# sysctl -w net.ipv4.conf.all.arp_filter=1
# echo "net.ipv4.conf.all.arp_filter = 1" >> /etc/sysctl.conf 2. Configure /etc/network/interfaces as following:
# The loopback network interface
auto lo
iface lo inet loopback
auto eth0
iface eth0 inet static
address 7.7.7.4
network 7.7.7.0
netmask 255.255.255.0
broadcast 7.7.7.255
up ip route add 7.7.7.0/24 dev eth0 src 7.7.7.4 table eth0table
up ip route add default via 7.7.7.1 dev eth0 table eth0table
up ip rule add from 7.7.7.4 table eth0table
up ip route add 7.7.7.0/24 dev eth0 src 7.7.7.4
auto eth1
iface eth1 inet static
address 7.7.7.5
network 7.7.7.0
netmask 255.255.255.0
broadcast 7.7.7.255
up ip route add 7.7.7.0/24 dev eth1 src 7.7.7.5 table eth1table
up ip route add default via 7.7.7.1 dev eth1 table eth1table
up ip rule add from 7.7.7.5 table eth1table
up ip route add default via 7.7.7.1 dev eth1
up ip route add 7.7.7.0/24 dev eth1 src 7.7.7.5 Add the following two lines to /etc/iproute2/rt_tables
10 eth0table
20 eth1table The following is also relevant:
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.4.2.1. Split access
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 $IF1 be the name of the
first interface (if1 in the picture above) and $IF2 the name of the
second interface. Then let $IP1 be the IP address associated with
$IF1 and $IP2 the IP address associated with
$IF2. Next, let $P1 be the IP address of the gateway at
Provider 1, and $P2 the IP address of the gateway at provider 2.
Finally, let $P1_NET be the IP network $P1 is in,
and $P2_NET the IP network $P2 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 $P1_NET dev $IF1 src $IP1 table T1 ip route add default via $P1 table T1 ip route add $P2_NET dev $IF2 src $IP2 table T2 ip route add default via $P2 table T2
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 $P1_NET dev $IF1 src $IP1
ip route add $P2_NET dev $IF2 src $IP2
Then, your preference for default route:ip route add default via $P1
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.
notes: 'If $P0_NET is the local network and $IF0 is its interface,
the following additional entries are desirable:
ip route add $P0_NET dev $IF0 table T1 ip route add $P2_NET dev $IF2 table T1 ip route add 127.0.0.0/8 dev lo table T1 ip route add $P0_NET dev $IF0 table T2 ip route add $P1_NET dev $IF1 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.
4.2.2. Load balancing
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 $P1 dev $IF1 weight 1 \
nexthop via $P2 dev $IF2 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.
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