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Chapter 8 Layer 2 Switching and Spanning Tree Protocol (STP)

Chapter 8 Layer 2 Switching and Spanning Tree Protocol (STP). Before Switching. Network with Switching. Switching Service. Layer 2 switches provides the following: Hardware- based bridging (ASIC) Switch uses ASIC in building and maintaining their Forward/Filter table. Wire speed

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Chapter 8 Layer 2 Switching and Spanning Tree Protocol (STP)

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  1. Chapter 8Layer 2 Switching and Spanning Tree Protocol (STP)

  2. Before Switching

  3. Network with Switching

  4. SwitchingService Layer 2 switches provides the following: • Hardware- based bridging (ASIC) Switch uses ASIC in building and maintaining their Forward/Filter table. • Wire speed Switch create a private dedicated Collision Domain (for each port) and provide independent bandwidth on each port so increase the bandwidth for each user (unlike Hub). • Low latency Switches and bridges are faster than Routers because they do not look at network layer header information. • Low cost

  5. Bridges vs.Switches • Bridges are software base , while switches are hardware base because they use (ASIC). • A switch can be viewed as multi port bridge. • Switches have higher number of ports than bridges. • Bridge can have only one spanning tree , while switches can have many. • Both Bridges and Switches • Forward layer 2 broadcast. • Learn MAC address by examining the source address of each frame received. • Make forward decision based on layer 2 address. • Break up collision domain but still have a single broadcast domain (Switches have 1 broadcast domain BY DEFAULT).

  6. Three switch functions at layer 2 • Address Learning • Forward / Filter decision • Loop avoidance

  7. Address Learning. Notice that a switch or a bridge never learns a BROADCAST or MULTICAST address because broadcast or multicast never appear as the source address of the frame.

  8. Address Learning. • Switch#sh mac address-table • Vlan Mac Address Type Ports • ---- ----------- -------- ----- • 1 0005.dccb.d74b DYNAMIC Fa0/1 • 1000a.f467.9e80 DYNAMIC Fa0/3 • 1 000a.f467.9e8b DYNAMIC Fa0/4 • 1 000a.f467.9e8c DYNAMIC Fa0/3 • 1 0010.7b7f.c2b0 DYNAMIC Fa0/3 • 1 0030.80dc.460b DYNAMIC Fa0/3 • 1 0030.9492.a5dd DYNAMIC Fa0/1 • 00d0.58ad.05f4 DYNAMIC Fa0/1 • Total Mac Addresses for this criterion: 8 • Switch(config)#mac-address-table static aaaa.bbbb.cccc vlan 1 int fa0/5

  9. Redundant link between Switches Problems 1.Broadcast Storm

  10. 2. Multiple frame copies

  11. 3. Instable MAC Table • Host_1 sends a unicast frame to Router C • The MAC address of Router C has not been learned by either switch. • Switches A and B learn the MAC address of Host_1 on port 0. • The frame to Router C is flooded. • Switches A and B incorrectly learn the MAC address of Host_1on port 1.

  12. Switching Modes • Store and Forward. • Cut through (Fast forward ,Real time, Wire speed). • Fragment free (Modified Cut through)

  13. CISCO 1900 Switch Configuration >enable #config t (config)#enable password level 1 cisco (config)#enable password level 15 cisco1 (config)#enable secret cisco (config)#hostname 1900A 1900A(config)#ip address 192.168.10.51 255.255.255.0 1900A(config)#ip default-gateway 192.168.10.1 1900A(config)#banner motd @ This is 1900A Switch @ 1900A(config)#int fa0/12 1900A(config)#description Connection_to_HR 1900A(config)#^Z 1900A#sh ip 1900A#delete nvram

  14. CISCO 2950 Switch Configuration Switch>en Switch#config t Enter configuration commands, one per line. End with CNTL/Z. Switch(config)#hostname 2950B 2950B(config)#enable secret cisco 2950B(config)#line console 0 2950B(config-line)#password cisco 2950B(config-line)#login 2950B(config)#line vty 0 15 2950B(config-line)#password telnet 2950B(config-line)#banner motd @ Enter the text followed by the '@' to finish This is 2950B Switch @ 2950B(config)#int f0/4 2950B(config-if)#desc connection to 2950C 2950B(config-if)#int f0/5 2950B(config-if)#desc 2nd connection to 2950C 2950B(config-if)#int vlan 1 2950B(config-if)#ip address 192.168.20.51 255.255.255.0 2950B(config-if)#no shut 2950B(config-if)#exit 2950B(config)#ip default-gateway 192.168.20.1 2950B(config)#exit 2950B#copy run start Destination filename [startup-config]? (enter) Building configuration... [OK]

  15. CISCO 2950 Switch Configuration 2950B#erase startup 2950B#delete flash:nvram 2950B#reload 2950B#ping 192.168.30.17 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 192.168.30.17, timeout is 2 seconds: .!!!! Success rate is 80 percent (4/5), round-trip min/avg/max = 1/1/1 ms

