Configuring Catalyst Switch Operations

Identifying Problems That Occur in
Redundant Switched Topologies

© 2006 Cisco Sys...
Outline
• Overview
• Redundant Switched and Bridged Topologies
• Broadcast Storms
• Multiple Frame Transmissions
• MAC Dat...
Redundant Topology

• Redundant topology eliminates single points of failure.
• Redundant topology causes broadcast storms...
Broadcast Storms

• Host X sends a broadcast.
• Switches continue to propagate broadcast traffic
over and over.
© 2006 Cis...
Multiple Frame Copies

• Host X sends a unicast frame to router Y.
• The MAC address of router Y has not been learned by
e...
MAC Database Instability

•
•
•
•
•

Host X sends a unicast frame to router Y.
The MAC address of router Y has not been le...
Summary
• Bridged and switched networks are commonly designed with
redundant links and devices, which can introduce proble...
© 2006 Cisco Systems, Inc. All rights reserved.

ICND v2.3—1-8
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Icnd23 s01l02

  1. 1. Configuring Catalyst Switch Operations Identifying Problems That Occur in Redundant Switched Topologies © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—1-1
  2. 2. Outline • Overview • Redundant Switched and Bridged Topologies • Broadcast Storms • Multiple Frame Transmissions • MAC Database Instability • Summary © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—1-2
  3. 3. Redundant Topology • Redundant topology eliminates single points of failure. • Redundant topology causes broadcast storms, multiple frame copies, and MAC address table instability problems. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—1-3
  4. 4. Broadcast Storms • Host X sends a broadcast. • Switches continue to propagate broadcast traffic over and over. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—1-4
  5. 5. Multiple Frame Copies • Host X sends a unicast frame to router Y. • The MAC address of router Y has not been learned by either switch. • Router Y will receive two copies of the same frame. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—1-5
  6. 6. MAC Database Instability • • • • • Host X sends a unicast frame to router Y. The MAC address of router Y has not been learned by either switch. Switches A and B learn the MAC address of host X on port 0. The frame to router Y is flooded. Switches A and B incorrectly learn the MAC address of host X on port 1. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—1-6
  7. 7. Summary • Bridged and switched networks are commonly designed with redundant links and devices, which can introduce problems such as broadcast storms, multiple frame transmission, and MAC database instability. • A broadcast storm is created when each switch on a redundant network floods broadcast frames endlessly. • Multiple frame transmissions occur when multiple copies of the same frame arrive at the intended host, potentially causing problems with the receiving protocol. • MAC database instability occurs when multiple copies of a frame arrive on different ports of a switch. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—1-7
  8. 8. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—1-8

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