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I have Ubuntu Server 12.04

I have 3 gateways on my lan

Ubuntu has 3 NICs

eth0 gw
eth1 gw
eth2 gw

If a request comes in from gw it work fine. the other gateways don't

I have tried to fix this with routes but I can't seem to get it right.

My ISP can only give 10Mbps up per modem the server streams a live video feed. I need all 3 modems for load balancing

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface         UG    100    0        0 eth0   U     0      0        0 eth1   U     0      0        0 eth2   U     0      0        0 eth0

If this could be done with one NIC I am fine with that I just need to be able to balance this traffic.

I tried this (but all networking stopped after):

#echo "60 out60" >> /etc/iproute2/rt_tables
#echo "61 out61" >> /etc/iproute2/rt_tables
#echo "62 out62" >> /etc/iproute2/rt_tables

#ip route add default via table out60
#ip route add default via table out61
#ip route add default via table out62

#ip rule add from table out60
#ip rule add from table out61
#ip rule add from table out62

This Diagram doesn't have the server in question its just so you can see the network layout.

Network Diagram
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Why do you have three gateways for a web server? – Joel E Salas Aug 9 '13 at 2:46
Wut... where is all the traffic going? Why three gateways? – ewwhite Aug 9 '13 at 2:47
My ISP can only give 10Mbps up per modem the server streams a live video feed. I need all 3 modems for load balancing. – Eric Fluharty Aug 9 '13 at 2:50
What does you routing table look like? You might have to configure each one to be on a separate subnet. – Ryan Gibbons Aug 9 '13 at 4:14
This network is in a production environment. I can't change the design of the network, only the server its self. – Eric Fluharty Aug 9 '13 at 6:05

2 Answers 2

I will strongly recommend to change subnet. It's very bad idea to use the same subnet for all interfaces and their gateways, imho

I would suggest to use something like the following

eth0 gw
eth1 gw
eth2 gw

You could try to setup PBR, but I don't know, if it would work in your environment





/sbin/ip route add $P1_NET dev $IF1 src $IP1 table ISP1
/sbin/ip route add default via $GW1 table ISP1

/sbin/ip route add $P2_NET dev $IF2 src $IP2 table ISP2
/sbin/ip route add default via $GW2 table ISP2

/sbin/ip route add $P3_NET dev $IF3 src $IP3 table ISP3
/sbin/ip route add default via $GW3 table ISP3

/sbin/ip rule add from $IP1 table ISP1
/sbin/ip rule add from $IP2 table ISP2
/sbin/ip rule add from $IP3 table ISP3

/sbin/ip route add default via $P1
/sbin/ip route flush cache

Don't forget to enable ip forwarding and disable Reverse Path Filtering

# echo 1 > /proc/sys/net/ipv4/ip_forward
# echo 0 > /proc/sys/net/ipv4/conf/default/rp_filter
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I can not modify the network. I have many other production systems running on this network. – Eric Fluharty Aug 9 '13 at 23:40
I will try this again, but last I tried it broke networking. – Eric Fluharty Aug 9 '13 at 23:54
$ sudo ip route add dev eth0 src table ISP1 RTNETLINK answers: Invalid argument – Eric Fluharty Aug 10 '13 at 1:03
I removed the scr field from this command, it ran successfully but didn't work in the end # ip route add dev eth2 table ISP3 – Eric Fluharty Aug 10 '13 at 1:23
Did you add ISP1/ISP2/ISP3 to the /etc/iproute2/rt_tables ? – ALex_hha Aug 10 '13 at 6:36

The confusion expressed in the comments stems from this Private Class A LAN networking scheme being not very conventional or common in practice. Usually each net block is (a /28,/16 etc.) is broken up and the gateway set to the first usable IP. In this case it looks like each modem is a /31.

Paste output of route -n or netstat -nra (should work on most *nix variants) if you're interested as to what gateway each interface believes it has, for further diagnosis.

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