CCNA Security Lab: Securing Layer 2 Switches

CCNA Security Lab: Securing Layer 2 Switches

Topology
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IP 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
S1 VLAN 1              192.168.1.2 255.255.255.0 N/A N/A
S2 VLAN 1              192.168.1.3 255.255.255.0 N/A N/A
PC-A NIC                     192.168.1.10 255.255.255.0 192.168.1.1 S1 FA0/6
PC-B NIC                     192.168.3.11 255.255.255.0 192.168.1.1 S2 FA0/18

Objectives

Part 1: Configure Basic Switch Settings

  • Build the topology.
  • Configure the host name, IP address, and access passwords.

Part 2: Configure SSH Access to the Switches

  • Configure SSH access on the switch.
  • Configure an SSH client to access the switch.
  • Verify the configuration.

Part 3: Secure Trunks and Access Ports

  • Configure trunk port mode.
  • Change the native VLAN for trunk ports.
  • Verify trunk configuration.
  • Enable storm control for broadcasts.
  • Configure access ports.
  • Enable PortFast and BPDU guard.
  • Verify BPDU guard.
  • Enable root guard.
  • Configure port security.
  • Verify port security.
  • Disable unused ports.

Part 4: Configure SPAN and Monitor Traffic

  • Configure Switched Port Analyzer (SPAN).
  • Monitor port activity using Wireshark.
  • Analyze a sourced attack.

Background
The Layer 2 (Data Link) infrastructure consists mainly of interconnected Ethernet switches. Most end-user devices, such as computers, printers, IP phones and other hosts, connect to the network via Layer 2 access switches. As a result, they can present a network security risk. Similar to routers, switches are subject to attack from malicious internal users. The switch Cisco IOS software provides many security features that are specific to switch functions and protocols.

In this lab, you configure SSH access and Layer 2 security for switches S1 and S2. You also configure various switch protection measures, including access port security, switch storm control, and Spanning Tree Protocol (STP) features such as BPDU guard and root guard. Lastly, you use Cisco SPAN to monitor traffic to specific ports on the switch.

Note: The router commands and output in this lab are from a Cisco 1841 with Cisco IOS Release 12.4(20)T (Advanced IP image). The switch commands and output are from a Cisco WS-C2960-24TT-L with Cisco IOS Release 12.2(46)SE (C2960-LANBASEK9-M image). Other routers, switches, and IOS versions may be used. See the Router Interface Summary table at the end of the lab to determine which interface identifiers to use based on the equipment in the lab. Depending on the router or switch model and IOS version, the commands available and output produced might vary from what is shown in this lab.

Note: Make sure that the router and the switches have been erased and have no startup configurations.

Instructor Note: Instructions for erasing switches and routers are provided in the Lab Manual, located on Academy Connection in the Tools section.

Required Resources

  • One router (Cisco 1841 with Cisco IOS Release 12.4(20)T1 or comparable)
  • Two switches (Cisco 2960 or comparable with cryptography IOS image for SSH support – Release 12.2(46)SE or comparable)
  • PC-A (Windows XP or Vista with a PuTTY SSH client and Wireshark)
  • PC-B (Windows XP or Vista with a PuTTY SSH client and SuperScan)
  • Ethernet cables as shown in the topology
  • Rollover cables to configure the switches via the console

Instructor Notes:

  • This lab is divided into four parts. Each part can be administered individually or in combination with others as time permits. The focus is configuring security measures on switches S1 and S2. Router R1 serves as a realistic gateway connection and is mainly used to change the MAC address connected to switch S1 for port security testing.
  • Students can work in teams of two for switch configuration, one person configuring S1 and the other configuring S2.
  • The basic running configs for the router and two switches are captured after Parts 1 and 2 of the lab are completed. The running config for S1 and S2 are captured after Parts 3 and 4 and are listed separately. All configs are found at the end of the lab.

Part 1: Basic Device Configuration

In Part 1 of this lab, you set up the network topology and configure basic settings such as the host names, IP addresses, and device access passwords.

Note: Perform all tasks on router R1 and switches S1 and S2. The procedure for S1 is shown here as an example.

