To make my Ubuntu Server on more robust I have connected it to 2 ISP so that I can have redundant last mile. Also one of my ISP gives me unlimited bandwidth while the other is costlier but more reliable.
1. To make your linux server multihomed, I am assuming that you have atleast 2 network interfaces. In my case both are ethernet (eth0 and eth1)
2. Make sure both the networks are working individually up by setting it on
sudo vi /etc/network/interface
#Loopback auto lo iface lo inet loopback # The primary network interface auto eth0 iface eth0 inet static address 192.168.200.100 netmask 255.255.255.0 metric 100 gateway 192.168.200.6 auto eth1 iface eth1 inet static address 192.168.201.100 netmask 255.255.255.0 metric 200 gateway 192.168.201.5Now if you go to your terminal, you should be able to
>ip route show 192.168.201.0/24 dev eth1 proto kernel scope link src 192.168.201.100 192.168.200.0/24 dev eth0 proto kernel scope link src 192.168.200.100 default via 192.168.200.6 dev eth0 metric 100 default via 192.168.201.5 dev eth1 metric 200With this if your eth0 goes down, your eth1 will take over and vice-versa. But this is still a long way from making your network multihoned where your can do load balancing.
All you need to do is to add multihop route in your /etc/rc.local ip route append default scope global nexthop via 192.168.200.6 dev eth0 weight 5 nexthop via 192.168.201.5 dev eth1 weight 1
A common configuration is the following, in which there are two providers that connect a local network (or even a single machine) to the big Internet.
________ +------------+ / | | | +-------------+ Provider 1 +------- __ | | | / ___/ \_ +------+-------+ +------------+ | _/ \__ | if1 | / / \ | | | | Local network -----+ Linux router | | Internet \_ __/ | | | \__ __/ | if2 | \ \___/ +------+-------+ +------------+ | | | | \ +-------------+ Provider 2 +------- | | | +------------+ \________There are usually two questions given this setup.
The first is how to route answers to packets coming in over a particular provider, say Provider 1, back out again over that same provider.
Let us first set some symbolical names. Let eth2 be the name of the first interface (if1 in the picture above) and eth2 the name of the second interface. Then let IP1 be the IP address associated with eth2 and IP2 the IP address associated with eth2. Next, let GW1 be the IP address of the gateway at Provider 1, and GW2 the IP address of the gateway at provider 2. Finally, let NET1 be the IP network GW1 is in, and NET2 the IP network GW2 is in.
One creates two additional routing tables, say T1 and T2. These are added in /etc/iproute2/rt_tables. Then you set up routing in these tables as follows:
ip route add NET1 dev eth1 src IP1 table T1 ip route add default via GW1 table T1 ip route add NET2 dev eth2 src IP2 table T2 ip route add default via GW2 table T2
You must create the tables in the file: '/etc/iproute2/rt_tables'
# # reserved values # 255 local 254 main 253 default 0 unspec # # local # #1 inr.ruhep 1 internal <<--- These lines were added to the default file 2 WAN2 <<--- they define the table by name and number 3 WAN1 <<--- Table 1 is named 'internal' and so on.More information about rt_tables can be found here: http://www.rjsystems.nl/en/2100-adv-routing.php Nothing spectacular, just build a route to the gateway and build a default route via that gateway, as you would do in the case of a single upstream provider, but put the routes in a separate table per provider. Note that the network route suffices, as it tells you how to find any host in that network, which includes the gateway, as specified above.
Next you set up the main routing table. It is a good idea to route things to the direct neighbour through the interface connected to that neighbour. Note the `src' arguments, they make sure the right outgoing IP address is chosen.
ip route add NET1 dev eth2 src IP1 ip route add NET2 dev eth2 src IP2
Then, your preference for default route:
ip route add default via GW1
Next, you 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:
ip rule add from IP1 table T1 ip rule add from IP2 table T2
This set of commands makes sure all answers to traffic coming in on a particular interface get answered from that interface.
Reader Rod Roark notes: If NET0 is the local network and eth0 is its interface, the following additional entries are desirable: ip route add NET0 dev eth0 table T1 ip route add NET2 dev eth2 table T1 ip route add 127.0.0.0/8 dev lo table T1 ip route add NET0 dev eth0 table T2 ip route add NET1 dev eth2 table T2 ip route add 127.0.0.0/8 dev lo table T2
Now, this is just the very basic setup. It will work for all processes running on the router itself, and for the local network, if it is masqueraded. If it is not, then you either have IP space from both providers or you are going to want to masquerade to one of the two providers. In both cases you will want to add rules selecting which provider to route out from based on the IP address of the machine in the local network.
The second 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, you now 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):
ip route add default scope global nexthop via GW1 dev eth2 weight 1 \ nexthop via GW2 dev eth2 weight 1
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.
Furthermore, if you really want to do this, you probably also want to look at Julian Anastasov's patches at http://www.ssi.bg/~ja/#routes , Julian's route patch page. They will make things nicer to work with.