  16. Port Security Switch#config t Switch(config)#int f0/1 Switch(config-if)#switchport port-security ? aging Port-security aging commands mac-address Secure mac address maximum Max secure addresses violation Security violation mode <cr> Switch(config-if)#switchport port-security maximum 1 Switch(config-if)# switchport port-security violation ? protect Security violation protect mode restrict Security violation restrict mode shutdown Security violation shutdown mode Switch(config-if)#switchport port-security violation shutdown

  17. Port Security Switch(config-if)#switchport port-security mac-address sticky Switch(config-if)#switchport port-security maximum 2 Switch(config-if)#switchport port-security violation shutdown

  18. Spanning Tree Protocol

  19. Bridge Protocol Data Unit (BPDU) • BID: Priority, MAC Address. • Cost: • B.W Cost • 10Gbps 2 • 1Gbps 4 • 100Mbps 19 • 10Mbps 100 • Port: Priority, Port no. • Cost • BID • Port Priority • Port No.

  20. STP Example 1

  21. STP Example 2

  22. STP Example 3

  23. STP Example 4

  24. STP Example 5

  25. STP Example 6

  26. STP Example 7

  27. Switch#sh spanning-tree VLAN0001 Spanning tree enabled protocol ieee Root ID Priority 32769 Address 0012.8061.0cc0 Cost 8 Port 25 (GigabitEthernet0/1) Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 32769 (priority 32768 sys-id-ext 1) Address 0012.806b.6880 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 300 Interface Role Sts Cost Prio.Nbr Type ---------------- ---- --- --------- -------- -------------------------------- Fa0/16 Altn BLK 19 128.16 P2p Gi0/1 Root FWD 4 128.25 P2p Switch#show spanning-tree vlan 2

  28. Configuring Catalyst Switches • Administrative functions (General settings) • Configuring the IP address and subnet mask • Setting the IP default gateway • Setting port security • Setting PortFast • Enabling BPDUGuard and BPDUFilter • Enabling UplinkFast • Enabling BackboneFast • Enabling RSTP (802.1w) • Enabling EtherChannel • Configuring an STP root switch • Using the CNA to configure a switch

  29. Spanning Tree PortFast Switch(config-if)#spanning-tree portfast ? disable Disable portfast for this interface trunk Enable portfast on the interface even in trunk mode <cr> Switch(config-if)#exit Switch(config)#int range fastEthernet 0/1 - 12 Switch(config-if-range)#spanning-tree portfast

  30. BPDUGuard Switch(config-if-range)#spanning-tree bpduguard ? disable Disable BPDU guard for this interface enable Enable BPDU guard for this interface Switch(config-if-range)#spanning-tree bpduguard enable BPDUFilter Switch(config-if-range)#spanning-tree bpdufilter ? disable Disable BPDU filtering for this interface enable Enable BPDU filtering for this interface Switch(config-if-range)#spanning-tree bpdufilter enable

  31. UPLinkFast Switch(config)#spanning-tree uplinkfast Switch(config)#do show spanning-tree uplinkfast UplinkFast is enabled Station update rate set to 150 packets/sec. UplinkFast statistics ----------------------- Number of transitions via uplinkFast (all VLANs) : 1 Number of proxy multicast addresses transmitted (all VLANs) : 8 Name Interface List -------------------- ------------------------------------ VLAN0001 Fa0/1(fwd), Fa0/2 Use it on switches that have blocked port

  32. BackboneFast Switch(config)#spanning-tree backbonefast Switch(config)#do show spanning-tree backbonefast BackboneFast is enabled BackboneFast statistics ----------------------- Number of transition via backboneFast (all VLANs) : 0 Number of inferior BPDUs received (all VLANs) : 2 Number of RLQ request PDUs received (all VLANs) : 0 Number of RLQ response PDUs received (all VLANs) : 1 Number of RLQ request PDUs sent (all VLANs) : 1 Number of RLQ response PDUs sent (all VLANs) : 0 Use it on all switches

  33. STP (802.1d) x RapidSTP (802.1w) Switch(config)#spanning-tree mode ? mst Multiple spanning tree mode pvst Per-Vlan spanning tree mode rapid-pvst Per-Vlan rapid spanning tree mode Switch(config)#spanning-tree mode rapid-pvst

  34. EtherChannel Switch(config)#int port-channel 1 Switch(config-if)#int range f0/1-2 Switch(config-if-range)#switchport mode trunk 1d03h: %SPANTREE_FAST-7-PORT_FWD_UPLINK: VLAN0001 FastEthernet0/2 moved to Forwarding (UplinkFast). Switch(config-if-range)#switchport nonegotiate Switch(config-if-range)#channel-group 1 mode desirable Switch(config-if-range)#do sh int fa0/1 etherchannel Port state = Up Sngl-port-Bndl Mstr Not-in-Bndl Channel group = 1 Mode = Desirable-Sl Gcchange = 0 Port-channel = null GC = 0x00010001 Pseudo port-channel = Po1 Port index = 0 Load = 0x00 Protocol = PAgP [output cut]

  35. Selecting Root Bridge Switch(config)#spanning-tree vlan 1 priority ? <0-61440> bridge priority in increments of 4096 Switch(config)#spanning-tree vlan 1 root ? primary Configure this switch as primary root for this spanning tree secondary Configure switch as secondary root Switch(config)#spanning-tree vlan 1 root primary

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