Step 1: Cable the network as shown in the topology.
Attach the devices shown in the topology diagram and cable as necessary.

Step 2: Configure basic settings for the router and each switch.
a. Configure host names as shown in the topology.

b. Configure interface IP addresses as shown in the IP Addressing Table. The configuration of the VLAN 1 management interface on switch S1 is shown here.

c. Configure the enable secret and console passwords.

Note: Do not configure the switch vty access at this time. The vty lines are configured on the switches in Part 2 for SSH access.

d. Configure the vty lines and password on R1.

e. To prevent the router or switch from attempting to translate incorrectly entered commands, disable DNS lookup. Router R1 is shown here as an example.

f. HTTP access to the switch is enabled by default. To prevent HTTP access, disable the HTTP server and HTTP secure server.

Note: The switch must have a cryptography IOS image to support the ip http secure-server command. HTTP access to the router is disabled by default.

Step 3: Configure PC host IP settings.
Configure a static IP address, subnet mask, and default gateway for PC-A and PC-B as shown in the IP Addressing Table.

Step 4: Verify basic network connectivity.
a. Ping from PC-A and PC-B to the R1 Fa0/1 interface at IP address 192.168.1.1. Were the results successful?
Yes. If the pings are not successful, troubleshoot the basic device configurations before continuing.

b. Ping from PC-A to PC-B. Were the results successful?
Yes. If the pings are not successful, troubleshoot the basic device configurations before continuing.

Step 5: Save the basic configurations for the router and both switches.
Save the running configuration to the startup configuration from the privileged EXEC prompt.

Part 2: SSH Configuration

In Part 2 of this lab, you configure switches S1 and S2 to support SSH connections and install SSH client software on the PCs.

Note: A switch IOS image that supports encryption is required to configure SSH. Otherwise, you cannot specify SSH as an input protocol for the vty lines and the crypto commands are not available.

Task 1: Configure the SSH Server on Switch S1 and S2 Using the CLI
In this task, use the CLI to configure the switch to be managed securely using SSH instead of Telnet. Secure Shell (SSH) is a network protocol that establishes a secure terminal emulation connection to a switch 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.

Note: For a switch to support SSH, it must be configured with local authentication, AAA services or username. In this task, you configure an SSH username and local authentication on S1 and S2. S1 is shown here as an example.

Step 1: Configure a domain name.
Enter global configuration mode and set the domain name.

Step 2: Configure a privileged user for login from the SSH client.

a. Use the username command to create the user ID with the highest possible privilege level and a secret password.

b. Exit to the initial switch login screen, and log in with this username. What was the switch prompt after you entered the password? The privileged EXEC (enable) prompt # sign. With a privilege level of 15, the login defaults to privileged EXEC mode.

Step 3: Configure the incoming vty lines.
a. Configure vty access on lines 0 through 4. Specify a privilege level of 15 so that a user with the highest privilege level (15) will default to privileged EXEC mode when accessing the vty lines. Other users will default to user EXEC mode. Specify the use of local user accounts for mandatory login and validation, and accept only SSH connections.

Step 4: Generate the RSA encryption key pair for the router.
The switch uses the RSA key pair for authentication and encryption of transmitted SSH data. Configure the RSA keys with 1024 for the number of modulus bits. The default is 512, and the range is from 360 to 2048.

Instructor Note: The details of encryption methods are covered in Chapter 7.

Step 5: Verify the SSH configuration.

a. Use the show ip ssh command to see the current settings.

b. Fill in the following information based on the output of the show ip ssh command.
SSH version enabled: Most likely 1.5 to 1.99
Authentication timeout: Default is 120 seconds
Authentication retries: Default is 3 tries

Step 6: Configure SSH timeouts and authentication parameters.

The default SSH timeouts and authentication parameters can be altered to be more restrictive using the following commands.

Task 2: Configure the SSH Client

TeraTerm and PuTTY are two terminal emulation programs that can support SSHv2 client connections. This lab uses PuTTY.

Step 1: (Optional) Download and install an SSH client on PC-A and PC-B.
If the SSH client is not already installed, download either TeraTerm or PuTTY.

Note: The procedure described here is for PuTTY and pertains to PC-A.

