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I have a linux server that needs to get some routing. I'm fairly new at this and i don't find any clear source on google.

The setup should be simple:
All traffic to a server on ip 192.168.72.20 should be sent over interface 3. All other interfaces don't matter at the moment.

Here you have the output for route -n

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.72.0    0.0.0.0         255.255.255.0   U     0      0        0 eth0
192.168.72.0    0.0.0.0         255.255.255.0   U     0      0        0 eth1
192.168.72.0    0.0.0.0         255.255.255.0   U     0      0        0 eth2
192.168.72.0    0.0.0.0         255.255.255.0   U     0      0        0 eth3
192.168.72.0    0.0.0.0         255.255.255.0   U     0      0        0 eth4
169.254.0.0     0.0.0.0         255.255.0.0     U     1002   0        0 eth0
0.0.0.0         192.168.72.12   0.0.0.0         UG    0      0        0 eth0
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    Are you using the old fashioned ifconfig and route command or the modern ip commands? (old ones would be something like route add -host 192.168.72.20 GW eth3_ip) – Hennes Mar 29 '13 at 13:48
  • i don't know, i guess the old ones, how can i check that? – Frederiek Mar 29 '13 at 13:58
23

Try:

ip route add 192.168.72.20/32 dev eth3

| improve this answer | |
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    Just a note: to permanently keep this configuration make sure you add it to /etc/rc.local or your distro's equivalent. It won't persist between reboots. – LawrenceC Mar 29 '13 at 16:32
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    I tried this same format for mapping an IP to the wlan0 on Ubuntu 14.04 and got RTNETLINK answers: Invalid argument I had to remove the /** from the IP so I ended up with: sudo ip route add 192.168.50.15 dev wlan0 -- thought I'd mention that in case anyone else ran into this issue. Thank you for your answer ultrasawblade, it was helpful. – mason81 Jul 10 '15 at 14:54
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    Do not forget via <gateway_ip> if the target IP is not directly reachable! – calandoa Dec 4 '17 at 15:00
  • How would I add another entry saying "use this interface for all other destination IPs"? – holzkohlengrill Jul 29 at 12:51
  • That's called setting a default gateway and is done with ip route add default via $ROUTER_IP dev $INTERFACE. – LawrenceC Jul 29 at 15:57

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