====== Multicast Route ======
<color #db5f0b>Oct 2017</color>
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Multicast routes are a similar concept to IP Routes, but as the name implies they are for Multicast addresses (which are class D), rather than standard IP Addresses (which are class A, B and C). For Unicast I would surmise you still use IP Routes.
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There are two main ways to add a Multicast Route.
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    1. Create a routing file in (CentOS) /etc/sysconfig/network-scripts/
    2. Add the route from the command line.
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===== 1. Create a routing file =====
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In this example, we will define that all multicast traffic in the range 239.X.Y.Z will be listened on the eth2 interface. 
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To do this, navigate to the location where all the interface configuration files are held. On CentOS this is /etc/sysconfig/network-scripts
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    cd /etc/sysconfig/network-scripts
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Create a <color #ed1c24>route config file</color> for your interface (eth2 in this example).
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    vi /etc/sysconfig/network-scripts/route-eth2
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Note, the filename is the word "route" + "-" + "interface name". So if your interface name was eno33559296, then your route file would be called route-eno33559296.
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Now add your routing parameters.
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<file>
GATEWAY0=11.0.100.1
NETMASK0=255.0.0.0
ADDRESS0=239.0.0.0
</file>
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The above routing information routes all traffic that has a multicast address of 239.x.x.x and a subnet of 255.0.0.0 to interface eth2 (as dictated by the name of the file "route-eth2".
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This will route all multicast traffic requests on 239.X.Y.Z scope to interface Eth2, which has the IP address 11.0.100.1. The 'Gateway' in this instance is an interface address. 
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Save and close the file. Restart networking or restart the server.
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===== 2. Add the route from the command line =====
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We can add the route from the command line, this does not create a file for us in the /etc/sysconfig/network-scripts folder, I don't actually know where it gets stored (or if it is persistent). so you need to test this method.
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In this example we are going to add a multicast route 224.0.0.0/4 (/4 = 240.0.0.0) to an interface called eno33559296. 224.0.0.0/4 basically means everything from 239.0.0.0 to 224.255.255.255, so all multicast addresses.
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From the command line, enter the following:
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    ip route add 224.0.0.0/4 dev eno33559296
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You can check to see if the route has taken by using the following:
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    ip route
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you will see a table of routes, with the new route added.
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<file>
Destination     Gateway         Genmask         Flags Metric Ref    Use IfaceD
default         10.43.0.3       0.0.0.0         UG    100    0        0 eno16780032
10.0.0.0        10.0.3.70       255.0.0.0       UG    0      0        0 eno33559296
10.0.3.0        0.0.0.0         255.255.255.0   U     100    0        0 eno33559296
10.43.0.0       0.0.0.0         255.255.224.0   U     100    0        0 eno16780032
224.0.0.0       0.0.0.0         240.0.0.0       U     0      0        0 eno33559296
</file>
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The last line <color #ed1c24>224.0.0.0 - 0.0.0.0 - 240.0.0.0 - U - 0 - 0 - 0 - eno33559296</color> is our new route.
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