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Fundamentals of a Good Ethernet Infrastructure Stop Chasing Ghosts in your Network!
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved.
Finding the Right Solution
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You have 3 identical pill bottles. No distinction can be made between the pills inside. Each bottle contains 100 pills. One bottle contains pills weighing 100 mg each, in another 99 mg each, and the other 98 mg each. You may only use the scale, only once. Determine which pills are in which bottle. Hint: You are allowed to remove the pills from the bottle.
Pill Bottle 1 Pill Bottle 2 Pill Bottle 3 Scale
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. 3
Agenda
Demo 3: Querier Chaos
Demo 4: A Caveat Conundrum
Demo 2: Unmanaged Mishap
Demo 1: Convergence Catastrophe
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved.
Convergence Catastrophe
IEEE 802.1D
Layer 2 protocol that runs on bridges and switches that support 802.1D
Prevents loops when redundant paths exist in a network
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What is Spanning Tree?
This is how the switches are physical connected
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved.
Convergence Catastrophe
Spanning Tree blocks a port in the loop
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What is Spanning Tree?
This is how the switches are logically connected
X
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved.
Convergence Catastrophe
A Root Switch is elected for each broadcast domain on the network
All switches exchange Bridge Protocol Data Units (BPDUs)
Each switches Root ID is advertised in this exchange
The lowest Root ID becomes the Root Switch
The Root Switch detects redundant paths
The optimum path is placed in a forwarding state
Non-optimum path(s) are placed in a blocked state
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How does this occur?
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved.
Convergence Catastrophe
Spanning Tree reconfigures the network
Root Switch recalculates path optimization
Paths may be rerouted
Network reconfiguration can occur when:
A redundant link in a forwarding state becomes unavailable
If network devices are added to the network
If additional paths are added on the network
Changing Port Speed/Duplex
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What happens if the topology changes?
THIS PROCESS TAKES TIME!
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved.
Convergence Catastrophe
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Example of topology changes on a production network
Name IP Address
Spanning-
Tree Root? Vendor
Model
Version
Up
Time
Topology
Changes
Last
Topology
Change /
Interval
Industrial Conc 100.2.198.3 RSTP
No HP ProCurve
J4812A -
2512 F.05.72
419
days 4,523,772 Every 0 secs
ScaleHouseRock 100.2.198.4 RSTP No HP ProCurve
J4813A -
2524 F.05.72
235
days 4,421,479 Every 0 secs
Filtered H2O 100.2.198.5 RSTP No HP ProCurve
J4813A -
2524 F.05.72
347
days 4,026,896 Every 0 secs
BinControls 100.2.198.6 RSTP No HP ProCurve
J4813A -
2524 F.05.72 62 days 4,397,673 Every 0 secs
GatewaySwitch2 100.2.198.20 STP No HP ProCurve 8000M C.09.30 3 days 54,050 Every 15 secs
Fruit Rec 100.2.198.21 STP Yes HP ProCurve 4000M C.09.30 3 days 5,062 Every 30 secs
Central Process 100.2.198.22 STP No HP ProCurve 4000M C.09.30 3 days 12,940 Every 30 secs
Finishing 100.2.198.23 STP No HP ProCurve 4000M C.09.30 3 days 15,890 26 hours
Gateway2A 100.2.198.26 RSTP No HP ProCurve
J4813A -
2524 F.05.72 19 days 1,106,872 Every 0 secs
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved.
Convergence Catastrophe
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How do topology changes accidentally occur?
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved.
Convergence Catastrophe
10
What are the potential consequences on the production network?
Let’s take a look and find out!
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved.
Convergence Catastrophe
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Demo 1 Network
X
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved.
Convergence Catastrophe
IEEE 802.1w
Layer 2 protocol that runs on bridges and switches that support 802.1D
Prevents loops when redundant paths exist in a network
The 5 different port states of Spanning Tree
Disabled
Listening
Learning
Blocking
Forwarding
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What is Rapid Spanning Tree?
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved.
Convergence Catastrophe
Does not utilize a lengthy convergence timer
The complete network topology converges in the time it takes for the
BPDU packets to travel through the network
How does this occur?
