System Security Configuration Guide for Cisco 8000 Series Routers, IOS XR Releases

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System Security Configuration Guide for Cisco 8000 Series Routers, IOS XR Releases

SSH multichannel connections

Updated: September 18, 2026

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Explains how SSH multiplexing carries concurrent shell, remote-command, and secure file-transfer channels through one authenticated TCP connection between a client and server.

An SSH multichannel connection is a multiplexed session that

  • carries multiple SSH channels through one TCP socket

  • authenticates the user once for all channels in the session, and

  • supports simultaneous terminal, command-execution, and file-transfer operations.

Server-side multiplexing is enabled by default. A compatible client must explicitly enable multiplexing.

Benefits of SSH multiplexing

  • Reduces repeated authentication.

  • Avoids establishing a separate TCP connection for each operation.

How SSH multichannel connections work

The client and server use a single authenticated session for multiple concurrent services.

Summary

The process uses these components:

  • Primary connection: Owns the TCP socket and authenticated session.

  • Client channels: Carry independent shell, command, or file-transfer operations.

  • SSH server: Processes each request to open a channel.

Workflow

Figure 1. Client-server interaction over a SSH multichannel connection

These stages describe SSH multiplexing:

  1. The client creates a primary SSH connection and authenticates the user.

  2. A later client operation locates the existing control socket instead of creating another TCP connection.

  3. The client requests a new channel for the operation. The server processes that request as one service.

  4. The client multiplexes traffic from all active channels through the primary connection.

Result

Multiple operations share one authenticated TCP connection while their SSH channels remain logically independent.

SSH multichannel connection restrictions

Review these limits before enabling client multiplexing.

SSH multiplexing has these restrictions:

  • Do not use one multiplexed connection for heavy data transfer because all channels share that connection's TCP speed limit.

  • Do not use more than 15 concurrent channels in one session.

  • Cisco IOS XR software provides server-side multiplexing; the client must provide compatible client-side support.