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Bit of a newb question but just curious if it can be done.

Is it possible to have multiple hosts with the same ip/subnet (eg 10.101.30.10/24) each seperated by a layer 3 switch/router, where one of the hosts could be streaming a multicast rtp stream to all the other hosts??

Cheers,

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You cannot have the same IP network on different layer 3 interfaces of the same gateway device (router or layer 3 switch, firewall, etc.) without the use of a feature like VRF to logically segment the networks from each other into separate forwarding tables.

You can have different IP networks on different layer 3 interfaces of the same gateway device and use NAT to make them appear to act as the same IP network to a degree.

If the networks in question are connected via different gateway devices then you can have the same IP network on the two networks but for them to communicate directly you need a combination of features to make each network appear as a connected network or as a different network (VXLAN, VPN, Tunneling of some kind, etc.).

If you meant hosts in the same single network separated by a basic layer 3 gateway, then no, once you have a layer 3 gateway in between devices, it is no longer a contiguous network (unless you have other special features again to make it work as a single network).

If you simply mean 'does multicast work over routers?' then yes, multicast routing is a feature available on many business class routers.

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Using unicast with duplicate/ambiguous addresses requires some form of NAT/NAPT between the subnets. Basically, you use a gateway to translate each subnet to an unambiguous prefix an egress and map that prefix to the duplicate address on ingress.

This setup isn't possible with a (simple) layer-3 switch. Using a single NAPT router between duplicate subnets requires it to use VRF instances and translate between them.

Multicast between subnets additionally requires multicast routing like PIM which isn't usually available in a layer-3 switch either.

As it is, you'd need to select a router with the required features (VRF with NAPT in between, PIM). Renumbering the subnets to enable unambiguous addressing would solve the translation problem (which is very heavy lifting for a newbie) and you'd just need a PIM router.

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