What’s a broadcast storm?

In this article, we will discuss about a broadcast storm and its effects and how we can eliminate them.

A Broadcast Storm is basically a situation when an abruptly large number of broadcast packets in a very small amount of time. Due to the broadcast storm, the network quality degrades significantly. It leads to broadcast and multicast traffic accumulation on a computer network.

This condition can lead to consume all the network, so, it will be unable to transfer normal amount of traffic at that time. A Broadcast Packet that leads to such situation is often called Chernobyl Packet.

BROADCAST  STORM

Types of Broadcast Packets :

Mainly, there are 3 types of Broadcast Packets :

• Broadcast
• Multicast
• Unicast

A Broadcast packet uses Air as a medium to transfer the broadcast to any listener at the same frequency. A broadcast packet uses the destination header in the following ways :

• ff-ff-ff-ff-ff-ff (Layer 2 broadcast)
• 255.255.255.255 (Layer 3 broadcast)

Root Causes of a Broadcast Storm :

• When a user wants to connect to a specific hub of network but, by mistake, it gets connected to another switch port. This will catch all the frames and keep them within the loop. For Example – When the computer connects to port while being connected to wireless network also, the network sets to bridging mode.
• Improper VLAN configuration settings can create a loop that finally leads to a broadcast storm.
• Too big Broadcast Domain – If the Broadcast is too big, then the amount of traffic in a domain is directly proportional to size of the broadcast domain, i.e. the number hosts in a L2 VLAN or L3 subnet.
• High Volume of requests for IP address via DHCP –  DHCP is the most easiest way for a networking host to get the IP address from a network controller. DHCP uses either broadcast or unicast packets as their medium. For Example – when the network is back online after a outage, all the members on that network try to obtain the IP address.

Steps to prevent a Broadcast Storm :

• Anti-virus Firewalls can be used to detect and remove malicious and intentionally induced broadcast storms to disrupt the network.
• The more often ARP tables are cleared, the more often broadcast requests occur.
• Storm protocols and equivalent controlling techniques allow to limit the broadcast packets.
• Disable broadcasts on Layer 3 devices. If a storm originated from the WAN, then shutting off IP directed broadcasts will solve the issue.
• Splitting the broadcast domain will help in diverting the broadcast traffic. By creating a new VLAN network, we can divert more than half of the traffic to the other network. It will help in reducing the storms a lot.
• Regular maintenance of Switches ensure that they don’t face any hardware failure.
• Checking for loops in switches help to upstream the unmanaged switch. The unmanaged switches in order to respond to the broadcasts sometimes flood the network with a lot of unnecessary traffic.

To summarize all the above, the following elements play an effective role in creating a broadcast storm:

• Poor network management
• Poor monitoring of the network
• The use of cheap hubs & ports
• Improper network configuration
• The lack of a network diagram design, needed for proper management and to provide guidelines for all network traffic routes

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