1. Cisco networking CNET-448
Chapter Introduction
Cisco networking CNET-448
Chapter 1
Enhanced Switched Technologies
Prepared by: Sikandar Shah

2. Objectives The ICND2 Topics Covered in this chapter include:
Chapter Introduction
Objectives
The ICND2 Topics Covered in this chapter include:
LAN Switching Technologies
VLAN overview
VTP
RSTP
PVSTP
Etherchannels
Configure and verify PVSTP operation
describe root bridge election
spanning tree mode
Troubleshooting
Troubleshoot and Resolve Spanning Tree operation issues
root switch
priority
port states
Troubleshoot etherchannel problems

3. VLAN OVERVIEW
VLAN Configuration
To configure VLANs on a Cisco Catalyst switch, use the global config vlan command.
S1(config)#vlan 2
S1(config-vlan)#name Sales
S1(config-vlan)#vlan 3
S1(config-vlan)#name Marketing
You can create VLANs from 1 to 4094.
Standard Vlans range 1 to 1005
VLAN 1, 1002, 1003,1004,1005 are reserved. VLAN 1 is called the native vlan.
Extended range VLANs can be created only in VTP transparent mode only.
Use command Show vlan and show vlan brief to display vlans.

4. VLAN Overview
Switchport Modes
Access: It puts the interface (access port) into permanent nontrunking mode and negotiates to convert the link into a nontrunk link.
Dyanmic Auto: The interface passively waits to receive a trunk negotiation message. It Will trunk to neighbor switch only if the remote port is set to trunk(on) or to desirable mode.
Dyamic Desirable: The interface actively attempt to convert the link to a trunk link. This will trunk with all port modes except access.
Nonegotiate: Prevents the interface from generating DTP frames, it is used when switchport mode is access or trunk.
Trunk (on): Puts the interface into permanent trunking mode and negotiates to convert the neighboring link into a trunk link.

5. VLAN Trunking Protocol (VTP)
VLAN OVERVIEW
VLAN Trunking Protocol (VTP)
VTP allows you to add, delete, and rename VLANs— information that is then propagated to all other switches in the VTP domain.
VLANs can be created on switch with VTP server mode only.
All servers that need to share VLAN information must use the same domain name.
A switch can share VTP domain information with other switches only if they’re configured into the same VTP domain.
VTP information is sent between switches only via a trunk port.

6. VLAN Trunking Protocol (VTP)
VLAN OVERVIEW
VLAN Trunking Protocol (VTP)

7. VLAN OVERVIEW
VTP Modes of Operation
Server : This is the default mode for all Catalyst switches. The switch must be in server mode to be able to create, add, and delete VLANs in a VTP domain. VLAN configurations are saved in NVRAM on the switch.
Client : In this mode switches receive information from VTP servers forward updates to other switches. VLAN information sent from a VTP server isn’t stored in NVRAM
Transparent: The switch must be in VTP transparent mode to let you create VLAN IDs from 1006 to 4094.

8. VLAN Trunking Protocol (VTP)
VLAN OVERVIEW
VLAN Trunking Protocol (VTP)

9. Spanning-Tree Protocol(STP)
The primary objectives of STP is to prevent network loops on layer 2 network bridges or switches.
STP monitors the network to track all links and shut down the redundant ones.
STP uses the spanning-tree algorithm (STA) to first create a topology Database and then search out and Disable Redundant links.
With STP running, frames will be forwarded on only premium, STP-chosen links.
The default IEEE version of STP is 802.1d.

10. A switched network with switching loops
Switching loops can cause broadcast storms, multiple frame copies, and MAC table thrashing!

11. Switch network with redundant Links
STP Working Mechanism
Switch network with redundant Links
A Switched network after convergence

12. Spanning Tree Terms STP Explanation
Root Bridge: Switch with the lowest bridge ID becomes the root bridge. It is the focal point in the network, all decision are made from root bridge perspective.
Bridge ID: It is used to keep track of all switches in the network. It is determined by a combination of the bridge priority and MAC address.
Non root Bridges: Non-root bridges exchange BPDUs with all bridges and update STP topology database.
Port Cost: The cost of a link is determined by its bandwidth.

13. Spanning Tree Terms STP Explanation
Path Cost: Path cost is the sum of the various port costs to the root bridge.
BPDU: These are data messages exchanged between the switches containing information about ports, costs, priorities and bridge ID.
Convergence: Convergence occurs when all ports on bridges and switches have transitioned to either forwarding Or blocking modes. No data will be forwarded until convergence is complete. The original STP (802.1d) takes 50 seconds to go from blocking to forwarding mode by default.