Step 2: Verify SSH connectivity to S1 from PC-A.

a. Launch PuTTY by double-clicking the putty.exe icon.

b. Input the S1 IP address 192.168.1.2 in the Host Name or IP address field.

c. Verify that the SSH radio button is selected. PuTTY defaults to SSH version 2.

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d. Click Open.

e. In the PuTTY Security Alert window, click Yes.

f. Enter the admin username and password cisco12345 in the PuTTY window.
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g. At the S1 privileged EXEC prompt, enter the show users command.

What users are connected to switch S1 at this time? You should see at least two users, one for your console connection and another for the SSH interface.

h. Close the PuTTy SSH session window with the exit or quit command.

i. Try to open a Telnet session to switch S1 from PC-A. Were you able to open the Telnet session? Why or why not?
No, the Telnet session fails because only SSH is enabled as input for the vty lines.

Step 3: Save the configuration.

Save the running configuration to the startup configuration from the privileged EXEC prompt.

Part 3: Secure Trunks and Access Ports

In Part 3 of this lab, you configure trunk ports, change the native VLAN for trunk ports, verify trunk configuration, and enable storm control for broadcasts on the trunk ports. Securing trunk ports can help stop VLAN hopping attacks. The best way to prevent a basic VLAN hopping attack is to turn off trunking on all ports except the ones that specifically require trunking. On the required trunking ports, disable DTP (auto trunking) negotiations and manually enable trunking. If no trunking is required on an interface, configure the port as an access port. This disables trunking on the interface.

Note: Tasks should be performed on switches S1 or S2 as indicated.

Task 1: Secure Trunk Ports

Step 1: Configure switch S1 as the root switch.

For the purposes of this lab, assume that switch S2 is currently the root bridge and that switch S1 is preferred as the root switch. To force S1 to become the new root bridge, you configure a new priority for it.

a. From the console on S1, enter privileged EXEC mode and then global configuration mode.

b. The default priority for switches S1 and S2 is 32769 (32768 + 1 with System ID Extension). Set S1 priority to 0 so that it becomes the root switch.

c. Issue the show spanning-tree command to verify that S1 is the root bridge and to see the ports in use and their status.

d. What is the S1 priority? 1 (priority 0 plus sys-id-ext 1)

e. What ports are in use and what is their status? Fa0/1, Fa0/5 and Fa0/6. All are FWD (forwarding)

Step 2: Configure trunk ports on S1 and S2.

a. Configure port Fa0/1 on S1 as a trunk port.

b. Configure port Fa0/1 on S2 as a trunk port.

c. Verify that S1 port Fa0/1 is in trunking mode with the show interfaces trunk command.

Step 3: Change the native VLAN for the trunk ports on S1 and S2.
Changing the native VLAN for trunk ports to an unused VLAN helps prevent VLAN hopping attacks.

a. From the output of the show interfaces trunk in the previous step, what is the current native VLAN for the S1 Fa0/1 trunk interface? It is set to the default VLAN 1.

b. Set the native VLAN on the S1 Fa0/1 trunk interface to an unused VLAN 99.

c. The following message should be displayed after a brief period of time. 02:16:28: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on FastEthernet0/1 (99), with S2 FastEthernet0/1 (1). What does the message mean? The S1 Fa0/1 native VLAN is now 99, but the S2 native VLAN is still 1. Both ends of the trunk must share the same native VLAN for trunking to occur.

d. Set the native VLAN on the S2 Fa0/1 trunk interface to VLAN 99.

Step 4: Prevent the use of DTP on S1 and S2.
Setting the trunk port to not negotiate also helps to mitigate VLAN hopping by turning off the generation of DTP frames.

Step 5: Verify the trunking configuration on port Fa0/1.

Step 6: Enable storm control for broadcasts.

Enable storm control for broadcasts on the trunk port with a 50 percent rising suppression level using the storm-control broadcast command.

Step 7: Verify your configuration with the show run command.
Use the show run command to display the running configuration, beginning with the first line that has the text string “0/1” in it.

