# ModifyTransitGatewayOptions
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The transit gateway options.

## Contents
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 ** AddTransitGatewayCidrBlocks.N **   
Adds IPv4 or IPv6 CIDR blocks for the transit gateway. Must be a size /24 CIDR block or larger for IPv4, or a size /64 CIDR block or larger for IPv6.  
Type: Array of strings  
Required: No

 ** AmazonSideAsn **   
A private Autonomous System Number (ASN) for the Amazon side of a BGP session. The range is 64512 to 65534 for 16-bit ASNs and 4200000000 to 4294967294 for 32-bit ASNs.  
The modify ASN operation is not allowed on a transit gateway if it has the following attachments:  
+ Dynamic VPN
+ Static VPN
+ Direct Connect Gateway
+ Connect
You must first delete all transit gateway attachments configured prior to modifying the ASN on the transit gateway.  
Type: Long  
Required: No

 ** AssociationDefaultRouteTableId **   
The ID of the default association route table.  
Type: String  
Required: No

 ** AutoAcceptSharedAttachments **   
Enable or disable automatic acceptance of attachment requests.  
Type: String  
Valid Values: `enable | disable`   
Required: No

 ** DefaultRouteTableAssociation **   
Enable or disable automatic association with the default association route table.  
Type: String  
Valid Values: `enable | disable`   
Required: No

 ** DefaultRouteTablePropagation **   
Indicates whether resource attachments automatically propagate routes to the default propagation route table. Enabled by default. If `defaultRouteTablePropagation` is set to `enable`, AWS Transit Gateway will create the default transit gateway route table.  
Type: String  
Valid Values: `enable | disable`   
Required: No

 ** DnsSupport **   
Enable or disable DNS support.  
Type: String  
Valid Values: `enable | disable`   
Required: No

 ** EncryptionSupport **   
Enable or disable encryption support for VPC Encryption Control.  
Type: String  
Valid Values: `enable | disable`   
Required: No

 ** PropagationDefaultRouteTableId **   
The ID of the default propagation route table.  
Type: String  
Required: No

 ** RemoveTransitGatewayCidrBlocks.N **   
Removes CIDR blocks for the transit gateway.  
Type: Array of strings  
Required: No

 ** SecurityGroupReferencingSupport **   
Enables you to reference a security group across VPCs attached to a transit gateway to simplify security group management.   
This option is disabled by default.  
For more information about security group referencing, see [Security group referencing](https://docs.aws.amazon.com/vpc/latest/tgw/tgw-vpc-attachments.html#vpc-attachment-security) in the * AWS Transit Gateways Guide*.  
Type: String  
Valid Values: `enable | disable`   
Required: No

 ** VpnEcmpSupport **   
Enable or disable Equal Cost Multipath Protocol support.  
Type: String  
Valid Values: `enable | disable`   
Required: No

## See Also
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For more information about using this API in one of the language-specific AWS SDKs, see the following:
+  [AWS SDK for C\$1\$1](https://docs.aws.amazon.com/goto/SdkForCpp/ec2-2016-11-15/ModifyTransitGatewayOptions) 
+  [AWS SDK for Java V2](https://docs.aws.amazon.com/goto/SdkForJavaV2/ec2-2016-11-15/ModifyTransitGatewayOptions) 
+  [AWS SDK for Ruby V3](https://docs.aws.amazon.com/goto/SdkForRubyV3/ec2-2016-11-15/ModifyTransitGatewayOptions)