CNNA3-Chapter 5 pptx

CCNA3-1 Chapter 5-1 Chapter 5Chapter 5 Spanning Tree ProtocolSpanning Tree Protocol (STP) (STP) Part IPart I CCNA3-2 Chapter 5-1 Spanning Tree Protocol (STP)Spanning Tree Protocol (STP) Redundant Layer 2 TopologiesRedundant Layer 2 Topologies CCNA3-3 Chapter 5-1 Redundant Layer 2 TopologiesRedundant Layer 2 Topologies •• As businesses become increasingly dependent on the As businesses become increasingly dependent on the network, the availability of the network infrastructure network, the availability of the network infrastructure becomes a critical business concern. becomes a critical business concern. •• RedundancyRedundancy is the solution for achieving the necessary is the solution for achieving the necessary availability.availability. •• Layer 2 redundancy improves the availability of the Layer 2 redundancy improves the availability of the network by implementing network by implementing alternate network pathsalternate network paths by by adding equipment and cabling.adding equipment and cabling. •• Having multiple paths for data to traverse the network Having multiple paths for data to traverse the network allows for a single path to be disruptedallows for a single path to be disrupted without impacting without impacting the connectivity of devices on the network. the connectivity of devices on the network. CCNA3-4 Chapter 5-1 RedundancyRedundancy CCNA3-5 Chapter 5-1 RedundancyRedundancy Redundant paths create Redundant paths create loops loops in the network.in the network. How are they controlled?How are they controlled? Spanning Tree ProtocolSpanning Tree Protocol CCNA3-6 Chapter 5-1 RedundancyRedundancy •• The Spanning Tree Protocol The Spanning Tree Protocol (STP)(STP) is enabled on all is enabled on all switches.switches. •• STP has placed some switch ports in STP has placed some switch ports in forwardingforwarding state and state and other switch ports in other switch ports in blockingblocking state.state. ForwardForward BlockedBlocked CCNA3-7 Chapter 5-1 Issues with RedundancyIssues with Redundancy •• RedundancyRedundancy is an important part of the hierarchical design.is an important part of the hierarchical design. •• When multiple paths exist between two devices on the When multiple paths exist between two devices on the network and network and STP has been disabledSTP has been disabled on those switches, a on those switches, a Layer 2 loopLayer 2 loop can occur.can occur. •• If If STP is enabledSTP is enabled on these switches, on these switches, which is the defaultwhich is the default, , a a Layer 2 loop would not occurLayer 2 loop would not occur CCNA3-8 Chapter 5-1 Issues with RedundancyIssues with Redundancy •• Ethernet frames do not have a Ethernet frames do not have a TimeTime ToTo Live (TTL)Live (TTL) parameter parameter like IP packets.like IP packets. •• As a result, if they are not terminated properly on a As a result, if they are not terminated properly on a switched network, they continue to bounce from switch to switched network, they continue to bounce from switch to switch endlessly.switch endlessly. CCNA3-9 Chapter 5-1 Issues with RedundancyIssues with Redundancy •• Remember that switches use the Remember that switches use the Source MAC addressSource MAC address to to learn where the devices are and learn where the devices are and enters this informationenters this information into into their MAC address tables.their MAC address tables. •• Switches will Switches will flood the frames for unknown destinationsflood the frames for unknown destinations until until they learn the MAC addresses of the devices. they learn the MAC addresses of the devices. CCNA3-10 Chapter 5-1 Issues with RedundancyIssues with Redundancy •• Additionally, Additionally, multicasts and broadcastsmulticasts and broadcasts are also flooded out are also flooded out all ports except the receiving port. all ports except the receiving port. (Multicasts will not be (Multicasts will not be flooded if the switch has been specifically configured to flooded if the switch has been specifically configured to handle multicasts.) handle multicasts.) [...]