Task 2: Secure Access Ports
By manipulating the STP root bridge parameters, network attackers hope to spoof their system, or a rogue switch that they add to the network, as the root bridge in the topology. If a port that is configured with PortFast receives a BPDU, STP can put the port into the blocking state by using a feature called BPDU guard.

Step 1: Disable trunking on S1 access ports.

a. On S1, configure Fa0/5, the port to which R1 is connected, as access mode only.

b. On S1, configure Fa0/6, the port to which PC-A is connected, as access mode only.

c. On S2, configure Fa0/18, the port to which PC-B is connected, as access mode only.

Task 3: Protect Against STP Attacks
The topology has only two switches and no redundant paths, but STP is still active. In this step, you enable some switch security features that can help reduce the possibility of an attacker manipulating switches via STP-related methods.

Step 1: Enable PortFast on S1 and S2 access ports.
PortFast is configured on access ports that connect to a single workstation or server to enable them to become active more quickly.

a. Enable PortFast on the S1 Fa0/5 access port.

The following Cisco IOS warning message is displayed:

b. Enable PortFast on the S1 Fa0/6 access port.

c. Enable PortFast on the S2 Fa0/18 access ports

Step 2: Enable BPDU guard on the S1 and S2 access ports.
BPDU guard is a feature that can help prevent rogue switches and spoofing on access ports.

a. Enable BPDU guard on the switch ports previously configured as access only.

b. PortFast and BPDU guard can also be enabled globally with the spanning-tree portfast

default and spanning-tree portfast bpduguard commands in global configuration mode.

Note: BPDU guard can be enabled on all access ports that have PortFast enabled. These ports should never receive a BPDU. BPDU guard is best deployed on user-facing ports to prevent rogue switch network extensions by an attacker. If a port enabled with BPDU guard receives a BPDU, it is disabled and must be manually re-enabled. An err-disable timeout can be configured on the port so that it can recover automatically after a specified time period.

c. Verify that BPDU guard is configured by using the show spanning-tree interface fa0/5 detail command on switch S1.

Step 3: (Optional) Enable root guard.
Root guard is another option in helping to prevent rogue switches and spoofing. Root guard can be enabled on all ports on a switch that are not root ports. It is normally enabled only on ports connecting to edge switches where a superior BPDU should never be received. Each switch should have only one root port, which is the best path to the root switch.

a. The following command configures root guard on S2 interface Gi0/1. Normally, this is done if another switch is attached to this port. Root guard is best deployed on ports that connect to switches that should not be the root bridge.

b. Issue the show run command to verify that root guard is configured.

Note: The S2 Gi0/1 port is not currently up, so it is not participating in STP. Otherwise, you could use
the show spanning-tree interface Gi0/1 detail command.

c. If a port that is enabled with BPDU guard receives a superior BPDU, it goes into a root-inconsistent state. Use the show spanning-tree inconsistentports command to determine if there are any ports currently receiving superior BPDUs that should not be.

Note: Root guard allows a connected switch to participate in STP as long as the device does not try to become the root. If root guard blocks the port, subsequent recovery is automatic. If the superior BPDUs stop, the port returns to the forwarding state.

Task 4: Configure Port Security and Disable Unused Ports
Switches can also be subject to CAM table overflow, MAC spoofing attacks, and unauthorized connections to switch ports. In this task, you configure port security to limit the number of MAC addresses that can be learned on a switch port and disable the port if that number is exceeded.

Step 1: Record the R1 Fa0/0 MAC address.

a. From the router R1 CLI, use the show interface command and record the MAC address of the interface.

b. What is the MAC address of the R1 Fa0/1 interface? In the example above, it is 001b.5325.256f

Step 2: Configure basic port security.

This procedure should be performed on all access ports that are in use. Switch S1 port Fa0/5 is shown here as an example.

Note: A switch port must be configured as an access port to enable port security.

a. From the switch S1 CLI, enter interface configuration mode for the port that connects to the router (Fast Ethernet 0/5).

b. Shut down the switch port.

c. Enable port security on the port.

Note: Entering just the switchport port-security command sets the maximum MAC addresses to 1 and the violation action to shutdown. The switchport port-security maximum and switchport port-security violation commands can be used to change the default behavior.

d. Configure a static entry for the MAC address of R1 Fa0/1/ interface recorded in Step 1.

