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# SSH

SSH (Secure Shell) was developed in 1995 ti replace less secure protocols like Telnet.

SSHv2, a major revisiion of SSHv1, was released in 2006.

If a device supports both version 1 and version2, it is said to run 'version 1.99'.

Provides security features such as data encryption and authentication.

<figure><img src="/files/uTlI8mi8X7Qjtwj0SIvV" alt=""><figcaption></figcaption></figure>

The SSH *server* (the device being connected to) listens for SSH traffic on **TCP port 22**.

## Configuration

<figure><img src="/files/G8mowDd8R2byrmuO4S7b" alt=""><figcaption></figcaption></figure>

IOS images that support SSH will have '**K9**' in their name.

Cisco exports NPE (No Payload Encryption) IOS images to countries that have restrictions on encryption technologies.

NPE IOS images do not support cryptographic features such as SSH.

### RSA keys

To enable and use SSH, you must generate an RSA public and private key pair.

The keys are used for daa encryption/decryption, authentication, etc.

* `ip domain name jeremysitlab.com` -> the **FQDN** of the device is used to name the RSA keys. FQDN = Fully Qualified Domain Name (host name + domain name).
* `crypto key generate rsa` -> generates the RSA keys.
  * `crypto key generate rsa modulus <length>` is and alternate method. Length must be 768 bits or greater for SHHv2.

### VTY Lines

1. `ip ssh version 2` -> (optional, but recommended) restrict SSH to version 2 only.
2. `line vty 0 15` -> configure all VTY lines, just like Telnet.
3. `login local` -> enable local user authentication. You cannot use `login` for SSH, only `login local`.
4. `exec-timeout 5 0` -> (optional, but recommended) configure the exec timeout.
5. `transport input ssh` -> best practice is to limit VTY line connections to SSH only.
6. `access-class 1 in` -> (optional, but recommended) apply the ACL to restrict VTY line connections.


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