU on that network segment:

    https://tools.ietf.org/html/rfc2131

According to IETF RFC 2131 you should be able to assume clients will
accept a datagram of up to 576 octets in length (which implies your
entire options field can use at least 312 octets). Anything over
this requires negotiation of a maximum DHCP message size with the
client.
--
Jeremy Stanley