Transit Gateway

AWS Transit Gateway connects VPCs and on-premises networks through a central hub. This simplifies your network and puts an end to complex peering relationships. It acts as a cloud router - each new connection is only made once.

Key facts:

• Allows to have transitive peering between thousands of VPCs and on-premises data centers.

• Works on a hub-and-spoke model.

• Works on a regional basis, but you can have it across multiple regions.

• You can use it across multiple AWS accounts using RAM (Resource Access Manager).

• You can use route tables to limit how VPCs talk to one another.

• Works with Direct Connect as well as VPN connections.

• Support IP multicast (not supported by any other AWS service)

IP Multicast

IP multicast support means a network device or system can handle multicast communication protocols, where data is transmitted from one sender to multiple receivers simultaneously.

Here's what this involves:

Basic concept: Instead of sending separate copies of data to each recipient (unicast) or broadcasting to everyone on a network (broadcast), multicast sends one copy that gets replicated only where needed along the network path.

Key technical aspects:

• Multicast addressing: Uses special IP address ranges (224.0.0.0 to 239.255.255.255 for IPv4)

• Group management: Devices can join or leave multicast groups using protocols like IGMP (Internet Group Management Protocol)

• Efficient routing: Routers create distribution trees to deliver data only to network segments with interested receivers

• Protocol support: Handles multicast-specific protocols and packet forwarding rules

Common applications:

• Video streaming and live broadcasts

• Software updates distributed to multiple computers

• Real-time financial data feeds

• Online gaming with multiple players

• Video conferencing

Why it matters: Multicast is much more bandwidth-efficient than sending individual streams to each recipient. For example, streaming video to 1000 users requires only one stream from the source rather than 1000 separate streams.

When a device lists "IP multicast support," it means it can participate in these multicast communications either as a sender, receiver, or intermediate router that properly forwards multicast traffic.