Broadcast Storm

8/4/2019 Broadcast Storm

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WHAT IS BROADCAST STORM?

A state in which a message that has been broadcast

across a network results in even more responses,

and each response results in still more responses in

a snowball effect. A severe broadcast storm can block all other

network traffic, resulting in a network meltdown.

Broadcast storms can usually be prevented bycarefully configuring a network to block illegal

broadcast messages.


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Network meltdown:

- A state in which a network grinds to a halt due to

excessive traffic.

Broadcast:- Broadcasting sends a message to everyone on the network.

Snowball effect:

- Snowball effect is a figurative term for a process that starts

from an initial state of small significance and builds uponitself, becoming larger and perhaps potentially dangerous or

disastrous though it might be beneficial instead.


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Imagine that Node B is connected to Switch A, and needs

to communicate with Node A on Segment B. Switch A

does not know who Node A is, so it floods the packet.

The packet travels via Segment A or Segment C to theother two switches (B and C).

Switch B will add Node B to the lookup table it maintains

for Segment A, while Switch C will add it to the lookup

table for Segment C.

If neither switch has learned the address for Node A yet,

they will flood Segment B looking for Node A.


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Each switch will take the packet sent by the other

switch and flood it back out again immediately, since

they still don't know who Node A is.

Switch A will receive the packet from each segmentand flood it back out on the other segment.

This causes a broadcast storm as the packets are

broadcast, received and rebroadcast by each switch,

resulting in potentially severe network congestion.


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DECTECTING BROADCAST STORM

An informal way,

You may suspect that a broadcast storm isoccurring when your network response times

become extremely slow and networkoperations are timing out

As a broadcast storm progresses, userscannot log in to servers or access e-mail. As

the storm worsens, the network becomesunusable.


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STORM CONTROL

It's important to protect your organization'sLAN from broadcast storms, which can causenetwork slowdowns if they become severe.

With the Cisco IOS, you can easily and quicklyprotect your network by configuring a singlecommand on each switch interface.


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STORM CONTROL

Storm control, manages how the receiving porthandles the broadcast.

By default, the switch only drops the broadcastpackets. In addition, you can shut down the port orsend a SNMP ( simple network managementprotocol ) trap to your management station.

EG: Switch(config)# int fa0/19Switch(config-if)#storm-control broadcast level 50Switch(config-if)# storm-control action trap

(catalyst 2950)


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AVOIDING BROADCAST STORM

Spanning Tree Protocol (STP), defined instandard 802.1D, will eliminate network loopsuntil an active link loses connectivity.

When this happens, Spanning Tree willautomatically reconfigure the network to usethe redundant path.


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STP

Spanning Tree Protocol (STP) is standardizedas IEEE 802.1D.

As the name suggests, it creates a spanning

tree within a mesh network of connected layer-2 bridges (typically Ethernet switches).

Disables those links that are not part of the

spanning tree, leaving a single active pathbetween any two network nodes.


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Broadcast Storm

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