... remaining ports CCNA3-13 Chapter 5- 1 RealReal-World Redundancy Issues • Loops in the Wiring Closet: • Usually caused by an error in cabling CCNA3-14 Chapter 5- 1 RealReal-World Redundancy Issues • Loops in Cubicles: • Some users have a personal switch or hub Affects all of the traffic on S1 CCNA3- 15 Chapter 5- 1 Spanning Tree Protocol (STP) Introduction to STP CCNA3-16 Chapter 5- 1 Introduction to STP • Redundancy:... switch(configswitch(config-if)#end CCNA3- 25 Chapter 5- 1 Best Path • Verifying the port and path cost cost Port Cost Path Cost CCNA3-26 Chapter 5- 1 STP Bridge Protocol Data Unit • STP determines a root bridge for the spanning-tree instance spanningby exchanging Bridge Protocol Data Units (BPDU) (BPDU) Identifies the root bridge and the cost of the path to the root bridge CCNA3-27 Chapter 5- 1 STP Bridge Protocol Data... CCNA3-28 Chapter 5- 1 BPDU Process • Root Bridge Election Process: S3 believes S2 is the root bridge S1 still thinks it is the root bridge CCNA3-29 Chapter 5- 1 BPDU Process • Root Bridge Election Process: S2 and S1 both think that they are the root bridge CCNA3-30 Chapter 5- 1 BPDU Process • Root Bridge Election Process: S3 recognizes S1 as the root S2 recognizes S1 as the root CCNA3-31 Chapter 5- 1 BPDU Process... Root Bridge Election Process: If the root bridge fails, the election process begins again CCNA3-32 Chapter 5- 1 Bridge ID Early STP implementation – no VLANs That means that there is a separate instance of STP for each VLAN CCNA3-33 Changed to include VLAN ID Chapter 5- 1 Bridge ID CCNA3-34 Chapter 5- 1 Bridge ID • Bridge Priority: • A customizable value that you can use to influence which switch becomes... priority CCNA3- 35 Chapter 5- 1 Bridge ID • Bridge Priority: • Notice that the addition of the VLAN ID leaves fewer bits available for the bridge priority (4 instead of 16) • As a result, the bridge priority is assigned in multiples of 4096 4096 • The priority is added to the extended system value (VLAN ID) to uniquely identify the priority and VLAN of the BPDU frame + CCNA3-36 Chapter 5- 1 ... CCNA3-11 Chapter 5- 1 Issues with Redundancy • Broadcast Storms: In fact, the entire network can no longer process new traffic and comes to a screeching halt CCNA3-12 Because of the high level STP so a it a PC3 sendsPC4 sendsaa and PC1PC2 sends No broadcast a of traffic, sends Another loop cannotbroadcastloop createsloopbebroadcast yet another broadcast is processed created Chapter 5- 1 Issues with Redundancy... paths CCNA3-17 Chapter 5- 1 SpanningSpanning-Tree Algorithm (STA) • STP Topology – Avoiding a loop: loop: S1 forwards a andin STP is in use is S3 S2 forwards the Because F0/2 PC1 sends the broadcast –portthe has placed but F0/2 blocking state, broadcast broadcast state, in not to S3.state to broadcast is not blocking S3 forwarded back to avoid a loop S2 – NO LOOP! CCNA3-18 Chapter 5- 1 SpanningSpanning-Tree... frames with the lower root ID to the other adjacent switches • Eventually, the switch with the lowest BID ends up being identified as the root bridge for the spanning-tree spanninginstance CCNA3-23 Chapter 5- 1 Best Path • Now that the root bridge has been elected, the STA starts the process of determining the best paths to the root bridge from all destinations in the broadcast domain • The path information... destination to the root bridge • The default port costs are specified by the IEEE and defined by the speed at which the port operates Link Speed Cost 10Gbps 1Gbps 4 100Mbps 19 10Mbps CCNA3-24 2 100 Chapter 5- 1 Best Path • You are not restricted to the defaults defaults • The cost of a path can be manually configured to specify that a specific path is the preferred path instead of allowing the STA to choose... Failure: Failure: S3 port activated S3 port back to S3 and S1 forward S2 forwards a PC1 Sends the blocking mode mode broadcast the broadcast broadcast CCNA3-19 Trunk 1 Failure Trunk 1 comes back up Chapter 5- 1 SpanningSpanning-Tree Algorithm (STA) • Terminology: • Root Bridge: • A single switch used as the reference point for all calculations • Root Ports: • The switch port closest to the root bridge • Designated . CCNA3-1 Chapter 5- 1 Chapter 5Chapter 5 Spanning Tree ProtocolSpanning Tree Protocol (STP) (STP) Part IPart I CCNA3-2 Chapter 5- 1 Spanning Tree Protocol. connectivity of devices on the network. CCNA3-4 Chapter 5- 1 RedundancyRedundancy CCNA3 -5 Chapter 5- 1 RedundancyRedundancy Redundant paths create Redundant