Abstract: This article introduces the application of SSH on the H3C S7500 series Ethernet switches in real network environments, and then presents detailed configurations of the involved SSH client and Ethernet switches respectively.

Acronyms: SSH (Secure Shell), RSA (Rivest Shamir Adleman)

Chapter 1 SSH Overview

1.1 Introduction to SSH

Secure Shell (SSH) is designed to provide secure remote login and other security services in insecure network environments. When users remotely access the switch across an insecure network, SSH will automatically encrypt data before transmission and decrypt data after they reach the destination to guarantee information security and protect switches from such attacks as plain-text password interception. In addition, SSH provides powerful authentication to defend against the man-in-the-middle attacks. SSH uses the client/server mode, by which the SSH server accepts the connection requests from SSH clients and provides authentication. SSH clients can establish SSH connections and log into the SSH server through the SSH connections.

SSH also provides other functions, such as compressing the data to be transmitted to speed up the transmission speed, functioning as Telnet, and providing secure channels for FTP, PoP and even PPP.

& Note:

For details about SSH functions supported on Ethernet switches, refer to related user manuals.

1.2 Support for SSH Functions

Currently, an S7500 switch can function as an SSH client or an SSH server.

1.3 SSH Configuration

1.3.1 Configuring an SSH Server

I. For a H3C switch to be the SSH server

l Configure the protocols supported on user interfaces

l Create or destroy an RSA key pair

l Create an SSH user and specify an authentication type

l Specify a service type for the SSH user

l Configure the SSH management function on the SSH server

l Configure a client public key on the SSH server

l Specify a public key for the SSH user

II. For a non H3C device to be the SSH server

For such configuration, refer to the related user manual.

1.3.2 Configuring an SSH Client

I. Using SSH client software

There are many kinds of SSH client software, such as PuTTY and OpenSSH. You can select one as required and refer to the attached manual for configuration.

II. Using an SSH2-capable switch

l Configure whether first-time authentication is supported

l Establish a connection between the SSH client and the SSH server

1.3.3 Precautions

l If you have configured a user interface to support the SSH protocol, you must configure AAA authentication for the user interface by using the authentication-mode scheme command to ensure successful login.

l Creating an RSA key pair on the SSH server is necessary for successful SSH login.

Chapter 2 SSH Configuration Commands

2.1 SSH Configuration Commands

To implement SSH, you need to configure the SSH client and the SSH server correctly.

The subsequent sections describe SSH configuration commands on the switch. For more information, refer to the SSH Operation Manual.

2.2 Configuring an H3C Switch as an SSH Server

2.2.1 Configuration Procedure

Table 2-1 Configure the switch as an SSH server

Role	Common configuration	Authentication type	Public key configuration		Remarks
SSH server	For detailed command, refer to Common configuration.	Password authentication	—		For detailed command, refer to Password authentication configuration.
SSH server	For detailed command, refer to Common configuration.	RSA authentication	Configure a public key manually: copy the public key from the client public key file to the SSH server.	Associate the client public key saved on the SSH server to the SSH client	For detailed commands, refer to Configuring the client RSA public key manually .

I. Precautions for authentication type configuration

The above table introduces the password authentication and RSA authentication separately. In practice, you can combine the two authentication types.

l Executing the ssh authentication-type default password-publickey command or the ssh user authentication-type password-publickey command means that users must not only pass the password authentication but also pass the RSA authentication to login the SSH server.

l Executing the ssh authentication-type default all command or the ssh user authentication-type all command means that users can login the SSH server as long as they pass either the password or RSA authentication.

II. Public key configuration procedure and precautions

As shown in Table 2-1, you need to copy or import the public key from the client to the server.

l When a host acts as the SSH client, use the SSH client program to generate an RSA key pair and display the RSA public key.

l When a switch acts as the SSH client, use the display rsa local-key-pair public command to display the RSA public key after creating RSA key pair through the corresponding commands.

l Manually copy the RSA public key to the SSH server. Thus, the SSH server has the same public key as the SSH client, and can authenticate the SSH client when the SSH client establishes a connection with it.

