# CreateTrafficMirrorSession
Creates a Traffic Mirror session.
A Traffic Mirror session actively copies packets from a Traffic Mirror source to a Traffic Mirror target. Create a filter, and then assign it to the session to define a subset of the traffic to mirror, for example all TCP traffic.
The Traffic Mirror source and the Traffic Mirror target (monitoring appliances) can be in the same VPC, or in a different VPC connected via VPC peering or a transit gateway.
By default, no traffic is mirrored. Use [CreateTrafficMirrorFilter](https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_CreateTrafficMirrorFilter.html) to create filter rules that specify the traffic to mirror.
## Request Parameters
The following parameters are for this specific action. For more information about required and optional parameters that are common to all actions, see [Common Query Parameters](CommonParameters.md).
**ClientToken**
Unique, case-sensitive identifier that you provide to ensure the idempotency of the request. For more information, see [How to ensure idempotency](https://docs.aws.amazon.com/ec2/latest/devguide/ec2-api-idempotency.html).
Type: String
Required: No
**Description**
The description of the Traffic Mirror session.
Type: String
Required: No
**DryRun**
Checks whether you have the required permissions for the action, without actually making the request, and provides an error response. If you have the required permissions, the error response is `DryRunOperation`. Otherwise, it is `UnauthorizedOperation`.
Type: Boolean
Required: No
**NetworkInterfaceId**
The ID of the source network interface.
Type: String
Required: Yes
**PacketLength**
The number of bytes in each packet to mirror. These are bytes after the VXLAN header. Do not specify this parameter when you want to mirror the entire packet. To mirror a subset of the packet, set this to the length (in bytes) that you want to mirror. For example, if you set this value to 100, then the first 100 bytes that meet the filter criteria are copied to the target.
If you do not want to mirror the entire packet, use the `PacketLength` parameter to specify the number of bytes in each packet to mirror.
For sessions with Network Load Balancer (NLB) Traffic Mirror targets the default `PacketLength` will be set to 8500. Valid values are 1-8500. Setting a `PacketLength` greater than 8500 will result in an error response.
Type: Integer
Required: No
**SessionNumber**
The session number determines the order in which sessions are evaluated when an interface is used by multiple sessions. The first session with a matching filter is the one that mirrors the packets.
Valid values are 1-32766.
Type: Integer
Required: Yes
**TagSpecification.N**
The tags to assign to a Traffic Mirror session.
Type: Array of [TagSpecification](API_TagSpecification.md) objects
Required: No
**TrafficMirrorFilterId**
The ID of the Traffic Mirror filter.
Type: String
Required: Yes
**TrafficMirrorTargetId**
The ID of the Traffic Mirror target.
Type: String
Required: Yes
**VirtualNetworkId**
The VXLAN ID for the Traffic Mirror session. For more information about the VXLAN protocol, see [RFC 7348](https://datatracker.ietf.org/doc/html/rfc7348). If you do not specify a `VirtualNetworkId`, an account-wide unique ID is chosen at random.
Type: Integer
Required: No
## Response Elements
The following elements are returned by the service.
**clientToken**
Unique, case-sensitive identifier that you provide to ensure the idempotency of the request. For more information, see [How to ensure idempotency](https://docs.aws.amazon.com/ec2/latest/devguide/ec2-api-idempotency.html).
Type: String
**requestId**
The ID of the request.
Type: String
**trafficMirrorSession**
Information about the Traffic Mirror session.
Type: [TrafficMirrorSession](API_TrafficMirrorSession.md) object
## Errors
For information about the errors that are common to all actions, see [Common client error codes](errors-overview.md#CommonErrors).
## See Also
For more information about using this API in one of the language-specific AWS SDKs, see the following:
+ [AWS Command Line Interface V2](https://docs.aws.amazon.com/goto/cli2/ec2-2016-11-15/CreateTrafficMirrorSession)
+ [AWS SDK for .NET V4](https://docs.aws.amazon.com/goto/DotNetSDKV4/ec2-2016-11-15/CreateTrafficMirrorSession)
+ [AWS SDK for C\$1\$1](https://docs.aws.amazon.com/goto/SdkForCpp/ec2-2016-11-15/CreateTrafficMirrorSession)
+ [AWS SDK for Go v2](https://docs.aws.amazon.com/goto/SdkForGoV2/ec2-2016-11-15/CreateTrafficMirrorSession)
+ [AWS SDK for Java V2](https://docs.aws.amazon.com/goto/SdkForJavaV2/ec2-2016-11-15/CreateTrafficMirrorSession)
+ [AWS SDK for JavaScript V3](https://docs.aws.amazon.com/goto/SdkForJavaScriptV3/ec2-2016-11-15/CreateTrafficMirrorSession)
+ [AWS SDK for Kotlin](https://docs.aws.amazon.com/goto/SdkForKotlin/ec2-2016-11-15/CreateTrafficMirrorSession)
+ [AWS SDK for PHP V3](https://docs.aws.amazon.com/goto/SdkForPHPV3/ec2-2016-11-15/CreateTrafficMirrorSession)
+ [AWS SDK for Python](https://docs.aws.amazon.com/goto/boto3/ec2-2016-11-15/CreateTrafficMirrorSession)
+ [AWS SDK for Ruby V3](https://docs.aws.amazon.com/goto/SdkForRubyV3/ec2-2016-11-15/CreateTrafficMirrorSession)