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What Is A Broadcast
Storm?
This is when a large number of broadcast packets happen at the
same time. For example, when a power failure causes a significant
number of machines to reboot at the same time, each machine
broadcasts a question at the same time (such as “who has
this IP address?”), causing a “storm” of packets.
This can bring the network down again... and again... and again.
An alternate scenario is one involving redundant layer 2 connections
between switches running a spanning tree. In normal operation,
the switches select one of the connections to be the active
one and disable the alternate path. When the primary path fails,
the alternate path can be activated and connectivity is maintained.
If the spanning tree protocol is somehow disabled, a broadcast
storm results: any broadcast packet received on one of the redundant
connections is rebroadcast to all interfaces EXCEPT the interface
on which it was received. The obvious problem is that one of
these interfaces leads to back to the switch that originally
sent the packet – which now loops the packet back to first
switch. Very quickly, these switches amplify the original broadcast
packet and spend all their time resending the same broadcast,
creating a broadcast storm. Thus, to protect the network against
broadcast storms, some links are rate limited.
Back
to Case Study
t
is a cakebox? It is a small, inexpensive PC
running Linux. It is configured such that, when you plug it
into a DHCP-enabled Ethernet port and give it power, it registers
its presence with an LDAP server where it logs its current
IP address so you can “find” it. You can then
connect to it remotely and run a series of network utilities
(like Iperf, traceroute, and pchar). Cakeboxes were developed
by Internet2 to test H.323 video conferencing capabilities
and have been used for a variety of other end-to-end performance
tests. Instructions on “building” a cakebox are
available to member institutions upon request.
DHCP-enabled Ethernet port and give it power, it registers
its presence with an LDAP server where it logs its current
IP address so you can “find” it. You can then
connect to it remotely and run a series of network utilities
(like Iperf, traceroute, and pchar). Cakeboxes were developed
by Internet2 to test H.323 video conferencing capabilities
and have been used for a variety of other end-to-end performance
tests. Instructions on “building” a cakebox are
available to member institutions upon request.
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