2.2.2 Configuration Commands

I. Common configuration

Table 2-2 Common configuration

Operation	Command	Remarks
Enter system view	system-view	—
Enter the view of one or multiple user interfaces	user-interface [ type-keyword ] number [ ending-number ]	—
Configure the authentication mode as scheme	authentication-mode scheme [ command-authorization ]	Required By default, the user interface authentication mode is password.
Specify the supported protocol(s)	protocol inbound { all \|ssh \| telnet }	Optional By default, both Telnet and SSH are supported.
Return to the system view	quit	—
Create an RSA key pair	rsa local-key-pair create	Required By default, no RSA key pair is created.
Destroy the RSA key pair	rsa local-key-pair destroy	Optional
Specify a service type for the SSH user	ssh user username service-type { stelnet \| sftp \| all }	Optional stelnet by default
Set SSH authentication timeout time	ssh server timeout seconds	Optional By default, the timeout time is 60 seconds.
Set SSH authentication retry times	ssh server authentication-retries times	Optional By default, the number of retry times is 3.
Set RSA server key update interval	ssh server rekey-interval hours	Optional By default, the system does not update RSA server keys.
Configure SSH server to be compatible with SSH1.x clients	ssh server compatible-ssh1x enable	Optional By default, SSH server is compatible with SSH1.x clients.

II. Password authentication configuration

Table 2-3 Configure password authentication

Operation	Command		Description
Create an SSH User and specify an authentication type	Specify the default authentication type for all SSH users	ssh authentication-type default password	Optional By default, the authentication type is password. Note that: If both commands are used and different authentication types are specified, the authentication type specified with the ssh user authentication-type command takes precedence.
	Specify the default authentication type for all SSH users	ssh user username
	Create an SSH user, and specify an authentication type for the user	ssh user username authentication-type password

& Note:

For common configuration commands, refer to Table 2-2.

III. Configuring the client RSA public key manually

Table 2-4 Configure the client RSA public key manually

Operation	Command		Description
Create an SSH user and specify an authentication type	Specify the default authentication type for all SSH users	ssh authentication-type default rsa	Use either command. By default, the authentication type is password. Note that: If both commands are used and different authentication types are specified, the authentication type specified with the ssh user authentication-type command takes precedence.
	Specify the default authentication type for all SSH users	ssh user username
	Create an SSH user, and specify an authentication type for it	ssh user username authentication-typ rsa
Enter public key view	rsa peer-public-key keyname		Required
Enter public key edit view	public-key-code begin		—
Configure the client RSA public key	Enter the content of the RSA public key		The content must be a hexadecimal string that is generated randomly by the SSH-supported client software and coded compliant to PKCS. Spaces and carriage returns are allowed between characters.
Return from public key code view to public key view	public-key-code end		When you exit public key code view, the system automatically saves the public key.
Return from public key view to system view	peer-public-key end		—
Assign a public key to an SSH user	ssh user username assign rsa-key keyname		Required If you issue this command multiple times, the last command overrides the previous ones

& Note:

For common configuration commands, refer to Table 2-2.

2.3 Configuring an H3C Switch as an SSH Client

When the device connects to the SSH server as an SSH client, you can configure whether the device supports first-time authentication.

l First-time authentication means that when the SSH client accesses the server for the first time and is not configured with the server host public key, the user can continue accessing the server, and will save the host public key on the client for use in subsequent authentications.

l When first-time authentication is not supported, a client, if not configured with the server host public key, will be denied of access to the server. To access the server, a user must configure in advance the server host public key locally and specify the public key name for authentication.

2.3.1 Configuration Procedure

Table 2-5 Configure the switch as an SSH client

Role	Common configuration	First-time authentication support	Public key configuration		Access the SSH server	Remarks
SSH Client	Refer to Common configuration	Yes	—		Establish a connection between the SSH client and the SSH server	Refer to Enabling first-time authentication.
SSH Client	Refer to Common configuration	No	Configure a public key manually: copy the server public key from the public key file to the SSH client	Specify the host public key of the SSH server to be connected		Refer to Disabling first-time authentication.

As shown in Table 2-5, you need to configure the server public key to the client in the case that the SSH client does not support first-time authentication.

l On the SSH server, use the display rsa local-key-pair public command to display the RSA public key.

l Configure the public key to the SSH client. Thus, the SSH client can authenticate the SSH server using the public key when establishing a connection with the SSH server.

2.3.2 Configuration Commands

I. Enabling first-time authentication

Table 2-6 Enable first-time authentication

Operation	Command	Description
Enter system view	system-view	—
Enable first-time authentication	ssh client first-time enable	Optional Enabled by default
Establish a connection with the SSH server	ssh2 { host-ip \| host-name } [ port-num ] [ prefer_kex { dh_group1 \| dh_exchange_group } \| prefer_ctos_cipher { des \| aes128 } \| prefer_stoc_cipher { des \| aes128 } \| prefer_ctos_hmac { sha1 \| sha1_96 \| md5 \| md5_96 } \| prefer_stoc_hmac { sha1 \| sha1_96 \| md5 \| md5_96 } ] *	Required In this command, you can also specify the preferred key exchange algorithm, encryption algorithms and HMAC algorithms between the server and client.

