fundamentals of a good ethernet infrastructure – stop chasing ghosts in your network!

Copyright © 2014 Rockwell Automation, Inc. All Rights Reserved.

PUBLIC INFORMATION

Fundamentals of a Good Ethernet Infrastructure Stop Chasing Ghosts in your Network!


Finding the Right Solution

2

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


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

4

What is Spanning Tree?

This is how the switches are physical connected



Spanning Tree blocks a port in the loop

5

What is Spanning Tree?

This is how the switches are logically connected

X



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?



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

7

What happens if the topology changes?

THIS PROCESS TAKES TIME!



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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


Filtered H2O 100.2.198.5 RSTP No HP ProCurve

J4813A -

2524 F.05.72

347


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



9

How do topology changes accidentally occur?



10

What are the potential consequences on the production network?

Let’s take a look and find out!



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Demo 1 Network

X



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

12

What is Rapid Spanning Tree?



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



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

14

What is Portfast?

Key Topic: Understanding the correct protocols and configurations is vital to having a high availability network


Agenda






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

16

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


Unmanaged Mishap

17

How do loops occur?


Unmanaged Mishap

18

Network Drawing?


Unmanaged Mishap

19

Demo 2 Network


Unmanaged Mishap

20

…but I thought loops were bad?


Unmanaged Mishap

21

What happens if we plug in a computer?


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


Agenda






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)


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)


Querier Chaos

26

Demo 3 Network

Multicast data is being produced and consumed by each controller

Controller 1


Agenda






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


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

29

A Client/Server Communication Problem


Caveat Conundrums

30

Demo 4 Network


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fundamentals of a good ethernet infrastructure – stop chasing ghosts in your network!

Technology

rockwell automation

convergence catastrophe

network root switch

production network

network x

complete network topology

network devices

hp procurve j4813a