13
What is Rapid Spanning Tree?
This process may complete within a few 100 milliseconds
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved.
Convergence Catastrophe
For use with device ports only
Skips the listening and learning stage and immediately begins forwarding
Does not create topology change when the uplink toggles
Let’s observe Demo 1 again utilizing:
Rapid Spanning Tree Protocol
Portfast on the device ports
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What is Portfast?
Key Topic: Understanding the correct protocols and configurations is vital to having a high availability network
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. 15
Agenda
Demo 3: Querier Chaos
Demo 4: A Caveat Conundrum
Demo 2: Unmanaged Mishap
Demo 1: Convergence Catastrophe
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved.
Unmanaged Mishap
Unmanaged switches are utilized heavily on industrial networks
Unmanaged switches do not support loop protection or ring protocols
Unmanaged switches do not allow for a redundant network
Should not be used when a high availability architecture is required
Can be used on small, non-critical networks
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Plug „n Play
The Extension, A Technical Supplement to Control Network, Volume 6 Issue 1
“Managed switches are just Unmanaged switches with SNMP.”
Key Topic: Understand the application requirements, and employ the correct technology
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved.
Unmanaged Mishap
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How do loops occur?
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved.
Unmanaged Mishap
18
Network Drawing?
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved.
Unmanaged Mishap
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Demo 2 Network
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved.
Unmanaged Mishap
20
…but I thought loops were bad?
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved.
Unmanaged Mishap
21
What happens if we plug in a computer?
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved.
Unmanaged Mishap
SLC™ 500s send ARP every 1,192 seconds
Ethernet/IP communication modules send ARP every 45 seconds
Different vendor communication protocols may not send ARPs at other
intervals, or not at all
Implications on an unmanaged loop:
It only takes one broadcast message to shut down the network
Engineer may leave site before problem occurs
Problem may go unnoticed for months
Issue may be difficult to locate
22
Industrial Ethernet Communication Protocols
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved. 23
Agenda
Demo 3: Querier Chaos
Demo 4: A Caveat Conundrum
Demo 2: Unmanaged Mishap
Demo 1: Convergence Catastrophe
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved.
Querier Chaos
Manages the efficient delivery of multicast traffic
IGMP allows the network to understand which endpoints are interested in
which multicast data
Protocol is available in virtually all managed switches, “smart” switches,
and the 1783-ETAP
Layer-2 Access Switches should be configured to
perform IGMP Snooping
Layer-3 Distribution Switch should be configured to
perform the IGMP Querier function
24
Internet Group Management Protocol (IGMP)
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved.
Querier Chaos
Ethernet/IP devices support IGMP version 2
Many other network devices support IGMP version 1
In IGMP version 1, after a host fails to respond to three queries, it is dropped from a multicast group
In IGMP version 2, hosts can also actively leave a multicast group
It is recommended for all devices to be IGMP version 2 on an Ethernet/IP
If more than one switch is configured to be IGMP Querier, the switch or router with the lowest IP address will take this role
What happens when you mix IGMP versions and different switch vendors?
25
Internet Group Management Protocol (IGMP)
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved.
Querier Chaos
26
Demo 3 Network
Multicast data is being produced and consumed by each controller
Controller 1
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Agenda
Demo 3: Querier Chaos
Demo 4: A Caveat Conundrum
Demo 2: Unmanaged Mishap
Demo 1: Convergence Catastrophe
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved.
Caveat Conundrums
Certain IOS versions may have known anomalies
It is important that any IOS version, currently being utilized, or being
upgraded to, is properly researched for bugs
IOS anomalies may cause applications to not perform at all, perform
intermittently, or only perform with certain switch configurations
An application that is working correctly can be “broken” by upgrading
an IOS
A situation was recently discovered at a customer site, which exemplifies
an IOS anomaly
28
The important of “Bug Scrubbing” IOS versions
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved.
Caveat Conundrums
What was discovered:
If the Client and Server are in the same subnet, the communication
works
If the Client and Server are in different subnets (routed), the
communication does not work
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A Client/Server Communication Problem
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved.
Caveat Conundrums
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Demo 4 Network
Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved.
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