Note: Optionally, you can use the switchport port-security mac-address sticky

command to add all the secure MAC addresses that are dynamically learned on a port (up to the maximum set) to the switch running configuration.

e. Bring up the switch port.

Step 3: Verify port security on S1 Fa0/5.

a. On S1, issue the show port-security command to verify that port security has been configured on S1 Fa0/5.

b. What is the status of the Fa0/5 port? Secure-up, which indicates that the port is secure but the status and protocol are up.
What is the Last Source Address and VLAN? 001b.5325.256f:1, the MAC address of R1 Fa0/1 and VLAN 1.

c. From the router R1 CLI, ping PC-A to verify connectivity. This also ensures that the R1 Fa0/1 MAC address is learned by the switch.

d. You will now violate security by changing the MAC address on the router interface. Enter interface configuration mode for the Fast Ethernet 0/1 interface and shut it down.

e. Configure a MAC address for the interface on the interface, using aaaa.bbbb.cccc as the address.

f. Enable the Fast Ethernet 0/1 interface.

g. From the router R1 CLI, ping PC-A. Was the ping successful? Why or why not? No, the Fa0/5 port on switch S1 shut down because of the security violation.

h. On switch S1 console, observe the messages when port Fa0/5 detects the violating MAC address.

violation occurred, caused by MAC address aaaa.bbbb.cccc on port FastEthernet0/5.

i. On the switch, use the various show port-security commands to verify that port security has been violated.

j. On the router, shut down the Fast Ethernet 0/1 interface, remove the hard-coded MAC address from the router, and re-enable the Fast Ethernet 0/1 interface.

Note: This will restore the original FastEthernet interface MAC address.

k. From R1, try to ping the PC-A again at 192.168.1.10. Was the ping successful? Why or why not?
No, the S1 Fa0/5 port is still in an err-disabled state.

Step 4: Clear the S1 Fa0/5 error disabled status.

a. From the S1 console, clear the error and re-enable the port using the following commands. This will change the port status from Secure-shutdown to Secure-up.

Note: This assumes the device/interface with the violating MAC address has been removed and replaced with the one originally configured.

b. From R1, ping PC-A again. You should be successful this time.

Step 5: Remove basic port security on S1 Fa0/5.

a. From the S1 console, remove port security on Fa0/5. This procedure can also be used to re-enable the port but port security commands will need to be reconfigured.

b. You can also use the following commands to reset the interface to its default settings.

Note: This default interface command also requires you to reconfigure the port as an access port in order to re-enable the security commands.

Step 6: (Optional) Configure port security for VoIP.

The following example shows a typical port security configuration for a voice port. Two MAC addresses are allowed, and they are to be learned dynamically. One MAC address is for the IP phone, and the other IP address is for the PC connected to the IP phone. Violations of this policy result in the port being shut down. The aging timeout for the learned MAC addresses is set to two hours. This example is shown for switch S2 port Fa0/18.

Step 7: Disable unused ports on S1 and S2.

As a further security measure, disable any ports not being used on the switch.

a. Ports Fa0/1, Fa0/5, and Fa0/6 are used on switch S1. The remaining Fast Ethernet ports and the two Gigabit Ethernet ports will be shutdown.

b. Ports Fa0/18 and Gi0/1 are used on switch S2. The remaining Fast Ethernet ports and the Gigabit Ethernet ports will be shutdown.

Step 8: (Optional) Move active ports to a VLAN other than the default VLAN 1

As a further security measure, you can move all active end user and router ports to a VLAN other than the default VLAN 1 on both switches.
a. Configure a new VLAN for users on each switch using the following commands:

b. Add the current active access (non-trunk) ports to the new VLAN.

Note: This will prevent communication between end user hosts and the management VLAN IP address of the switch, which is currently VLAN 1. The switch can still be accessed and configured using the console connection.

If you need to provide Telnet or SSH access to the switch, a specific port can be designated as the management port and added to VLAN 1 with a specific management workstation attached. A more elaborate solution is to create a new VLAN for switch management (or use the existing native trunk VLAN 99) and configure a separate subnet for the management and user VLANs. Enable trunking with subinterfaces on R1 to route between the management and user VLAN subnets.

