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This chapter contains the following sections:
Information About SSH
You can use the Secure Shell (SSH) server to enable an SSH client to make a secure, encrypted connection. SSH uses strong encryption for authentication. The SSH server can operate with publicly and commercially available SSH clients.
TACACS+ user authentication and locally stored usernames and passwords are supported for SSH.
The SSH client feature is an application that runs over the SSH protocol to provide device authentication and encryption. The SSH client enables a secure, encrypted connection to any device that runs the SSH server. This connection provides an encrypted outbound connection. With authentication and encryption, the SSH client produces secure communication over an insecure network.
The SSH client works with publicly and commercially available SSH servers.
SSH requires server keys for secure communication. You can use SSH server keys for the following SSH options:
SSH version 2 using Rivest, Shamir, and Adelman (RSA) public-key cryptography
SSH version 2 using the Digital System Algrorithm (DSA)
Be sure to have an SSH server key-pair with the correct version before enabling the SSH service. Generate the SSH server key-pair according to the SSH client version used. The SSH service accepts two types of key-pairs for use by SSH version 2:
The dsa option generates the DSA key-pair for the SSH version 2 protocol.
The rsa option generates the RSA key-pair for the SSH version 2 protocol.
By default, an RSA key that uses 1024 bits is generated.
SSH supports the following public key formats
OpenSSH
IETF Secure Shell (SECSH)
Public Key Certificate in Privacy-Enhanced Mail (PEM)
 Caution |
If you delete all of the SSH keys, you cannot start the SSH services. |
Configure IP on a Layer 3 interface, out-of-band on the mgmt 0 interface or inband on an Ethernet interface. SSH supports both IPv4 and IPv6 addresses.
Before enabling the SSH server, obtain the SSH key.
Only SSH version 2 (SSHv2) is supported.
SSH is enabled by default.
Cisco NX-OS commands might differ from the Cisco IOS commands.
|
Parameters |
Default |
|---|---|
|
SSH server |
Enabled |
|
SSH server key |
RSA key generated with 1024 bits |
|
RSA key bits for generation |
1024 |
Configuring SSH
You can generate an SSH server key based on your security requirements.
The default SSH server key is an RSA key that is generated using 1024 bits.
Log in to the CLI in EXEC mode.
| Command or Action | Purpose | |
|---|---|---|
| Step 1 |
switch# configure terminal |
Enters global configuration mode. |
| Step 2 |
switch(config)# no feature ssh |
Disables SSH. |
| Step 3 |
switch(config)# ssh key {dsa [force ] | rsa [bits[ force ]]} |
Generates the SSH server key The bits argument is the number of bits used to generate the key. The range is from 768 to 2048 and the default value is 1024. Use the force keyword to replace an existing key. |
| Step 4 |
switch(config)# feature ssh |
Enables SSH. |
| Step 5 |
(Optional) switch# show ssh key |
(Optional)
Displays the SSH server keys. |
| Step 6 |
(Optional) switch# copy running-config startup-config |
(Optional)
Copies the running configuration to the startup configuration. |
This example shows how to generate SSH server keys:
switch# configure terminal
switch(config)# no feature ssh
XML interface to system may become unavailable since ssh is disabled
switch(config)# ssh key dsa force
generating dsa key(1024 bits).....
.
