How File Transfers between SFTP Clients and Servers Work

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Our customers have different needs and use cases, but they all appreciate the flexibility of Thru’s client/server functionality. This blog post will describe an SFTP file transfer and explain how we help you meet your file transfer use cases.

Before diving into how the transfer works, it is important to understand the differences between a server and a client.

Server Client
Higher processing power Lower processing power
Has resources shared by every user on the network Used by individual users on the network
Stores information and fulfills requests from client Requests information from server
Passive – never initiates requests Active – always initiates requests
Examples: database server, file server Examples: PCs and laptops

Together, the server and client make up a request-response messaging pattern, in which one party requests the data and the other responds. The term “direction of connection” describes which computer initiates the connection.

How a File Transfer Between an STFP Client and an SFTP Server Works

In this example, the direction of connection is from an SFTP client to an SFTP server. This is how the transfer works:

  1. The server listens for connections on a specific port, typically the TCP (transmission control protocol) port 22. Steps 2-4 describe how the TCP handshake establishes the connection.
  2. The client sends a message (called a SYN) to the server to check its presence.
  3. The server sends an acknowledgement, called a SYN ACK, to the client.
  4. The client sends another acknowledgement message to the server.
  5. After the TCP handshake, the client provides credentials to authenticate the user and server.
  6. The file is transferred and available for download. Users might be able to see additional transfer information, including time/date, size, permissions, etc.

Thru’s Client/Server Functionality

Thru can act as a client or a server to help you meet two types of requirements:

  • Business requirements

    If you and your partner only use servers to transfer files, Thru makes the connection possible.

  • Security requirements

    If a partner prohibits inbound connections for security reasons, they can use a client behind their firewall to push files to Thru, which acts as a server.

Use Cases

With Thru, you can transfer files in any server-client combination:

1. Source Server Endpoint to Target Server Endpoint

Thru pulls files from a source server endpoint and pushes them to a target server endpoint.

transfer files from source server endpoint to target server endpoint


2. Source Client Endpoint to Target Client Endpoint

Note: In Thru, client endpoints require a FTPS/SFTP client application to authenticate, upload and download files.

The source client endpoint pushes files to Thru, then the target client endpoint pulls them.

transfer files from source client endpoint to target client endpoint


3. Source Server Endpoint to Target Client Endpoint

Thru pulls files from a source server endpoint. Then, the target client endpoint pulls files from Thru.

transfer files from source server endpoint to target client endpoint


4. Source Client Endpoint to Target Server Endpoint

The source client endpoint pushes files to Thru, which pushes them to a target server endpoint.

transfer files from source client endpoint to target server endpoint


Client-Server Relationship

Organizations are sometimes limited by the client-server relationship. Because client-to-client and server-to-server file transfers are not possible without an entity in between, the IT team creates and manages more endpoints.

By having client/server functionality, Thru removes endpoint limits and simplifies partner onboarding. In addition to integrating with clients and servers, Thru integrates with integration platforms, productivity apps and more. Learn more about our file transfer integrations.

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