Part 4: Configure SPAN and Monitor Traffic

Note: There are two tasks in this part of the lab, Task 1: Option 1 is to be performed using hands-on equipment. Task 2: Option 2 is modified to be compatible with the NETLAB+ system but can also be performed using hands-on equipment.

Cisco IOS provides a feature that can be used to monitor network attacks called Switched Port Analyzer (SPAN). Cisco IOS supports local SPAN and remote SPAN (RSPAN). With local SPAN, the source VLANs, source switch ports, and the destination switch ports are on the same physical switch. In this part of the lab, you configure a local SPAN to copy traffic from one port where a host is connected to another port where a monitoring station is connected. The monitoring station will run the Wireshark packet sniffer application to analyze traffic.

Note: SPAN allows you to select and copy traffic from one or more source switch ports or source VLANs onto one or more destination ports.

Task 1: Option 1 – Configure a SPAN Session Using Hands-on Equipment.

Note: Option 1 assumes you have physical access to the devices shown in the topology for this lab. NETLAB+ users accessing lab equipment remotely should proceed to Task 2: Option 2.

Step 1: Configure a SPAN session on S1 with a source and destination

a. Set the SPAN source interface using the monitor session command in global configuration mode. The following configures a SPAN source port on FastEthernet 0/5 for ingress and egress traffic. Traffic copied on the source port can be ingress only, egress only or both. Switch S1 port Fa0/5 is connected to router R1, so traffic to (ingress) and from (egress) switch port Fa0/5 to R1 will be monitored.

Note: You can specify to monitor tx (transmit) or rx (receive) traffic. The keyword both includes tx and rx. The source can be a single interface, a range of interfaces, a single VLAN, or a range of VLANs.

b. Set the SPAN destination interface.

All traffic from S1 Fa0/5, where R1 is connected, will be copied to the SPAN destination port Fa0/6, where PC-A with Wireshark is connected.

Note: The destination can be an interface or a range of interfaces.

Step 2: Verify the setup of the SPAN session on S1.

Confirm the SPAN session setup.

Step 3: (Optional) Download and install Wireshark on PC-A.

a. Wireshark is a network protocol analyzer (also called a packet sniffer) that runs with Windows XP and Vista. If Wireshark is not currently available on PC-A, you can download the latest version from http://www.wireshark.org/download.html. This lab uses Wireshark version 1.0.5. The initial Wireshark installation screen is shown here.

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b. Click I Agree to the License agreement and accept the defaults by clicking Next when prompted.

Note: On the Install WinPcap screen, select the install WinPcap options and select Start WinPcap service option if you want to have other users besides those with administrative privileges run Wireshark.

Step 4: Monitor switch S1 port Fa0/5 ping activity using Wireshark on PC-A.

a. If Wireshark is available, start the application.

b. From the main menu, select Capture > Interfaces.
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c. Click the Start button for the local area network interface adapter with IP address 192.168.1.10.
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d. Generate some traffic from PC-B (192.168.1.11) to R1 interface Fa0/1 (192.168.1.1) using ping. This traffic will go from S2 port Fa0/18 to S2 port Fa0/1 across the trunk link to S1 port Fa0/1 and then exit interface Fa0/5 on S1 to reach R1. PC-B:\>ping 192.168.1.1

e. Observe the results in Wireshark on PC-A. Notice the initial ARP request broadcast from PC-B (Intel NIC) to determine the MAC address of the R1 Fa0/1 interface with IP address 192.168.1.1 and the ARP reply from the R1 Cisco Ethernet interface. After the ARP request, the pings (echo request and replies) can be seen going from PC-B to R1 and from R1 to PC-B through the switch.

