Principles of Fraggle attacks

Attack introduction:
Similar to smurf, UDP is used to respond to messages instead of ICMP. UDP port 7 (ECHO) and port 19 (chargen) respond after receiving UDP packets. After UDP port 7 receives the packet, it will respond to the received content, while UDP port 19 generates a string of RST streams after receiving the packet. Like ICMP, these messages generate a large number of useless response packets, occupying the network bandwidth. Attackers can send UDP packets whose source address is the victim network or host to the subnet broadcast address. The port number is 7 or 19. each system that enables this function in the sub-network responds to the victim's host, resulting in a large number of packets, leading to network congestion or host crash; A system that does not enable these functions on the subnet will generate an ICMP inaccessible message, which still consumes bandwidth. You can also change the source port to Chargen. The target port is echo, which will automatically generate response packets continuously, which is more harmful.
Solution:
Check the UDP packet that enters the firewall. If the destination port number is 7 or 19, the packet is rejected and the attack is recorded in the log. Otherwise, the packet passes.

Principles of Fraggle attacks