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# AWS::EC2::TransitGatewayMulticastGroupSource

Registers sources (network interfaces) with the specified transit gateway multicast domain.
A multicast source is a network interface attached to a supported instance that sends multicast traffic. For information about supported instances, see [Multicast Considerations](https://docs.aws.amazon.com/vpc/latest/tgw/transit-gateway-limits.html#multicast-limits) in *Amazon VPC Transit Gateways*.
## Syntax

To declare this entity in your CloudFormation template, use the following syntax:
### JSON

```
{
 "Type" : "AWS::EC2::TransitGatewayMulticastGroupSource",
 "Properties" : {
 "[GroupIpAddress](#cfn-ec2-transitgatewaymulticastgroupsource-groupipaddress)" : {{String}},
 "[NetworkInterfaceId](#cfn-ec2-transitgatewaymulticastgroupsource-networkinterfaceid)" : {{String}},
 "[TransitGatewayMulticastDomainId](#cfn-ec2-transitgatewaymulticastgroupsource-transitgatewaymulticastdomainid)" : {{String}}
 }
}
```
### YAML

```
Type: AWS::EC2::TransitGatewayMulticastGroupSource
Properties:
 [GroupIpAddress](#cfn-ec2-transitgatewaymulticastgroupsource-groupipaddress): {{String}}
 [NetworkInterfaceId](#cfn-ec2-transitgatewaymulticastgroupsource-networkinterfaceid): {{String}}
 [TransitGatewayMulticastDomainId](#cfn-ec2-transitgatewaymulticastgroupsource-transitgatewaymulticastdomainid): {{String}}
```
## Properties

`GroupIpAddress` 
The IP address assigned to the transit gateway multicast group. 
*Required*: Yes 
*Type*: String 
*Update requires*: [Replacement](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/using-cfn-updating-stacks-update-behaviors.html#update-replacement)
`NetworkInterfaceId` 
The group sources' network interface IDs to register with the transit gateway multicast group. 
*Required*: Yes 
*Type*: String 
*Update requires*: [Replacement](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/using-cfn-updating-stacks-update-behaviors.html#update-replacement)
`TransitGatewayMulticastDomainId` 
The ID of the transit gateway multicast domain. 
*Required*: Yes 
*Type*: String 
*Update requires*: [Replacement](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/using-cfn-updating-stacks-update-behaviors.html#update-replacement)
## Return values

### Ref

When you pass the logical ID of this resource to the intrinsic `Ref` function, `Ref` returns the transit gateway multicast domain group source. 
### Fn::GetAtt

The `Fn::GetAtt` intrinsic function returns a value for a specified attribute of this type. The following are the available attributes and sample return values.
For more information about using the `Fn::GetAtt` intrinsic function, see [https://docs.aws.amazon.com/AWSCloudFormation/latest/TemplateReference/intrinsic-function-reference-getatt.html](https://docs.aws.amazon.com/AWSCloudFormation/latest/TemplateReference/intrinsic-function-reference-getatt.html).
#### 

`GroupMember` 
Information about the registered transit gateway multicast domain group members.
`GroupSource` 
Indicates that the resource is a transit gateway group member.
`ResourceId` 
The ID of the resource.
`ResourceType` 
The type of resource, for example a VPC attachment.
`SourceType` 
The type of source.
`SubnetId` 
The ID of the subnet.
`TransitGatewayAttachmentId` 
The ID of the transit gateway attachment.
## See also

+ [RegisterTransitGatewayMulticastGroupSources](https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_RegisterTransitGatewayMulticastGroupSources.html) in the *Amazon EC2 API Reference*
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