generated dsa key
n1000v(config)# feature ssh
n1000v(config)# show ssh key
**************************************
rsa Keys generated:Sun Jul 27 15:18:46 2008
ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAyKcb7Nv9Ki1OOId9/tdHHa/ngQujlvK5mXyL/n+DeOXK
fVhHbX2a+V0cm7CCLUkBh+BvZRmpmOVTmU/5awfVhVxMKXMiPOPBc+A6/n3FVroyRwupMki6mWoM6Uwa
GID5gsVPqFjFNSgMWtbhjo97XVKhgjFW+wOVt8QoAcrEtnwEfsnQk1EIr/0XIP1mqTsrqTsmjZ2vLk+f
FzTGYAxMvYZI+BrN47aoH2ywS7CpnODjCDXJuDYSPbc3PA8t0ghU/60m9R+s6AZPuljVQbGfxPrahEu4
GVc6sMJNU1JxmqDJkodhMArObB4Umzj7E3Rdby/ZWx/clTYiXQR1X1VfhQ==
bitcount:2048
fingerprint:
fd:ca:48:73:b9:ee:e7:86:9e:1e:40:46:f1:50:1d:44
**************************************
dsa Keys generated:Sun Jul 27 15:20:12 2008
ssh-dss AAAAB3NzaC1kc3MAAACBALpdxLjXNS/jcCNY+F1QZV9HegxBEb0DMUmq9bSq2N+KAcvHllEh
GnaiHhqarOlcEKqhLbIbuqtKTCvfa+Y1hBIAhWVjg1UR3/M22jqxnfhnxL5YRc1Q7fcesFax0myayAIU
nXrkO5iwv9XHTu+EInRc4kJ0XrG9SxtLmDe/fi2ZAAAAFQDbRabAjZa6GfDpwjXw5smRhrElJwAAAIEA
r50yi3hHawNnb5qgYLXhN+KA8XJF753eCWHtMw7NR8fz6fjQ1R2J97UjjGuQ8DvwpGeNQ5S+AuIo0rGq
svdg7TTecBcbgBOnR7Fs2+W5HiSVEGbvj1xaeK8fkNE6kaJumBB343b8Rgj0G97MP/os1GfkEqmX9glB
0IOM2mgHHyoAAACAfRir27hHy+fw8CxPlsK0R6cFhxYyd/qYYogXFKYIOPxpLoYrjqODeOFThU7TJuBz
aS97eXiruzbffHwzUGfXgmQT5o9IMZRTClWPA/5Ju4O9YABYHccUghf0W+QtgGOT6FOSvBh8uOV0kcHC
GMJAP8omphauZJlc+wgFxhnkyh4=
bitcount:1024
fingerprint:
44:91:32:1f:7a:d1:83:3c:f3:5e:db:53:0a:2d:ce:69
**************************************
You configure an SSH public key to log in using the SSH client without being prompted for a password. You can specify the SSH public key in one of three different formats:
OpenSSH format
IETF SECSH format
Public Key Certificate in PEM format
You can specify the SSH public keys in OpenSSH format for user accounts.
OpenSSH format
IETF SECSH format
Public Key Certificate in PEM format
Log in to the CLI in EXEC mode
Generate an SSH public key in OpenSSH format
Have an existing user account
| Command or Action | Purpose | |
|---|---|---|
| Step 1 |
switch# configure terminal |
Enters global configuration mode. |
| Step 2 |
switch(config)# username username sshkey ssh-key |
Configures the SSH public key in OpenSSH format with an exiting user account. To create a user account use the username name password pwd command. |
| Step 3 |
switch(config)# exit |
Exits global configuration mode and returns to EXEC mode. |
| Step 4 |
(Optional) switch# show user-account |
(Optional)
Displays the user account configuration. |
| Step 5 |
(Optional) switch# copy running-config startup-config |
(Optional)
Copies the running configuration to the startup configuration. |
This example shows how to configure an openSSH key:
switch# configure terminal
switch(config)# username user1 sshkey ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAyK
cb7Nv9Ki1OOId9/tdHHa/ngQujlvK5mXyL/n+DeOXKfVhHbX2a+V0cm7CCLUkBh+BvZRmpmOVTmU/5aw
fVhVxMKXMiPOPBc+A6/n3FVroyRwupMki6mWoM6UwaGID5gsVPqFjFNSgMWtbhjo97XVKhgjFW+wOVt8
QoAcrEtnwEfsnQk1EIr/0XIP1mqTsrqTsmjZ2vLk+fFzTGYAxMvYZI+BrN47aoH2ywS7CpnODjCDXJuD
YSPbc3PA8t0ghU/60m9R+s6AZPuljVQbGfxPrahEu4GVc6sMJNU1JxmqDJkodhMArObB4Umzj7E3Rdby
/ZWx/clTYiXQR1X1VfhQ==
switch(config)# exit
switch# show user-account
user:admin
this user account has no expiry date
roles:network-admin
user:user1
this user account has no expiry date
roles:network-operator
ssh public key: ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAyKcb7Nv9Ki1OOId9/tdH
Ha/ngQujlvK5mXyL/n+DeOXKfVhHbX2a+V0cm7CCLUkBh+BvZRmpmOVTmU/5awfVhVxMKXMiPOPBc+A6
/n3FVroyRwupMki6mWoM6UwaGID5gsVPqFjFNSgMWtbhjo97XVKhgjFW+wOVt8QoAcrEtnwEfsnQk1EI
r/0XIP1mqTsrqTsmjZ2vLk+fFzTGYAxMvYZI+BrN47aoH2ywS7CpnODjCDXJuDYSPbc3PA8t0ghU/60m
9R+s6AZPuljVQbGfxPrahEu4GVc6sMJNU1JxmqDJkodhMArObB4Umzj7E3Rdby/ZWx/clTYiXQR1X1Vf
hQ==
switch# copy running-config startup-config
You can specify the SSH public keys in IETF SECSH or PEM format for user accounts.