II. Disabling first-time authentication

Table 2-7 Disable first-time authentication

Operation	Command	Description
Enter system view	system-view	—
Disable first-time authentication	undo ssh client first-time	Required Enabled by default
Enter public key view	rsa peer-public-key keyname	Required
Enter public key edit view	public-key-code begin	—
Configure server public key	Enter the content of the public key	When you input the key data, spaces are allowed between the characters you input (because the system can remove the spaces automatically); you can also press <Enter> to continue your input at the next line. But the key you input should be a hexadecimal digit string coded in the public key format.
Return to public key view from public key edit view	public-key-code end	When you exit public key code view, the system automatically saves the public key
Exit public key view and return to system view	peer-public-key end	—
Specify the host key name of the server	ssh client { server-ip \| server-name } assign rsa-key keyname	Optional Required when the SSH client does not support first-time authentication You need to copy the server public key to the SSH client before performing this configuration.
Start the client to establish a connection with an SSH server	ssh2 { host-ip \| host-name } [ port-num ] [ prefer_kex { dh_group1 \| dh_exchange_group } \| prefer_ctos_cipher { des \| aes128 } \| prefer_stoc_cipher { des \| aes128 } \| prefer_ctos_hmac { sha1 \| sha1_96 \| md5 \| md5_96 } \| prefer_stoc_hmac { sha1 \| sha1_96 \| md5 \| md5_96 } ] *	Required In this command, you can also specify the preferred key exchange algorithm, encryption algorithms and HMAC algorithms between the server and client.

Chapter 3 SSH Configuration Examples

& Note:

The S7500 software version in this configuration example is Release 3135.

3.1 SSH Configuration Examples

3.1.1 When the Switch Acts as the SSH Server and the Authentication Type is Password

I. Network requirements

As shown in Figure 3-1, establish an SSH connection between the host (SSH Client) and the switch (SSH Server) for secure data exchange. The host runs SSH2.0 client software. Password authentication is required.

II. Network diagram

Figure 3-1 Network diagram of SSH server configuration using password authentication

III. Configuration procedure

1) Configure the SSH server

# Create a VLAN interface on the switch and assign an IP address, which the SSH client will use to connect with the SSH server.

<H3C> system-view

[H3C] interface vlan-interface 1

[H3C-Vlan-interface1] ip address 192.168.0.1 255.255.255.0

[H3C-Vlan-interface1] quit

# Generate an RSA key pair.

[H3C] rsa local-key-pair create

The key name will be: H3C_Host

The range of public key size is (512 ~ 2048).

NOTES: If the key modulus is greater than 512,

It will take a few minutes.

Input the bits in the modulus[default = 1024]:

Generating keys...

..............++++++

............................++++++

...........................................++++++++

.................++++++++

.........

# Set the authentication mode for the user interface to AAA.

[H3C] user-interface vty 0 4

[H3C-ui-vty0-4] authentication-mode scheme

# Enable the user interface to support SSH.

[H3C-ui-vty0-4] protocol inbound ssh

[H3C-ui-vty0-4] quit

# Create local client “client001”, and set the authentication password to “abc”, protocol type to SSH, and command privilege level to 3 for the client.

[H3C] local-user client001

[H3C-luser-client001] password simple abc

[H3C-luser-client001] service-type ssh level 3

[H3C-luser-client001] quit

Caution:

This example configures the server to use local authentication, therefore the AAA scheme referenced by the ISP domain must be a local authentication scheme. Otherwise, the client cannot log into the server.

# Specify the authentication type for user “client001” as password.

[H3C] ssh user client001 authentication-type password

2) Configure the SSH client

# Configure an IP address (192.168.0.2 in this case) for the SSH client. This IP address and that of the VLAN interface on the switch must be in the same network segment.

# Configure the SSH client software to establish a connection to the SSH server.

Take SSH client software “Putty” (version 0.58) as an example:

l Run PuTTY.exe to enter the following configuration interface.

Figure 3-2 SSH client configuration interface

In the Host Name (or IP address) text box, enter the IP address of the SSH server.

l From the category on the left pane of the window, select SSH under Connection. The window as shown in Figure 3-3 appears.

Figure 3-3 SSH client configuration interface 2

Under Protocol options, select 2 from Preferred SSH protocol version.

l As shown in Figure 3-4, click Open to enter the following interface. If the connection is normal, you will be prompted to enter the user name “client001” and password “abc”. Once authentication succeeds, you will log onto the server.

Figure 3-4 SSH client interface