#CISCO MAC ADDRESS TABLE ISSUE PC#

The attacker will need just a little bit of time for the MAC address table to fill up. This tool floods a switch with frames that contain random bogus source and destination MAC and IP addresses. In the picture, the attack tool is running on the host with MAC address C. Sooner or later the table will be filled up. Depending on the type of switch, the MAC address table size can be different but is always vulnerable to the flood attack. Network attack tools are generating about 160,000 MAC entries on a switch per minute. When the MAC address table is full, the switch floods all ports with incoming traffic because it cannot find the port number for a particular MAC address in the MAC address table. The network intruder uses the attack tool to flood the switch with a large number of invalid source MAC addresses until the MAC address table fills up. To do this attacker uses network attack tools for MAC. LetвЂ™s get into more detail about filling up the MAC address table. The figure shows how an attacker can use the normal operating characteristics of the switch to stop the switch from operating. In this case, an attacker will use legitimate tools for malicious actions. Picture 4 вЂ“В Switch Mac flooding attack will populate the entire mac address table with bogus mac addresses As a result, the attacker (in our case вЂњPC CвЂќ) can see all the frames sent from a victim host to another host without a MAC address table entry. In this situation switch will broadcasts all received packets to all the machines on the network. The switch then enters into a fail-open mode that means that it starts acting as a hub. MAC flooding makes use of this limitation to send to the switch a whole bunch of fake source MAC addresses until the switch MAC address table is fully loaded and can not save any more MAC address вЂ“ Port mapping entries. The key to understanding how MAC address table overflow attacks work is to know that MAC address tables are limited in size. Picture 3 вЂ“В When the switch learns about all MAC addresses on his different ports switch acts like switch вЂ“ mac address table completeД«ut this is where the attacker is coming into play.

This is the main goal of switch functionality, to have separate collision domain for each port on the switch.

#CISCO MAC ADDRESS TABLE ISSUE PC#

The switch then learns that the MAC address for PC B is located on port 2 and writes that information into the MAC address table.В From now on any frame sent by host A (or any other host) to host B is forwarded to port 2 of the switch and not broadcast out every port. PC B receives the frame and sends a reply to PC A. Picture 2 вЂ“В Switch learns mac address from source MAC address in the layer 2 headers from frames вЂ“ switch is populating his mac table This means that not only PC B receives the frame, PC C also receives the frame from host A to host B, but because the destination MAC address of that frame is host B, host C drops that frame. If the switch does not have the destination MAC in the MAC address table, the switch then copies the frame and sends it out every switch port like a broadcast. The switch receives the frames and looks up the destination MAC address in its MAC address table. Picture 1 вЂ“В Switch acts as hub with empty mac address tableД¬omputer A sends traffic to computer B. If the MAC address does not exist, the switch acts like a hub and forwards the frame out every other port on the switch while learning the MAC for next time. In this case the switch forwards the frame to the MAC address port designated in the MAC address table. If the switch has already learned the MAC address of the computer connected to his particular port then an entry exists for the MAC address. When frames arrive on switch ports, the source MAC addresses are learned from Layer 2 packet header and recorded in the MAC address table. Cisco Catalyst switch models use a MAC address table for Layer 2 switching. When switch receives a frame, he looks in the MAC address table (sometimes called CAM table) for the destination MAC address. To understand the mechanism of a MAC address table overflow attack we must recall how does a switch work in the first place. MAC flooding attacks are sometimes calledВ MAC address table overflow attacks. MAC address table in the switch has the MAC addresses available on a given physical port of a switch and the associated VLAN parameters for each. MAC address flooding attack is very common security attack.

Cisco mac address table issue