OpenSSH format
IETF SECSH format
Public Key Certificate in PEM format
Log in to the CLI in EXEC mode
Generate an SSH public key in one of the following formats:
IETF SECSH format
Public Key Certificate in PEM format
| Command or Action | Purpose | |
|---|---|---|
| Step 1 |
switch# copy server-file bootflash: filename |
Downloads the file containing the SSH key from a server. The server can be FTP, secure copy (SCP), secure FTP (SFTP), or TFTP. |
| Step 2 |
switch# configure terminal |
Enters global configuration mode. |
| Step 3 |
switch(config)# username username sshkey file bootflash: filename |
Configures the SSH public key. |
| Step 4 |
switch(config)# exit |
Exits global configuration mode and returns to EXEC mode. |
| Step 5 |
(Optional) switch# show user-account |
(Optional)
Displays the user account configuration. |
| Step 6 |
(Optional) switch# copy running-config startup-config |
(Optional)
Copies the running configuration to the startup configuration. |
This example shows how to configure an SSH public key in an IETF SECSH format:
switch# copy tftp://10.78.1.10/secsh_file.pub bootflash:secsh_file.pub vrf management
Trying to connect to tftp server......
Connection to server Established.
|
TFTP get operation was successful
switch# configure terminal
switch(config)# username User1 sshkey file bootflash:secsh_file.pub
switch(config)# exit
switch# show user-account
user:admin
this user account has no expiry date
roles:network-admin
user:user2
this user account has no expiry date
roles:network-operator
ssh public key: ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAyKcb7Nv9Ki1OOId9/tdHHa/
ngQujlvK5mXyL/n+DeOXKfVhHbX2a+V0cm7CCLUkBh+BvZRmpmOVTmU/5awfVhVxMKXMiPOPBc+A6/n3FVroyRwupMki6
mWoM6UwaGID5gsVPqFjFNSgMWtbhjo97XVKhgjFW+wOVt8QoAcrEtnwEfsnQk1EIr/0XIP1mqTsrqTsmjZ2vLk+
fFzTGYAxMvYZI+BrN47aoH2ywS7CpnODjCDXJuDYSPbc3PA8t0ghU/60m9R+s6AZPuljVQbGfxPrahEu4GVc6sMJN
U1JxmqDJkodhMArObB4Umzj7E3Rdby/ZWx/clTYiXQR1X1VfhQ==
switch# copy running-config startup-config
You can start SSH sessions using IP to connect to remote devices.
Log in to the CLI in EXEC mode.
Obtain the hostname and, if needed, the username, for the remote device.
Enable the SSH server on the remote device
| Command or Action | Purpose |
|---|---|
|
switch# ssh [root@ ] {ip address | hostname } [vrf vrf-name] or switch# ssh6 [root@ ] {ip address | hostname } [vrf vrf-name] |
Creates an SSH IPv4 or IPv6 session to a remote device using IP. The default virtual routing and forwarding (VRF) instance is the default VRF. |
This example shows how to start an SSH session:
switch# ssh root@172.28.30.77
root@172.28.30.77's password:
Last login: Sat Jul 26 11:07:23 2008 from 171.70.209.64You can clear from your account the list of trusted SSH servers that were added when you downloaded a file from a server using SCP or SFTP, or when you started an SSH session to a remote host.
| Command or Action | Purpose |
|---|---|
|
switch# clear ssh hosts |
Clears the SSH host sessions. |
You can disable the SSH server to prevent SSH access to the switch. By default, the SSH server is enabled.
If you disable SSH, you must first generate an SSH server key before you can enable it again.
Log in to the CLI in EXEC mode.
| Command or Action | Purpose | |
|---|---|---|
| Step 1 |
switch# configure terminal |
Enters global configuration mode. |
| Step 2 |
switch(config)# no feature ssh |
Disables the SSH server. The default is enabled. |
| Step 3 |
(Optional) switch(config)# show ssh server |
(Optional)
Displays the SSH server configuration. |
| Step 4 |
(Optional) switch(config)# copy running-config startup-config |
(Optional)
Copies the running configuration to the startup configuration. |
This example shows how to disable the SSH server:
switch# configure terminal
switch(config)# no feature ssh
XML interface to system may become unavailable since ssh is disabled
switch(config)# show ssh server
ssh is not enabled
switch(config)# copy running-config startup-config
You can delete SSH server keys after you disable the SSH server.
