Multicast routing with PIM-SM over GRE

GRE tunnels are useful in many ways. This blog post shows how to set up multicast routing with pimd over a GRE tunnel. To achieve this we will also set up OSPF over GRE with Quagga, because PIM, unlike DVMRP (mrouted), require unicast routing rules to be established.

       .----{ Intranet }----.
      /    192.168.1.0/24    \
     /                        \
.10 /                          \.20
.--'---. .1  GRE Tunnel  .2 .---`--.
|      |====================|      |
|  R1  |   172.16.16.0/30   |  R2  |
|      |                    |      |
'--.---'                    '------'
   | .1                        | .1 
   |    10.0.1.0/24            |    10.0.2.0/24
   | .2                        | .2 
.--'---.                    .--'---.
|      |                    |      |
|  C1  |                    |  C2  |
|      |                    |      |
'------'                    '------'

In this post we are using the home WiFi network, 192.168.1.0/24, to hook up the GRE tunnel. It is just as easy to extend this to a big corporate Intranet with more routers between R1 and R2. As long as that IT department takes care of the unicast routing between R1 and R2 so that the GRE tunnel can be established.

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