14.9.10 Packet Tracer – Implement STP Security Answers

14.9.10 Packet Tracer – Implement STP Security Answers Version

Topology

14.9.10 Packet Tracer - Implement STP Security Answers 4

Objectives

  • Assign the Central switch as the root bridge.
  • Secure spanning-tree parameters to prevent STP manipulation 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.

All switch devices have been preconfigured with the following:

  • Enable password: ciscoenpa55
  • Console password: ciscoconpa55
  • SSH username and password: SSHadmin / ciscosshpa55

Instructions

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.

Question:

Which switch is the current root bridge?
Current root is SW-1.
Based on the current root bridge, what is the resulting spanning tree? (Draw the spanning-tree topology.)
14.9.10 Packet Tracer - Implement STP Security Answers 5

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.

Central(config)# spanning-tree vlan 1 root primary
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.

SW-1(config)# spanning-tree vlan 1 root secondary
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

Questions:

Which switch is the current root bridge?
Current root is Central.
Based on the new root-bridge, what is the resulting spanning tree? (Draw the spanning-tree topology.)
14.9.10 Packet Tracer - Implement STP Security Answers 6

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.

SW-A(config)# interface range f0/1 – 4

SW-A(config-if-range)# spanning-tree portfast

SW-B(config)# interface range f0/1 – 4

SW-B(config-if-range)# spanning-tree portfast
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.

SW-A(config)# interface range f0/1 – 4

SW-A(config-if-range)# spanning-tree bpduguard enable

SW-B(config)# interface range f0/1 – 4

SW-B(config-if-range)# spanning-tree bpduguard enable

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.

SW-1(config)# interface range f0/23 – 24

SW-1(config-if-range)# spanning-tree guard root

SW-2(config)# interface range f0/23 – 24

SW-2(config-if-range)# spanning-tree guard root

Answer Script

Central

spanning-tree vlan 1 root primary

SW-1

spanning-tree vlan 1 root secondary

interface range f0/23 – 24

spanning-tree guard root

SW-2

interface range f0/23 – 24

spanning-tree guard root

SW-A

interface range f0/1 – 4

spanning-tree portfast

spanning-tree bpduguard enable

SW-B

interface range f0/1 – 4

spanning-tree portfast

spanning-tree bpduguard enable

Download 14.9.10 Packet Tracer – Implement STP Security .PDF & PKA files:


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