Note: Your screen should look similar to the one below. Some additional packets might be captured in addition to the pings, such as the R1 Fa0/1 LOOP reply.
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Step 5: Monitor switch S1 port Fa0/5 SuperScan activity using Wireshark on PC-A.

a. If SuperScan is not on PC-B, download the SuperScan 4.0 tool from the Scanning Tools group at http://www.foundstone.com. Unzip the file into a folder. The SuperScan4.exe file is executable and installation is not required.

b. Start the SuperScan program on PC-B. Click the Host and Service Discovery tab. Check the Timestamp Request check box, and uncheck the Echo Request check box. Scroll through the UDP and TCP port selection lists and notice the range of ports that will be scanned.

c. In the SuperScan program, click the Scan tab and enter the IP address R1 FA0/1 (192.168.1.1) in the Hostname/IP field.

d. Click the right arrow to populate the Start IP and End IP fields.

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e. Clear the previous capture in Wireshark and start a new capture by clicking Capture > Start. When prompted, click the Continue without saving button.

f. In the SuperScan program, click the blue arrow button in the lower left to start the scan.

g. Observe the results in the Wireshark window on PC-A. Notice the number and types of ports tried by the simulated SuperScan attack from PC-B (192.168.1.11) to R1 Fa0/1 (192.168.1.1). Your screen should look similar to the following:

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Task 2: Option 2 – Configure a SPAN Session Using NETLAB+ Remote Equipment.

Note: This portion of the lab has been rewritten to enhance compatibility with the NETLAB+ system. On switch S1, you will configure a local SPAN to reflect the traffic exiting Port Fa0/5, in this case, the traffic from PC-A to R1’s Fa0/1. This traffic should be received by switch S2, and forwarded to PC-B, where Wireshark is capturing the packets. Refer to the following diagram which illustrates the SPAN traffic flow.

Note: To perform this Task, Wireshark should be installed on PC-B.
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Note: Switch S2 is acting as a regular switch, forwarding frames based on destination MAC addresses and switch ports. The traffic entering S2 through Port Fa0/1 utilizes the R1’s MAC address as destination for the Ethernet frame, therefore in order to forward those packets to PC-B, the R1’s MAC address must be the same as PC-B. To accomplish this, R1’s Fa0/1 MAC address is modified using the IOS CLI to simulate PC-B’s MAC address. This requirement is specific to the NETLAB+ environment.

Step 1: Configure a SPAN session on S1 with Source and Destination:

a. Return the Fa0/1 on S1 and S2 to its default configuration. This link S1 Fa0/1 to S2 Fa0/1 is going to be used to carry the traffic being monitored.

b. Write down the MAC address for PC-B

c. Configure the PC-B’s MAC address on R1’s Fa0/1.

d. Set the SPAN Source Interface using the monitor session command in global configuration mode.
The following configures a SPAN source port on fastethernet0/5 for egress traffic. Traffic copied on the source port can be ingress only, egress only or both. In this case, the egress traffic is the only one analyzed. On Switch S1 port Fa0/5 is connected to router R1 so traffic to the switch port Fa0/5 to R1 will be monitored.

Note: The source can be a single interface, a range of interfaces, a single VLAN, or range of VLANs.

e. Set the SPAN destination interface.

All egress traffic from S1 Fa0/5, where R1 is connected, will be copied to the SPAN destination port Fa0/1, where PC-B with WireShark is connected.

Note: The destination can be an interface or a range of interfaces.

Step 2: Verify the setup of the SPAN session on S1.

Confirm the SPAN session setup using the show monitor session 1 command.

Step 3: (Optional) Download and install Wireshark on PC-B

a. WireShark is a network protocol analyzer (also called a packet sniffer) that runs with Windows XP and Vista. If WireShark is not currently available on PC-B, you may download the latest version from http://www.wireshark.org/download.html and install it as described in Part 4, Task 1, Step 3.

Step 4: Monitor Switch S1 port Fa0/5 ping activity using Wireshark on PC-B

a. If WireShark is available, start the application.

b. From the main menu, select Capture > Interfaces.

c. Click the Start button for the Local area network interface adapter.

d. Generate some traffic from PC-A (192.168.1.10) to R1 interface Fa0/1 (192.168.1.1) using ping. This traffic will go from S1 port Fa0/6 to S1 port Fa0/5. In addition, the traffic going from PC-A to R1 interface Fa0/1 is forwarded across the link between S1 and S2, and then S2 will forward this traffic to PC-B, where Wireshark is capturing the packets. Before pinging, delete the ARP table on PC-A, so an ARP request would be generated. Note that the SPAN session is configured only on S1, and S2 is operating as a normal switch.

