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

2. Before Switching

3. Network with Switching

4. 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
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. Both Bridges and Switches
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
dccb.d74b DYNAMIC Fa0/1
1 000a.f467.9e80 DYNAMIC Fa0/3
1 000a.f467.9e8b DYNAMIC Fa0/4
1 000a.f467.9e8c DYNAMIC Fa0/3
b7f.c2b0 DYNAMIC Fa0/3
dc.460b DYNAMIC Fa0/3
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. Host_1 sends a unicast frame to Router C
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
1900A(config)#ip default-gateway
1900A(config)#banner
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
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
2950B(config-if)#no shut
2950B(config-if)#exit
2950B(config)#ip default-gateway
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
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to , 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)
Port
Cost
BID
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#show spanning-tree vlan 2
Switch#sh spanning-tree
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority
Address cc0
Cost
Port (GigabitEthernet0/1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority (priority sys-id-ext 1)
Address b.6880
Aging Time 300
Interface Role Sts Cost Prio.Nbr Type
Fa0/ Altn BLK P2p
Gi0/ Root FWD P2p
Switch#show spanning-tree vlan 2

29. 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

30. 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

31. BPDUGuard BPDUFilter 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

32. Use it on switches that have blocked port
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

33. Use it on all switches 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

34. 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

35. 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 = 0x Pseudo port-channel = Po1
Port index = 0 Load = 0x00 Protocol = PAgP
[output cut]

36. Selecting Root Bridge Switch(config)#spanning-tree vlan 1 priority ?
< > 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