Packet Tracer – Layer 2 Security
• Assign the Central switch as the root bridge.
• Secure spanning-tree parameters to prevent STP manipulation attacks.
• Enable port security to prevent CAM table overflow attacks.
Background / Scenario
There have been a number of attacks on the network recently. For this reason, the network administrator has assigned you the task of configuring Layer 2 security.
For optimum performance and security, the administrator would like to ensure that the root bridge is the 3560 Central switch. To prevent spanning-tree manipulation attacks, the administrator wants to ensure that the STP parameters are secure. To prevent against CAM table overflow attacks, the network administrator has decided to configure port security to limit the number of MAC addresses each switch port can learn. If the number of MAC addresses exceeds the set limit, the administrator would like the port to be shutdown.
All switch devices have been preconfigured with the following:
• Enable password: ciscoenpa55
• Console password: ciscoconpa55
• SSH username and password: SSHadmin / ciscosshpa55
Part 1: Configure Root Bridge
Step 1: Determine the current root bridge.
From Central, issue the show spanning-tree command to determine the current root bridge, to see the ports in use, and to see their status.
Which switch is the current root bridge?
Based on the current root bridge, what is the resulting spanning tree? (Draw the spanning-tree topology.)
Step 2: Assign Central as the primary root bridge.
Using the spanning-tree vlan 1 root primary command, and assign Central as the root bridge.
Step 3: Assign SW-1 as a secondary root bridge.
Assign SW-1 as the secondary root bridge using the spanning-tree vlan 1 root secondary command.
Step 4: Verify the spanning-tree configuration.
Issue the show spanning-tree command to verify that Central is the root bridge.
Central# show spanning-tree VLAN0001 Spanning tree enabled protocol ieee Root ID Priority 24577 Address 00D0.D31C.634C This bridge is the root Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Which switch is the current root bridge?
Based on the new root-bridge, what is the resulting spanning tree? (Draw the spanning-tree topology.)
Part 2: Protect Against STP Attacks
Secure the STP parameters to prevent STP manipulation attacks.
Step 1: Enable PortFast on all access ports.
PortFast is configured on access ports that connect to a single workstation or server to enable them to become active more quickly. On the connected access ports of the SW-A and SW-B, use the spanning-tree portfast command.
Step 2: Enable BPDU guard on all access ports.
BPDU guard is a feature that can help prevent rogue switches and spoofing on access ports. Enable BPDU guard on SW-A and SW-B access ports.
Note: Spanning-tree BPDU guard can be enabled on each individual port using the spanning-tree bpduguard enable command in interface configuration mode or the spanning-tree portfast bpduguard default command in global configuration mode. For grading purposes in this activity, please use the spanning-tree bpduguard enable command.
Step 3: Enable root guard.
Root guard can be enabled on all ports on a switch that are not root ports. It is best deployed on ports that connect to other non-root switches. Use the show spanning-tree command to determine the location of the root port on each switch.
On SW-1, enable root guard on ports F0/23 and F0/24. On SW-2, enable root guard on ports F0/23 and F0/24.
Part 3: Configure Port Security and Disable Unused Ports
Step 1: Configure basic port security on all ports connected to host devices.
This procedure should be performed on all access ports on SW-A and SW-B. Set the maximum number of learned MAC addresses to 2, allow the MAC address to be learned dynamically, and set the violation to shutdown.
Note: A switch port must be configured as an access port to enable port security.
Why is port security not enabled on ports that are connected to other switch devices?
Step 2: Verify port security.
a. On SW-A, issue the command show port-security interface f0/1 to verify that port security has been configured.
SW-A# show port-security interface f0/1 Port Security : Enabled Port Status : Secure-up Violation Mode : Shutdown Aging Time : 0 mins Aging Type : Absolute SecureStatic Address Aging : Disabled Maximum MAC Addresses : 2 Total MAC Addresses : 0 Configured MAC Addresses : 0 Sticky MAC Addresses : 0 Last Source Address:Vlan : 0000.0000.0000:0 Security Violation Count : 0
b. Ping from C1 to C2 and issue the command show port-security interface f0/1 again to verify that the switch has learned the MAC address for C1.
Step 3: Disable unused ports.
Disable all ports that are currently unused.
Step 4: Check results.
Your completion percentage should be 100%. Click Check Results to view feedback and verification of which of the required components have been completed.