Configure Cisco Routers for Syslog, NTP, and SSH Operations

作者:admin发表时间:2010-9-12 评论:0 点击 3,108+

Topology Diagram

Addressing Table

Device Interface IP Address Subnet Mask Default Gateway Switch Port
R1 FA0/1 192.168.1.1 255.255.255.0 N/A S1 FA0/5
S0/0/0 (DCE) 10.1.1.1 255.255.255.252 N/A N/A
R2 S0/0/0 10.1.1.2 255.255.255.252 N/A N/A
S0/0/1 (DCE) 10.2.2.2 255.255.255.252 N/A N/A
R3 FA0/1 192.168.3.1 255.255.255.0 N/A S3 FA0/5
S0/0/1 10.2.2.1 255.255.255.252 N/A N/A
PC-A NIC 192.168.1.5 255.255.255.0 192.168.1.1 S1 FA0/6
PC-B NIC 192.168.1.6 255.255.255.0 192.168.1.1 S2 FA0/18
PC-C NIC 192.168.3.5 255.255.255.0 192.168.3.1 S3 FA0/6

Learning Objectives

Configure routers as NTP clients.

Configure routers to update the hardware clock using NTP.

Configure routers to log messages to the syslog server.

Configure routers to timestamp log messages.

Configure local users.

Configure VTY lines to accept SSH connections only.

Configure RSA key pair on SSH server.

Verify SSH connectivity from PC client and router client.

Introduction

The network topology shows three routers. You will configure NTP and Syslog on all routers. You will configure

SSH on R3.

Network Time Protocol (NTP) allows routers on the network to synchronize their time settings with an NTP server. A group of NTP clients that obtain time and date information from a single source have more consistent time settings and Syslog messages generated can be analyzed more easily. This can help when troubleshooting issues with network problems and attacks. When NTP is implemented in the network, it can be set up to synchronize to a private master clock, or to a publicly available NTP server on the Internet.

The NTP Server is the master NTP server in this lab. You will configure the routers to allow the software clock to be synchronized by NTP to the time server. Also, you will configure the routers to periodically update the hardware clock with the time learned from NTP. Otherwise, the hardware clock will tend to gradually lose or

gain time (drift) and the software clock and hardware clock may become out of synchronization with each other.

The Syslog Server will provide message logging in this lab. You will configure the routers to identify the remote host (Syslog server) that will receive logging messages.

You will need to configure timestamp service for logging on the routers. Displaying the correct time and date in Syslog messages is vital when using Syslog to monitor a network. If the correct time and date of a message is not known, it can be difficult to determine what network event caused the message.

R2 is an ISP connected to two remote networks: R1 and R3. The local administrator at R3 can perform most router configurations and troubleshooting; however, since R3 is a managed router, the ISP needs access to R3 for occasional troubleshooting or updates. To provide this access in a secure manner, the administrators have agreed to use Secure Shell (SSH).

You use the CLI to configure the router to be managed securely using SSH instead of Telnet. SSH is a network protocol that establishes a secure terminal emulation connection to a router or other networking device. SSH encrypts all information that passes over the network link and provides authentication of the remote computer. SSH is rapidly replacing Telnet as the remote login tool of choice for network professionals.

The servers have been pre-configured for NTP and Syslog services respectively. NTP will not require authentication. The routers have been pre-configured with the following:

Enable password: ciscoenpa55

Password for vty lines: ciscovtypa55

Static routing

Task 1: Configure routers as NTP Clients.

S tep 1. T es t C o nnec tiv ity

Ping from PC-C to R3.

Ping from R2 to R3.

Telnet from PC-C to R3. Exit the Telnet session.

Telnet from R2 to R3. Exit the Telnet session.

S tep 2. C o nfigu re R 1, R 2 a nd R 3 a s N T P c lients .


R1(config)# ntp server 192.168.1.5
R2(config)# ntp server 192.168.1.5
R3(config)# ntp server 192.168.1.5

Verify client configuration using the command show ntp status.

S tep 3. C o nfigu re ro u ter s to u pda te ha rdwa re c lo c k .

Configure R1, R2 and R3 to periodically update the hardware clock with the time learned from NTP.

R1(config)# ntp update-calendar R2(config)# ntp update-calendar R3(config)# ntp update-calendar

Verify that the hardware clock was updated using the command show clock.

S tep 4. C o nfigu re ro u ter s to time s ta mp lo g me s s a ge s .

Configure timestamp service for logging on the routers.

