How to Display Current TCP Traffic on a Cisco Router

Written by jonah quant
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How to Display Current TCP Traffic on a Cisco Router
You can instruct a Cisco router to list all open TCP connections. (Hemera Technologies/ Images)

Cisco network routers forward incoming packets via the output port that gets them closest to their ultimate destination. At any given time, a router may be forwarding packets for many established TCP (Transmission Control Protocol) connections. Since the router must keep track of all current connections, you can access its administrative interface and list all TCP connections in progress at any given time.

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  1. 1

    Launch the router's administrative interface. The specific way of performing this operation depends on the make and model of the router. For example, for Cisco routers running IOS, launch the terminal emulator application on the computer. The router will present you with a login prompt via the console interface.

  2. 2

    Log in to the router with administrator privileges. For example, for IOS routers,

    type "en" and press "Enter." Enter the router's administrator password, then press "Enter."

  3. 3

    Display the current connection table for the router. For example, for IOS routers, type

    show control-plane host open-ports

    Press "Enter." The router will display a table with one line for each currently open connection. The fourth column from the left is labelled "Service;" the entries under that column correspond to the protocols currently in use. The current TCP traffic corresponds exactly to the table entries that have "TCP" under the fourth column.

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