If you disable SSH, you must first generate an SSH server key before you can enable it again.
Log in to the CLI in EXEC mode.
| Command or Action | Purpose | |
|---|---|---|
| Step 1 |
switch# configure terminal |
Enters global configuration mode. |
| Step 2 |
switch(config)# no feature ssh |
Disables the SSH server. |
| Step 3 |
switch(config)# no ssh key [dsa | rsa ] |
Deletes the SSH server key. The default is to delete all the SSH keys. |
| Step 4 |
(Optional) switch(config)# show ssh key |
(Optional)
Displays the SSH server key configuration. |
| Step 5 |
(Optional) switch(config)# copy running-config startup-config |
(Optional)
Copies the running configuration to the startup configuration. |
This example shows how to delete an SSH server key:
switch# configure terminal
switch(config)# no feature ssh
switch(config)# no ssh key rsa
switch(config)# show ssh key
**************************************
rsa Keys generated:Sun Jul 27 15:18:46 2008
ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAyKcb7Nv9Ki1OOId9/tdHHa/ngQujlvK5mXyL/n+DeOXK
fVhHbX2a+V0cm7CCLUkBh+BvZRmpmOVTmU/5awfVhVxMKXMiPOPBc+A6/n3FVroyRwupMki6mWoM6Uwa
GID5gsVPqFjFNSgMWtbhjo97XVKhgjFW+wOVt8QoAcrEtnwEfsnQk1EIr/0XIP1mqTsrqTsmjZ2vLk+f
FzTGYAxMvYZI+BrN47aoH2ywS7CpnODjCDXJuDYSPbc3PA8t0ghU/60m9R+s6AZPuljVQbGfxPrahEu4
GVc6sMJNU1JxmqDJkodhMArObB4Umzj7E3Rdby/ZWx/clTYiXQR1X1VfhQ==
bitcount:2048
fingerprint:
fd:ca:48:73:b9:ee:e7:86:9e:1e:40:46:f1:50:1d:44
**************************************
dsa Keys generated:Sun Jul 27 15:20:12 2008
ssh-dss AAAAB3NzaC1kc3MAAACBALpdxLjXNS/jcCNY+F1QZV9HegxBEb0DMUmq9bSq2N+KAcvHllEh
GnaiHhqarOlcEKqhLbIbuqtKTCvfa+Y1hBIAhWVjg1UR3/M22jqxnfhnxL5YRc1Q7fcesFax0myayAIU
nXrkO5iwv9XHTu+EInRc4kJ0XrG9SxtLmDe/fi2ZAAAAFQDbRabAjZa6GfDpwjXw5smRhrElJwAAAIEA
r50yi3hHawNnb5qgYLXhN+KA8XJF753eCWHtMw7NR8fz6fjQ1R2J97UjjGuQ8DvwpGeNQ5S+AuIo0rGq
svdg7TTecBcbgBOnR7Fs2+W5HiSVEGbvj1xaeK8fkNE6kaJumBB343b8Rgj0G97MP/os1GfkEqmX9glB
0IOM2mgHHyoAAACAfRir27hHy+fw8CxPlsK0R6cFhxYyd/qYYogXFKYIOPxpLoYrjqODeOFThU7TJuBz
aS97eXiruzbffHwzUGfXgmQT5o9IMZRTClWPA/5Ju4O9YABYHccUghf0W+QtgGOT6FOSvBh8uOV0kcHC
GMJAP8omphauZJlc+wgFxhnkyh4=
bitcount:1024
fingerprint:
44:91:32:1f:7a:d1:83:3c:f3:5e:db:53:0a:2d:ce:69
**************************************
mcs-srvr43(config)# no ssh key rsa
mcs-srvr43(config)# show ssh key
**************************************
could not retrieve rsa key information
**************************************
dsa Keys generated:Sun Jul 27 15:20:12 2008
ssh-dss AAAAB3NzaC1kc3MAAACBALpdxLjXNS/jcCNY+F1QZV9HegxBEb0DMUmq9bSq2N+KAcvHllEh
GnaiHhqarOlcEKqhLbIbuqtKTCvfa+Y1hBIAhWVjg1UR3/M22jqxnfhnxL5YRc1Q7fcesFax0myayAIU
nXrkO5iwv9XHTu+EInRc4kJ0XrG9SxtLmDe/fi2ZAAAAFQDbRabAjZa6GfDpwjXw5smRhrElJwAAAIEA
r50yi3hHawNnb5qgYLXhN+KA8XJF753eCWHtMw7NR8fz6fjQ1R2J97UjjGuQ8DvwpGeNQ5S+AuIo0rGq
svdg7TTecBcbgBOnR7Fs2+W5HiSVEGbvj1xaeK8fkNE6kaJumBB343b8Rgj0G97MP/os1GfkEqmX9glB
0IOM2mgHHyoAAACAfRir27hHy+fw8CxPlsK0R6cFhxYyd/qYYogXFKYIOPxpLoYrjqODeOFThU7TJuBz
aS97eXiruzbffHwzUGfXgmQT5o9IMZRTClWPA/5Ju4O9YABYHccUghf0W+QtgGOT6FOSvBh8uOV0kcHC
GMJAP8omphauZJlc+wgFxhnkyh4=
bitcount:1024
fingerprint:
