TDC363-5-stp - TDC 363\/413 Introduction to LANs Switched LAN Redundancy Greg Brewster DePaul University TDC 363 Greg Brewster DePaul University 1 Topics

TDC363-5-stp - TDC 363/413 Introduction to LANs Switched...

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TDC 363/413Introduction to LANsGreg BrewsterDePaul UniversitySwitched LAN RedundancyTDC 363Greg Brewster, DePaul University1
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Providing Redundancy in Switched LANsSpanning Tree Protocol (STP)EtherChannelRapid Spanning Tree Protocol (RSTP)Per-VLAN Rapid Spanning Tree (PVRST+)Configuration and Load Balancing Controlling the RootTopicsTDC 363Greg Brewster, DePaul University2
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Providing RedundancyIn a LAN design, you want to ensure that traffic can always flow even if switches or links fail.This requires redundant pathsThis also creates the potential for loopsA switched network can’t have loopsA solution for basic parallel backup links is LinkAggregation (EtherChannel)A general solution for loops in switched environments is Spanning Tree ProtocolProvides logically loop-free environmentTDC 363Greg Brewster, DePaul University3
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The need for spanning trees:Parallel switched paths for redundancy possible loopingTDC 363Greg Brewster, DePaul University4
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A LoopTDC 363Greg Brewster, DePaul University5
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Presentation_ID6© 2008 Cisco Systems, Inc. All rights reserved.Cisco ConfidentialPurpose of Spanning TreeRedundancy at OSI Layers 1 and 2Multiple cabled paths between switches: Provide physical redundancy in a switched network.Improves the reliability and availability of the network.Enables users to access network resources, despite path disruption.But, without STP, Loops can cause these problems.
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Presentation_ID7© 2008 Cisco Systems, Inc. All rights reserved.Cisco ConfidentialPurpose of Spanning TreeIssues with Layer 1 Redundancy: MAC Database InstabilityEthernet frames do not have a time to live (TTL) attribute. Frames continue to propagate between switches endlessly, or until a link is disrupted and breaks the loop. Results in MAC database instability. Can occur due to broadcast frames forwarding. If there is more than one path for the frame to be forwarded out, an endless loop can result. When a loop occurs, it is possible for the MAC address table on a switch to constantly change with the updates from the broadcast frames, resulting in MAC database instability.(see example: CNA SN 2.1.1.2)
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Presentation_ID8© 2008 Cisco Systems, Inc. All rights reserved.Cisco ConfidentialPurpose of Spanning TreeIssues with Layer 1 Redundancy: Broadcast StormsA broadcast storm occurs when there are so many broadcast frames caught in a Layer 2 loop that all available bandwidth is consumed. It is also known as denial of serviceA broadcast storm is inevitable on a looped network. As more devices send broadcasts over the network, more traffic is caught within the loop; thus consuming more resources.
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