Types of Layer 2/Switch Security Attacks, and Mitigation steps in Brief

Security Attacks against Switches or at Layer 2 can be grouped in four major Categories as follows:
1. MAC layer attacks
2. VLAN attacks
3. Spoofing attacks
4. Attacks on switch devices
1. MAC Layer Attacks Types
MAC address flooding 
Description :- Frames with unique, invalid source MAC addresses flood the switch, exhausting content addressable memory (CAM) table space, disallowing new entries from valid hosts. Traffic to valid hosts is subsequently flooded out all ports.
Mitigation Port security. MAC address VLAN access maps.
2. VLAN Attacks
i – VLAN hopping
By altering the VLAN ID on packets encapsulated for trunking, an attacking device can send or receive packets on various VLANs, bypassing Layer 3 security measures.
Mitigation  Tighten up trunk configurations and the negotiation state of unused ports. Place unused ports in a common VLAN.
ii – Attacks between devices on a common VLAN 
Devices might need protection from one another, even though they are on a common VLAN. This is especially true on service-provider segments that support devices from multiple customers.
Mitigation : – Implement private VLANs (PVLAN).
3. Spoofing Attacks
i – DHCP starvation and DHCP spoofing
An attacking device can exhaust the address space available to the DHCP servers for a period of time or establish itself as a DHCP server in man-in-themiddle attacks.
Mitigation :- Use DHCP snooping.
ii – Spanning-tree compromises 
Attacking device spoofs the root bridge in the STP topology. If successful, the network attacker can see a variety of frames.
Mitigation :- Proactively configure the primary and backup root devices. Enable root guard.
iii – MAC spoofing
Attacking device spoofs the MAC address of a valid host currently in the CAM table. The switch then forwards frames destined for the valid host to the attacking device.
Mitigation :- Use DHCP snooping, port security.
iv – Address Resolution Protocol (ARP) spoofing
Attacking device crafts ARP replies intended for valid hosts. The attacking device’s MAC address then becomes the destination address found in the Layer 2 frames sent by the valid network device.
Mitigation :- Use Dynamic ARP Inspection, DHCP snooping, port security.
4. Switch Device Attacks
i – Cisco Discovery Protocol (CDP) manipulation
Information sent through CDP is transmitted in clear text and unauthenticated, allowing it to be captured and divulge network topology information.
Mitigation :- Disable CDP on all ports where it is not intentionally used.
ii – Secure Shell Protocol (SSH) and Telnet attacks
Telnet packets can be read in clear text. SSH is an option but has security issues in version 1.
Mitigation : – Use SSH version 2. Use Telnet with vty ACLs.


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