44:91:32:1f:7a:d1:83:3c:f3:5e:db:53:0a:2d:ce:69
**************************************
mcs-srvr43(config)# no ssh key dsa
mcs-srvr43(config)# show ssh key
**************************************
could not retrieve rsa key information
**************************************
could not retrieve dsa key information
**************************************
no ssh keys present. you will have to generate them
**************************************You can clear SSH sessions from the device.
Log in to the CLI in EXEC mode.
| Command or Action | Purpose | |
|---|---|---|
| Step 1 |
switch# show users |
Displays user session information. |
| Step 2 |
switch# clear line vty-line |
Clears a user SSH session. |
| Step 3 |
(Optional) switch# show users |
(Optional)
Displays user session information. |
This example shows how to clear an SSH session:
switch# show users
NAME LINE TIME IDLE PID COMMENT
admin tty1 Jul 25 19:13 old 2867
admin pts/0 Jul 28 09:49 00:02 28556 (10.21.148.122)
admin pts/1 Jul 28 09:46 . 28437 (::ffff:10.21.148.122)*
switch# clear line 0
switch# show users
NAME LINE TIME IDLE PID COMMENT
admin tty1 Jul 25 19:13 old 2867
admin pts/1 Jul 28 09:46 . 28437 (::ffff:10.21.148.122)*
mcs-srvr43(config)#
Use the following commands to verify the configuration.
|
Command |
Purpose |
|---|---|
|
show ssh key [dsa | rsa ] |
Displays SSH server key-pair information. |
|
show running-config security [all ] |
Displays the SSH and user account configuration in the running configuration. The all keyword displays the default values for the SSH and user accounts. |
|
show ssh server |
Displays the SSH server configuration. |
This example shows how to configure SSH with an OpenSSH key:
Disable the SSH server.
switch# configure terminal
switch(config)# no feature ssh Generate an SSH server key.
switch(config)# ssh key rsa
generating rsa key(1024 bits).....
.generated rsa keyEnable the SSH server.
switch(config)# feature ssh Display the SSH server key.
switch(config)# show ssh key
rsa Keys generated:Sat Sep 29 00:10:39 2007
ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAIEAvWhEBsF55oaPHNDBnpXOTw6+/OdHoLJZKr+MZm99n2U0
ChzZG4svRWmHuJY4PeDWl0e5yE3g3EO3pjDDmt923siNiv5aSga60K36lr39HmXL6VgpRVn1XQFiBwn4
na+H1d3Q0hDt+uWEA0tka2uOtXlDhliEmn4HVXOjGhFhoNE=
bitcount:1024
fingerprint:
51:6d:de:1c:c3:29:50:88:df:cc:95:f0:15:5d:9a:df
**************************************
could not retrieve dsa key information
**************************************Specify the SSH public key in OpenSSH format.
switch(config)# username User1 sshkey ssh-rsa
AAAAB3NzaC1yc2EAAAABIwAAAIEAy19oF6QaZl9G+3f1XswK3OiW4H7YyUyuA50rv7gsEPjhOBYmsi6PAVKui1nIf/
DQhum+lJNqJP/eLowb7ubO+lVKRXFY/G+lJNIQW3g9igG30c6k6+XVn+NjnI1B7ihvpVh7dLddMOXwOnXHYshXmSiH
3UD/vKyziEh5S4Tplx8=Save the configuration.
switch(config)# copy running-config startup-configThis table only includes updates for those releases that have resulted in additions to the feature.
|
Feature Name |
Releases |
Feature Information |
|---|---|---|
|
SSH |
4.0(4)SV1(1) |
This feature was introduced. |
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