Broadcast Storm eWhitepaper 2012

1. Whitepaper www.korenix.com
Disaster to Industrial Ethernet Networking
Root Causes and Solutions
Broadcast Storm

2. Whitepaper www.korenix.com
With Ethernet growing popular as an
Industrial application protocol, more and
more users suffer from broadcast storm
especially when a redundant ring technology
is used in their networks. Broadcast storm,
which overwhelms the network and damages
the whole system, is considered as one of the
most serious problems in Ethernet
networking.
This whitepaper reveals the root cause of
broadcast storm, and presents how to get
free from broadcast storm by korenix’s
comprehensive solution: Prevention,
Resilience, and Protection.
Preface
2
Index
1. The Root Cause
4. When Broadcast Storm Happens to
Redundant Ring
5. Mitigating Broadcast Storm
6. Korenix Comprehensive Solution
a) Prevention within a Ring
b) Resilience to RM failure
c) Protection beyond a Ring
7. Summary
2. The Result: Worse Than You Think
3. Is Your Redundant Ring Safe?

3. Whitepaper www.korenix.com
Eve
Ann Bob
Cat Dan
• Ethernet switch learns how to forward Unicast (1-to-1)
packet according to the destination address of the packet.
• Managed switch learns how to forward Multicast (1-to-
many) packets on demand by the management features.
• Broadcast (1-to-all) packets are flooded everywhere.
BBBBBMMDCBA
• Broadcast packets are transmitted everywhere. If a
network has a loop topology, a broadcast packet goes
through the loop again and again.
• Endless looping broadcast packets consume all the
bandwidth, overwhelming the network in an instance.
B
Ethernet Switching Principle
Looping Broadcast Causes Storm
Root Cause: Loop Topology
3

4. Whitepaper www.korenix.com
Three rings in a LAN share the same broadcast domain
L2
Result: Worse Than You Think
• Unknown Unicast and Unknown Multicast are packets
that switches have not learned how to forward them yet.
These packets are handled as in the same way as
broadcast which may result in storm as well.
Not only Broadcast Packets Cause Storm
• Broadcast packets are flooded everywhere,
thus a storm will radiate from the origin to
the whole network.
• Broadcast is received by all network devices.
Endless broadcast traffic created by a storm
overwhelms every node in the system.
Crash The Whole System
Eve
Ann Bob
Cat Dan
?????
Multicast is commonly used in Industrial protocols such as Ethernet/IP, ProfitNet RT,
IEEE 1588, IEC6850-3 GOOSE, video streaming, and so on.
Industrial Ethernet packet sizes are typically small. A 100Mbps fast Ethernet device might possibly
receive more than 100,000 packets within one second when broadcast storm occurs.
4
Broadcast
Storm

5. Whitepaper www.korenix.com
Is Your Redundant Ring Safe?
Redundant ring technologies are widely used in today’s
industrial Ethernet networks. However, they are essentially
exposed to the risk of broadcast storm because of their
loop topology by nature.
• The technology relies on one and only one switch
assigned as Ring Manager (RM) to monitor the
completeness of the ring
• If the ring is complete, RM blocks one of its path
• The blocked path works for redundancy. It also cuts off
the loop to prevent broadcast storm
Improper design, configuration or operation may result in
broadcast storm.
Redundant Ring in Danger
BR
5

6. Whitepaper www.korenix.com
• Link Restoration fixes a
Broken ring (Loop!)
• At the moment any
broadcast leads to a storm
• RM cannot detect the loop
and cannot block its path
because of the storm
R
Broken
R R
1. Link Restoration
When Broadcast Storm Happens To Redundant Ring
2. Network Restart 3. RM Malfunction
• Devices’ boot time varies
• Before RM starts to function,
topology loop and broadcast
storm will occur
• RM cannot detect the loop
and cannot block its path
because of the storm
• RM is the only manager of
the ring
• An occasional malfunction,
system halt or unexpected
problem may lead to a loop
and broadcast storm
6

7. Whitepaper www.korenix.com
Rate limiting constrains broadcast traffic at a
specified level and drops broadcast packets
(either good or bad) once the level is
exceeded, thus preventing further network
outages.
One LAN refers to one single broadcast domain.
Dividing a single network into smaller LANs by
layer 3 switches protects one another from
storm attacks. This, however, is a costly
solution to the problem.
1. Rate Limit 2. Dividing the Broadcast Domain
7
LAN2 LAN3LAN1
L3
Others: Mitigating Broadcast Storm
Mitigating is not the solution to root cause. It reduces the problem, but it does not stop the
storm. Duplicated broadcast packets still disturb the system’s normal operation.
100%
10%

8. Whitepaper www.korenix.com
1. Prevention within a Ring
Korenix’s Comprehensive Solution
8
Compared to other redundant ring technologies, korenix patented Seamless Restoration solves
the two root causes, link restoration and network restart, by preventing the network from
having loop topology at the first moment when a link is restored to a ring.
• Packet loss
• Topology change
during link restoration or
network restart
• Broadcast storm
due to loop topology when
a link restoration occurs or
a network is restarted
Seamless Restoration
• No broadcast storm
• No packet loss
• No topology change

9. Whitepaper www.korenix.com
Korenix’s Comprehensive Solution
2. Resilience to RM Failure
9
Korenix patented RM Redundancy technology is designed
to solve the single critical point problem of RM.
• When the RM fails or stops sending control packets, a
backup RM is activated, which operates automatically
without any manual configuration.
• It is not primary/secondary but fully redundant. Any
number of RM failures/malfunctions can be recovered
instantly.
The ring is always under control to prevent broadcast storm.
R
R
R
R
R
R
R
R

10. Whitepaper www.korenix.com
3. Protection beyond the Ring
Korenix’s Comprehensive Solution
10
With korenix patented Loop Protection (pending) enabled, a switch becomes a Protector and
starts to detect if there is any loop in the network. The connection between the protector and
the loop will be disabled if a loop is found. It can:
a) provide a double insurance on a ring in addition to RM redundancy
b) protect different parts of a LAN from each other by a korenix layer 2 switch instead of a
costly layer 3 switch
c) add korenix ring to pre-existing third party network and protect the ring from broadcast
storm
Rings in a LAN share the same broadcast domain
L2
KBroadcast
Storm
P
P
P
Broadcast
Storm

11. Whitepaper www.korenix.com
Email sales@korenix.com
Web www.korenix.com
Phone +886-2-8911-1000
Fax +886-2-2912-3328
Address F2, No. 188, Pao-Chiao
Rd. Shing-Tien City,
Taipei 23145, Taiwan
A broadcast storm occurs to industrial Ethernet
networks, and more typically in those, which
offer a ring for network redundancy. A ring is
exposed to the risk because of its loop
topology which is the root cause of broadcast
storm. Traditional treatment can only mitigate
the problem by rate limit or dividing broadcast
domain through layer 3 switches. However,
either ways does not aim at the root causes
and cannot stop the system being affected.
By offering comprehensive solutions that
include prevention, resilience and protection,
Korenix makes a contribution to the industrial
Ethernet world by enabling users to have a
reliable network free from broadcast storm.
Summary
11