I have a server H with two NICs with ip address 192.168.105.10 and 192.168.104.10. An application running on H receives data from server C on UDP port 1703. Server C IP address is 192.168.105.14
I want to duplicate the incoming UDP packets and send them to server D, where another application listens on 192.168.104.11 also on port 1703.
H runs debian 11 (kernel 5.10). So far I have the following NFT table setup on H:
#!/sbin/nft -f table ip route_C_packets delete table ip route_C_packets table ip route_C_packets { chain C_in { type filter hook prerouting priority 0; policy accept; ip saddr "192.168.105.14" udp port 1703 ip daddr set "192.168.104.11" dup to "192.168.104.11" ip daddr set "192.168.105.10" } } This works, however it seems a bit ugly. From my understanding:
ip saddr "192.168.105.14" udp port 1703: filter only UDP packets from C on the port I am interested in
ip daddr set "192.168.104.11: overrides the destination address (so that the application running on D can actually receive them)
dup_to "192.168.104.11": duplicates the packet and sends it to D, but does not modify daddr by itself
ip daddr set "192.168.105.10": restores the original destination address for the non duplicated packet so that the application running on H can actually receive it.
This trick of changing daddr and then restoring it back seems wrong to me, is there any syntax to set daddr on the duplicated packet rather than on the original one?
EDIT: Everything here has netmask 255.255.255.0. 168.105 and 168.104 are effectively two segregated networks.
