1. How to Configure VLAN Hopping for Cisco Switch http://www.router-switch.com/

2. VLAN Hopping  VLAN hopping (virtual local area network hopping) is a method of attacking a network by sending packets to a port that is not normally accessible from a given end system.  The basic concept behind all VLAN hopping attacks is for an attacking host on a VLAN to gain access to traffic on other VLANs that would normally not be accessible. There are two primary methods of VLAN hopping: switch spoofing and double tagging. Following the easy steps to configure VLAN Hopping for Cisco Switches on Attack Prevention.

4.  Switch-1 (config)# vtp mode server  Switch-1 (config)# vtp domain rt  Switch-1 (config)#vtp pruning  Switch-1 (config)#vtp version 2  Switch-1 (config)#vtp password cisco  Switch-1(config)# vlan 99  Switch-1(config)# vlan 10  Switch-1(config-vlan)# name yanfa  Switch-1(config)#interface fastethernet 0/1  Switch-1(config-if)# switchport mode access  Switch-1(config-if)# switchport access vlan 10  Switch-1(config)# vlan 20  Switch-1(config-vlan)# name renshi  Switch-1(config)#interface fastethernet 0/2  Switch-1(config-if)# switchport mode access  Switch-1(config-if)# switchport access vlan 20  Switch-1(config)#interface fastethernet 0/24  Switch-1(config-if)#shutdown  Switch-1(config-if)#switchport trunk encapsulation dot1q  Switch-1(config-if)#switchport trunk allowed vlan 99,10,20  Switch-1(config-if)#switchport mode trunk  Switch-1(config-if)#switchport trunk native vlan 99  Switch-1(config-if)#switchport nonegotiate  Switch-1(config-if)#no shutdown

5.  Switch-2 (config)#vtp domain rt  Switch-2 (config)#vtp password cisco  Switch-2 (config)#vtp pruning  Switch-2 (config)#vtp version 2  Switch-2 (config)#vtp mode client  Switch-2(config)#interface fastethernet 0/1  Switch-2 (config-if)# switchport mode access  Switch-2 (config-if)# switchport access vlan 10  Switch-2(config)#interface fastethernet 0/2  Switch-2 (config-if)# switchport mode access  Switch-2 (config-if)# switchport access vlan 20  Switch-2(config)#interface fastethernet 0/24  Switch-2(config-if)#shutdown  Switch-2(config-if)#switchport trunk encapsulation dot1q  Switch-2(config-if)#switchport trunk allowed vlan 99,10,20  Switch-2(config-if)#switchport mode trunk  Switch-2(config-if)#switchport trunk native vlan 99  Switch-2(config-if)#switchport nonegotiate  Switch-2(config-if)#no shutdown

6. VLAN Hopping Function  VLAN hopping can be used to steal passwords and other sensitive information from specific network subscribers. VLAN hopping can also be used to modify, corrupt, or delete data, install spyware or other malware programs, and propagate viruses, worms, and Trojans throughout a network.  This example can be applied to all the Cisco switches, like Catalyst 2960, 3560 series switch, Cisco 3750X, 3850 Cisco, etc.Catalyst 29603560 series switchCisco 3750X

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