C:\>arp –d *
C:\>ping 192.168.1.1

e. Observe the results in WireShark on PC-B. Notice the initial ARP request broadcast from PC-A to determine the MAC address of the R1 Fa0/1 interface with IP address 192.168.1.1 and the ARP reply from the R1 Cisco Ethernet interface. After the ARP request the pings (echo requests) can be seen going from PC-A to R1 through the switch.

Note: Your screen should look similar to the one below. There may be some addition packets captured, in addition to the pings, such as the R1 Fa0/1 LOOP Reply and Spanning Tree Packets.

ccna-security-lab-securing-layer-2-switches-10
Step 5: Monitor Switch S1 port Fa0/5 SuperScan activity using Wireshark on PC-B

a. If SuperScan is not on PC-A, download the SuperScan 4.0 tool from the Scanning Tools group at http://www.foundstone.com. Unzip the file into a folder. The SuperScan4.exe file is executable and installation is not required.

b. Start the SuperScan program on PC-A. Click the Host and Service Discovery tab. Check the Timestamp Request check box and uncheck the Echo Request check box. Scroll the UDP and TCP port selection lists and notice the range of ports that will be scanned.

c. In the SuperScan program click the Scan tab and enter the IP address of R1 FA0/1 (192.168.1.1) in the Hostname/IP field.

d. Click the right facing arrow to populate the Start and End IP fields.
ccna-security-lab-securing-layer-2-switches-11

e. Clear the previous capture in WireShark and start a new capture by clicking Capture > Start and when prompted click the Continue without saving button.

f. In the SuperScan program click the button which is in the lower left of the screen, with the blue arrow on it, to start the scan.

g. Observe the results on the WireShark window on PC-B. Notice the number and types of ports tried by the simulated SuperScan attack from PC-A (192.168.1.11) to R1 Fa0/1 (192.168.1.1). Your screen should look similar the following:
ccna-security-lab-securing-layer-2-switches-12

Step 6: Reflection.

a. Why should port security be enabled on switch access ports? Answers will vary, but should include that port security allows a limited number of hosts to use the port and a PC cannot be connected and use the network without authorization.

b. Why should port security be enabled on switch trunk ports? Answers will vary, but should include trunk security can help to prevent VLAN hopping and STP attacks from rogue switches.

c. Why should unused ports on a switch be disabled? Answers will vary, but should include that an unauthorized device cannot be plugged into an unused switch port and use the network, because the unused ports have to be administratively enabled to be utilized.

Router Interface Summary Table

Router Interface Summary
Router Model Ethernet Interface
#1
Ethernet Interface
#2
Serial Interface
#1
Serial Interface
#2
1700 Fast Ethernet 0
(Fa0)
Fast Ethernet 1
(Fa1)
Serial 0 (S0) Serial 1 (S1)
1800 Fast Ethernet 0/0
(Fa0/0)
Fast Ethernet 0/1
(Fa0/1)
Serial 0/0/0
(S0/0/0)
Serial 0/0/1
(S0/0/1)
2600 Fast Ethernet 0/0
(Fa0/0)
Fast Ethernet 0/1
(Fa0/1)
Serial 0/0 (S0/0) Serial 0/1 (S0/1)
2800 Fast Ethernet 0/0
(Fa0/0)
Fast Ethernet 0/1
(Fa0/1)
Serial 0/0/0
(S0/0/0)
Serial 0/0/1
(S0/0/1)
Note: To find out how the router is configured, look at the interfaces to identify the type of router and how many interfaces the router has. Rather than list all combinations of configurations for each router class, this table includes identifiers for the possible combinations of Ethernet and serial interfaces in the device. The table does not include any other type of interface, even though a specific router might contain one. For example, for an ISDN BRI interface, the string in parenthesis is the legal abbreviation that can be used in Cisco IOS commands to represent the interface.

Device Configs

Router R1 after Part 1

Switch S1 after Parts 1 and 2

Switch S2 after Parts 1 and 2

Switch S1 after Parts 3 and 4

Switch S2 after Parts 3 and 4

More Resources

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