In continuation of my previous posts where i’m create a distributed cloud infrastructure i need to connect VM’s on multiple Host Machines
Pre knowledge of routing (IPTables) and networking is required for information below. Technically this is what containers like docker or software routers do internally when they need to connect 2 different network’s
Lets assume
HostMachine1 has VM’s on network 10.0.0.1/24
HostMachine2 has VM’s on network 192.168.0.1/24
Now our Gateway1 and Gateway2 have 2 Network Interfaces/NIC cards.
Gateway1 and Gateway2 are connected by switch hence on same network as well as their respective VM networks as they have 2 NIC cards connected.
Let assume Gateway1 has IP 10.0.0.2
Let assume Gateway2 has IP 192.168.0.2
Both Gateway1 and Gateway2 can connect to each other as they are directly connected.
My Current Configuration on Gateway1 which is our target router and i’ve below Network Interfaces on that
enp0s9: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 08:00:27:9d:08:3f brd ff:ff:ff:ff:ff:ff
inet 10.0.0.169/24 brd 10.0.0.255 scope global enp0s9
valid_lft forever preferred_lft forever
inet6 fe80::a00:27ff:fe9d:83f/64 scope link
valid_lft forever preferred_lft forever
enp0s10: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 08:00:27:7b:12:89 brd ff:ff:ff:ff:ff:ff
inet 192.168.1.120/16 brd 192.168.255.255 scope global enp0s10
valid_lft forever preferred_lft forever
inet6 fe80::a00:27ff:fe7b:1289/64 scope link
Now we need to add routing table configurations on either gateway1 or gateway2 to forward packets from one network to another.
We can do this 2 ways.
Either by creating network bridge
# Install brige utils that gives us easy commands to creatr bridge network apt-get install bridge-utils or yum install bridge-utils # Create new Bridge brctl addbr br0 # Enable Spanning Tree Support if you need brctl stp br0 on # Make sure you get your Devices down before creating bridge and explicity assign 0.0.0.0 to make sure they loose ip ifconfig enp0s9 0.0.0.0 down ifconfig enp0s10 0.0.0.0 down # Add them to our newly created bridge network brctl addif br0 enp0s9 brctl addif br0 enp0s10 # Finally get all interfaces up. ifconfig enp0s9 up ifconfig enp0s10 up ifconfig br0 up
or
by modifying routing table. I’m explaining second concept here
Enable forwarding in the kernel:
echo 1 >> /proc/sys/net/ipv4/ip_forward
To set this value on boot uncomment this line in/etc/sysctl.conf
#net.ipv4.ip_forward=1
Now i need to route traffic from one Interface to another using routing tables
Below are statements that can do that
# Always accept loopback traffic iptables -A INPUT -i lo -j ACCEPT # We allow traffic from the HostMachine1 side iptables -A INPUT -i enp0s9 -j ACCEPT # We allow traffic from the HostMachine2 side iptables -A INPUT -i enp0s10 -j ACCEPT ###################################################################### # # ROUTING # ###################################################################### # enp0s9 is HostMachine1 Network # enp0s10 is HostMachine2 Network # Allow established connections iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT # Masquerade. iptables -t nat -A POSTROUTING -o enp0s10 -j MASQUERADE # fowarding iptables -A FORWARD -i enp0s9 -o enp0s10 -m state --state RELATED,ESTABLISHED -j ACCEPT # Allow outgoing connections from the HostMachine1 side. iptables -A FORWARD -i enp0s10 -o enp0s9 -j ACCEPT
Finally on HostMachine1 route all traffic on subnet 192.168.0.1/24 to Gateway1
I use Mac as one my host machine hence below command
sudo route -n add 192.168.1.1/24 10.0.0.169
If you are using any *nix systems command would be
ip route add 192.168.1.1/24 via 10.0.0.169 dev
| Reference: | Linux Box as Router from our SCG partner Ashwin Kumar at the Technology Portal blog. |