R1(config)# service timestamps log datetime msec R2(config)# service timestamps log datetime msec R3(config)# service timestamps log datetime msec

Task 2: Configure routers to log messages to the Syslog Server.

S tep 1. C o nfigu re the ro u te rs to identify the remo te ho s t (S y s lo g S e rv er) tha t will re c eiv e lo gging mes s a g es .


R1(config)# logging host 192.168.1.6
R2(config)# logging host 192.168.1.6
R3(config)# logging host 192.168.1.6

The router console will display a message that logging has started.

S tep 2. V er ify lo gging c o nfigu r a tio n u s ing the c o mma nd s ho w lo gging. S tep 3. E x a m ine lo gs o f the S y s lo g s erv er .

From the Config tab of the Syslog server’s dialogue box, select the Syslog services button. Observe the logging messages received from the routers.

Note: Log messages can be generated on the server by executing commands on the router. For example, entering and exiting global configuration mode will generate an informational configuration message.

Task 3: Configure R3 to support SSH connections.

S tep 1. C o nfigu re a do ma in na me .

Configure a domain name of ccnasecurity.com on R3.

R3(config)# ip domain-name ccnasecurity.com

S tep 2. C o nfigu re u s e rs fo r lo gin fro m the S S H c lient o n R 3.

Create a user ID of SSHadmin with the highest possible privilege level and a secret password of

ciscosshpa55.

R3(config)# username SSHadmin privilege 15 secret ciscosshpa55

S tep 3. C o nfigu re the inc o ming VT Y lines o n R 3.

Use the local user accounts for mandatory login and validation. Accept only SSH connections.


R3(config)# line vty 0 4
R3(config-line)# login local
R3(config-line)# transport input ssh

S tep 4. E ra s e ex is ting k e y pa ir s o n R 3.

Any existing RSA key pairs should be erased on the router.

R3(config)#crypto key zeroize rsa

Note: If no keys exist, you might receive this message: % No Signature RSA Keys found in configuration.

S tep 5. G enera te the R S A enc r y ptio n k e y pa ir fo r R 3.

The router uses the RSA key pair for authentication and encryption of transmitted SSH data. Configure the RSA

keys with a modulus of 1024. The default is 512, and the range is from 360 to 2048.

R3(config)# crypto key generate rsa [Enter]

The name for the keys will be: R3.ccnasecurity.com

Choose the size of the key modulus in the range of 360 to 2048 for your General Purpose Keys. Choosing a key modulus greater than 512 may take a few minutes.

How many bits in the modulus [512]:1024

% Generating 1024 bit RSA keys, keys will be non-exportable…[OK]

Note: The command to generate RSA encryption key pairs for R3 in Packet Tracer differs from those used in the lab.

S tep 6. V erify the SSH c o nfigu ra tio n .

Use the show ip ssh command to see the current settings. Verify that the authentication timeout and retries are at their default values of 120 and 3.

S tep 7. Co nfigu re S S H tim eo u ts a nd a u thentic a tio n pa ra m eters .

The default SSH timeouts and authentication parameters can be altered to be more restrictive. Set the timeout to 90 seconds, the number of authentication retries to 2, and the version to 2.


R3(config)# ip ssh time-out 90
R3(config)# ip ssh authentication-retries 2
R3(config)# ip ssh version 2

Issue the show ip ssh command again to confirm that the values have been changed.

S tep 8. A ttempt to c o nne c t to R 3 v ia T elnet fro m P C -C.

Open the Desktop of PC-C. Select the Command Prompt icon. From PC-C, enter the command to connect to

R3 via Telnet.


PC> telnet 192.168.3.1

This connection should fail, since R3 has been configured to accept only SSH connections on the virtual terminal lines.

S tep 9. C o nnec t to R 3 u s ing S S H o n P C -C.

Open the Desktop of PC-C. Select the Command Prompt icon. From PC-C, enter the command to connect to R3 via SSH. When prompted for the password, enter the password configured for the administrator ciscosshpa55.


PC> ssh –l SSHadmin 192.168.3.1

S tep 10. C o nnec t to R 3 u s ing S S H o n R 2.

In order to troubleshoot and maintain the R3 router, the administrator at the ISP must use SSH to access the router CLI. From the CLI of R2, enter the command to connect to R3 via SSH version 2 using the SSHadmin user account. When prompted for the password, enter the password configured for the administrator: ciscosshpa55.


R2# ssh –v 2 –l SSHadmin 10.2.2.1

S tep 11. Chec k res u lts .

Your completion percentage should be 100%. Click Check Results to see feedback and verification of which required components have been completed.

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