Load Balancing for sharing multiple internet connections
Overview
We have three Internet connection from three different ISP.
Due to hardware limitation we have connected two ISP line connected to one PC.
Details regarding to Interface is-
etho -192.168.0.X
eth1- A.B.C.D
ppp0- W.X.Y.Z
Why Load Balancing ?
The main purpose of load balancing is to share multiple Internet connection from different service provider for maximum utilization of bandwidth. We try to achieve this goal by two method
A) Load Balancing by using EQL interface-
EQL is serial line load balancer which is kernel module. by which we can enslave or tie multiple serial line from different or same provider. But the condition is that this line should be connected through modem. Which is not suitable for us.
B) Load Balancing by IP tables and Routing-
There are many places where a Linux based router/masquerading device can assist in managing multiple Internet connections. We’ll outline here some of the more common setups involving multiple Internet connections and how to manage them with iptables and routing. One of the first distinctions you can make when planning how to use multiple Internet connections is what inbound services you expect to host and how you want to split traffic over the multiple links.
Step by step implementation
When we are using single connection from one ISP in such case our default route will me in ‘main’ routing table of kernel. Now in our case we have connected two connection to proxy server out of that one line is from ‘pacenet’ and other is from ‘sify’. As we have not implemented load balancing the default router in ‘main’ table of kernel will be either fro sify or pacenet.
[1] How it works
Lets us check our ‘main’ routing table ….
magnet@proxy:~$ ip route show table main
25.X.X.X dev ppp0 proto kernel scope link src W.X.Y.Z
192.168.0.X/24 dev eth0 proto kernel scope link src 192.168.0.X
10.X.X.X/24 dev eth1 proto kernel scope link src A.B.C.D
default dev ppp0 scope link
magnet@proxy:~$
root@proxy:~# ip route show table main
25.X.X.X dev ppp0 proto kernel scope link src W.X.Y.Z
192.168.0.X/24 dev eth0 proto kernel scope link src 192.168.0.X
10.X.X.X/24 dev eth1 proto kernel scope link src A.B.C.D
default via 10.X.X.X dev eth1
root@proxy:~#
To use both the line effectively we need to create to two new routing table. So that we can provide default gateway in each routing table separately.
Step [1]
First step in load balancing is to create separate routing table for each connection. Lets create table.
root@proxy:~# tail /etc/iproute2/rt_tables
253 sify3
252 sify192
251 pacenet
root@proxy:~#
Whenever we want to create new routing table we need to add entries in above file.
step [2]
Now we will add routing details in this table
root@proxy:~# ip route add 25.X.X.X dev ppp0 src W.X.Y.Z proto kernel scope link table pacenet
root@proxy:~# ip route add default via 25.X.X.X table pacenet
root@proxy:~# ip route show table pacenet
25.X.X.X dev ppp0 proto kernel scope link src W.X.Y.Z
default via 25.X.X.X dev ppp0
root@proxy:~#
As shown above we have created separate routing table ‘pacenet’ for pacenet connection. With default gateway 25.X.X.X and interface ppp0.
Similarly we have created separate routing table ‘sify3’ for sify connection. with defalut gateway 10.X.X.X and interface eth1.
root@proxy:~# ip route add 10.X.X.X/24 dev eth1 src A.B.C.D proto kernel scope link table sify3
root@proxy:~# ip route add default via 10.X.X.X table sify3
root@proxy:~# ip route show table sify3
10.X.X.X/24 dev eth1 proto kernel scope link src A.B.C.D
default via 10.X.X.X dev eth1
root@proxy:~#
step [3]
One more thing we left here is that we have to add entries for local network in both table. This is basic setup for separating routing decision for both provider.
root@proxy:~# ip route add 192.168.0.X/24 dev eth0 proto kernel scope link src 192.168.0.X table sify3
root@proxy:~# ip route add 192.168.0.X/24 dev eth0 proto kernel scope link src 192.168.0.X table pacenet
Finally we will check entries in each routing table
root@proxy:~# ip route show table sify3
192.168.0.X/24 dev eth0 proto kernel scope link src 192.168.0.X
10.X.X.X/24 dev eth1 proto kernel scope link src A.B.C.D
default via 10.X.X.X dev eth1
root@proxy:~# ip route show table pacenet
25.X.X.X dev ppp0 proto kernel scope link src W.X.Y.Z
192.168.0.X/24 dev eth0 proto kernel scope link src 192.168.0.X
default via 25.X.X.X dev ppp0
root@proxy:~#
step [4]
Next, we will set up the routing rules. These actually choose what routing table to route with. You want to make sure that you route out a given interface if you already have the corresponding source address:
root@proxy:~# ip rule add from W.X.Y.Z table pacenet
root@proxy:~# ip rule add from A.B.C.D table sify3
Here W.X.Y.Z is the static IP assign to ppp0 interface. The first rule tells to kernel that use table ‘pacenet’ to route all the pkts going out of interface ppp0 similarly for sify connection.
Step [5] Now delete default route in ‘main’ table.
root@proxy:~# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
25.X.X.X 0.0.0.0 255.255.255.255 UH 0 0 0 ppp0
192.168.0.X 0.0.0.0 255.255.255.0 U 0 0 0 eth0
10.X.X.X 0.0.0.0 255.255.255.0 U 0 0 0 eth1
0.0.0.0 10.X.X.1 0.0.0.0 UG 0 0 0 eth1
root@proxy:~# route del default
root@proxy:~# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
25.1.1.2 0.0.0.0 255.255.255.255 UH 0 0 0 ppp0
192.168.0.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
10.10.127.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1
root@proxy:~# ip route show
25.1.1.2 dev ppp0 proto kernel scope link src 203.115.69.16
192.168.0.0/24 dev eth0 proto kernel scope link src 192.168.0.3
10.10.127.0/24 dev eth1 proto kernel scope link src 10.10.127.222
Step [6]
Now the question is how to balance traffic going out over the two providers. This is actually not hard if you already have set up split access as above. Instead of choosing one of the two providers as your default route,We will set up the default route to be a multipath route. In the default kernel this will balance routes over the two providers. It is done as follows (once more building on the example in the section on split-access):
root@proxy:~# ip route add default nexthop via 10.X.X.1 dev eth1 weight 1 nexthop via W.X.Y.Z dev ppp0 weight 1
root@proxy:~# ip route show
25.X.X.X dev ppp0 proto kernel scope link src W.X.Y.Z
192.168.0.X/24 dev eth0 proto kernel scope link src 192.168.0.X
10.X.X.X/24 dev eth1 proto kernel scope link src A.B.C.D
default
nexthop via A.B.C.D dev eth1 weight 1
nexthop via W.X.Y.Z dev ppp0 weight 1
root@proxy:~#
This will balance the routes over both providers. The weight parameters can be tweaked to favor one provider over the other.
Note that balancing will not be perfect, as it is route based, and routes are cached. This means that routes to often-used sites will always be over the same provider.
Thank you
Arun Bagul
Reference URL:–
http://linux-ip.net/html/index.html
http://linux-ip.net/html/ch-advanced-routing.html
http://lartc.org/howto/lartc.rpdb.html
http://lartc.org/howto/lartc.rpdb.multiple-links.html
http://www.shorewall.net/