Layer 2 Security
发表时间:2010-10-12 评论:0 点击 3,261+
Topology Diagram
Objectives
Assign the Central switch as the root bridge.
Secure spanning-tree parameters to prevent STP manipulation attacks.
Enable storm control to prevent broadcast storms.
Enable port security to prevent MAC address table overflow attacks.
Introduction
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 against spanning-tree manipulation attacks, the administrator
wants to ensure that the STP parameters are secure. In addition, the network
administrator would like to enable storm control to prevent broadcast storms. Finally,
to prevent against MAC address table overflow attacks, the network administrator has
decided to configure port security to limit the number of MAC addresses that can be
learned
per switch port. If the number of MAC addresses exceeds the set limit, the administrator
would like for the port to be shutdown.
All switch devices have been preconfigured with the following:
Enable password: ciscoenpa55
Console password: ciscoconpa55
VTY line password: ciscovtypa55
Task 1: Configure Root Bridge
S tep 1. Determin e the c u rrent ro o t bridge.
From Central, issue the show spanning-tree command to determine the current root bridge
and to see the ports in use and their status.
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.)
S tep 2. A s s ign C entra l as the prima r y ro o t bridge.
Using the spanning-tree vlan 1 root primary command, assign the 3560 Central switch as
the root bridge.
Central(config)# spanning-tree vlan 1 root primary
S tep 3. A ss ign SW -1 a s a s ec o nda r y ro o t 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
S tep 4. V er ify the s pa nning-tree c o nfigu ra tio n .
Issue the show spanning-tree command to verify that 3560 Central switch is the root
bridge. 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.)
Task 2: Protect Against STP Attacks
Secure the STP parameters to prevent STP manipulation attacks.
S tep 1. E na ble P o rtF a s t o n a ll a c c es s po rts .
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 switches, use the spanning-tree portfast command.
SW-A(config)# interface range fastethernet 0/1 – 4
SW-A(config-if-range)# spanning-tree portfast
SW-B(config)# interface range fastethernet 0/1 – 4
SW-B(config-if-range)# spanning-tree portfast
S tep 2. E nable B P D U gu ard o n all ac c es s po rts .
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 fastethernet 0/1 – 4
SW-A(config-if-range)# spanning-tree bpduguard enable
SW-B(config)# interface range fastethernet 0/1 – 4
SW-B(config-if-range)# spanning-tree bpduguard enable
Note: Spanning-tree bpduguard can be enabled on each individual port using the command
spanning-tree bpduguard enable, or in global configuration mode with the command
spanning-tree portfast bpduguard default. For grading purposes, in this activity please
use the spanning-tree bpduguard enable command.
S tep 3. E na ble ro o t gu a rd.
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 switch SW-1, enable root guard on ports Fa0/23 and Fa0/24. On switch SW-2, enable
root guard on ports
Fa0/23 and Fa0/24.
SW-1(config)# interface fa0/23
SW-1(config-if)# spanning-tree guard root
SW-1(config-if)# interface fa0/24
SW-1(config-if)# spanning-tree guard root
SW-2(config)# interface fa0/23
SW-2(config-if)# spanning-tree guard root
SW-2(config-if)# interface fa0/24
SW-2(config-if)# spanning-tree guard root
Task 3: Enable Storm Control
S tep 1. E na ble s to rm c o ntro l fo r bro a dc a s ts .
Enable storm control for broadcasts on all ports connecting switches (trunk ports). Set
a 50 percent rising suppression level using the storm-control broadcast command. Enable
storm-control on interfaces connecting Central, SW-1, and SW-2.
Example:
SW-1(config)# interface gi1/1
SW-1(config-if)# storm-control broadcast level 50
SW-1(config-if)# interface fa0/1
SW-1(config-if)# storm-control broadcast level 50
SW-1(config-if)# interface fa0/23
SW-1(config-if)# storm-control broadcast level 50
SW-1(config-if)# interface fa0/24
SW-1(config-if)# storm-control broadcast level 50
**Repeat on SW-2 (gig1/1, fa0/1, fa0/23, and fa0/24) and Central (gig0/1, gig0/2, fa0/1)
connection to other switches
S tep 2. V er ify s to rm c o ntro l c o nfigu ra tio n .
Verify your configuration with the show storm-control broadcast command and the show run
command.
Task 4: Configure Port Security and Disable Unused Ports
S tep 1. C o nfigu re ba s ic po rt s ec u rity o n a ll po rts c o nn ec ted to ho s t
dev ic es .
This procedure should be performed on all access ports on SW-A and SW-B. Set the maximum
number of learned MAC address to 2, allow the MAC address to be learned dynamically, and
set the violation to shut- down.
Keep in mind that a switch port must be configured as an access port to enable port
security.
Example:
SW-A(config)# interface FastEthernet 0/1
SW-A(config-if)# switchport mode access
SW-A(config-if)# switchport port-security
SW-A(config-if)# switchport port-security maximum 2
SW-A(config-if)# switchport port-security violation shutdown
SW-A(config-if)# switchport port-security mac-address sticky
**Repeat on other ports in SW-A and SW-B
Why would you not want to enable port-security on ports connected to other switches or
routers?
Ports connected to other switch devices and routers can, and should, have a multitude of
MAC addresses learned for that single port. Limiting the number of MAC addresses that
can be learned on these ports can significantly impact network functionality.
S tep 2. V er ify po rt s ec u rity .
On SW-A, issue the show port-security interface fa0/1 command to verify that port
security has been configured.
S tep 3. Dis a ble u nu s ed po rts .
Disable all ports that are currently unused. For efficiency purposes, the Activity
Wizard will only grade Fa0/5 and Fa0/6 on SW-A and SW-B.
Example:
SW-A(config)# interface FastEthernet 0/5
SW-A(config-if)# shutdown
**Repeat on other ports on SW-A and SW-B
S tep 4. C hec 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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