84. How to deny Telnet with the help of ACL | Deny Telnet using extended ACL | 200-301 | Part - 5
To deny Telnet traffic using an Access Control List (ACL), you can create and apply the ACL on your networking equipment, such as a router or a firewall. Telnet uses TCP port 23 by default, so you'll need to deny traffic to this port in your ACL. Here's a step-by-step guide on how to do it:
Access your networking equipment:
Connect to the device via SSH, console cable, or any other method appropriate for your device.
Enter privileged exec mode:
Type enable and enter the enable password if prompted. This will give you elevated privileges to make configuration changes.
Create an Access Control List (ACL):
Use the following commands to create an ACL. This example uses a numbered standard ACL, but you can adapt it for extended ACLs if needed.
arduino
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configure terminal
access-list 100 deny tcp any any eq 23
access-list 100 permit ip any any
configure terminal
access-list 100 deny tcp any any eq 23
access-list 100 permit ip any any
In this example, we:
Created ACL number 100.
Denied any TCP traffic from any source to any destination on port 23 (Telnet).
Allowed all other IP traffic.
Apply the ACL to an interface:
Now, apply the ACL to the interface that you want to deny Telnet traffic on. Replace interface_name with the actual name of the interface.
kotlin
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interface interface_name
ip access-group 100 in
This command applies the ACL inbound on the specified interface.
Save the configuration:
Save the configuration changes to ensure they persist after a device reboot or power cycle.
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write memory
Verify the configuration:
You can verify that the ACL is applied correctly by using the following command:
sql
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show access-list
This command will display the configured ACLs, and you should see your ACL (number 100) listed with the rules you defined.
By following these steps, you've effectively denied Telnet traffic to your network by blocking it at the specified interface. Make sure that your ACL configuration doesn't interfere with other legitimate network traffic and that you've properly tested it in your environment before applying it in a production setting.
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