14. Spanning Tree algorithm
Bridge Port Roles
Root Port: The port with the best path to the root bridge is called the root port. Every non-root bridge must have a root port. All root ports are placed in forwarding state.
Designated Port: A designated port is one that’s been determined to have the best (lowest) cost to get to on a given network segment.
Non-designated Port: This is the link with highest cost and kept blocked.
Forwarding Port: It forwards frames and can be either a root port or a designated port.
Blocked Port: It can only receive BPDU frames from other switches.
Alternate port: This corresponds to the blocking state of d, and is a term used with the newer 802.1w (RSTP).
Backup Port: It is connected on a LAN segment with another port on that switch is acting the designated port.

15. Spanning Tree algorithm
Bridge Port Roles

16. Spanning-Tree Port States
IEEE 802.1d STP
Spanning-Tree Port States
Disabled: It is non-operational state.
Blocking : Port in this state will not forward frames, just listens to BPDUs.
Listening: A port in the listening state prepares to forward data frames without populating the MAC address table.
Learning: A port in learning state populates the MAC address table but still doesn’t forward data frames.
Forwarding: If the port is still a designated or root port at the end of the learning state, it enters the forwarding state.

17. Link costs for 802.1d Standard
IEEE 802.1d STP
Link costs for 802.1d Standard
Port cost is based on the speed of the link.
Link speed
Cost
10,000=10 Gb/s 2
1000 = 1 Gb/s 4
100 Mb/s 19
10 Mb/s
100

18. Root Bridge and Root Port determination # 1
STP operations
Root Bridge and Root Port determination # 1

19. Root Bridge and Root Port determination
STP operations
Root Bridge and Root Port determination
Which bridge is the root bridge? ________
The root port for SW-D. ________
The root port for SW-B _________
The root port for SW-A _________
Blocked Ports _________________
Designated Ports _______________

20. Root Bridge and Root Port determination # 2
STP operations
Root Bridge and Root Port determination # 2

21. RSTP Configuration commands
Sw(config) # spanning-tree mode rapid-pvst
SW# show spanning-tree
SW# show mac address-table

22. Types of Spanning-tree Protocols
STP Configuration
Types of Spanning-tree Protocols
IEEE 802.1d: The original standard for bridging and STP. It’s also referred to as Common Spanning Tree (CST).
PVST+ (Per VLAN Spanning Tree +): The Cisco proprietary enhancement for STP that provides a separate 802.1d spanning-tree instance for each VLAN. It can have multiple root bridges.
IEEE 802.1w: Also called Rapid Spanning Tree Protocol (RSTP), paved the way for much faster network convergence.
Rapid PVST+: Cisco’s version of RSTP that also uses PVST+ and provides a separate instance of 802.1w per VLAN.
802.1s (MSTP) : It is known as IEEE 802.ls. It reduces the number of required STP instances by allowing us to map multiple VLANs. It essentially allows us to create VLAN sets.

23. STP & RSTP Ports states comparison
802.1d & 802.1w
STP & RSTP Ports states comparison
802.1d state
802.1w state
Disabled
Discarding
Blocking
Listening
Learning
Forwarding

24. Spanning-tree Failure Consequences
STP Troubleshooting
Spanning-tree Failure Consequences
The list of the problems that will occur in a failed STP network.
The load on all links begins increasing and more and more frames enter the loop.
Traffic will increase on the switches because all the circling frames actually get duplicated.
The MAC address table is now completely unstable.
The device becomes unresponsive.

25. Network Optimization
PortFast
We can use PortFast on the ports on S1 to help them transition to the STP forwarding state immediately upon connecting to the switch.
ports will transition from blocking to forwarding state immediately.
S1(config)#spanning-tree portfast default
S1(config-if)#spanning-tree portfast

26. Network Optimization
BPDU Gaurd
BPDU Guard is used for switch ports for which PortFast is enabled. This is because if a switch port that has PortFast enabled receives a BPDU on that port, it will place the port into error disabled (shutdown) state.
S1(config)# spanning-tree portfast bpduguard default
On an interface:
S1(config-if)#spanning-tree bpduguard enable

27. EtherChannel (Port Channel)
Port Channelling
EtherChannel (Port Channel)
Etherchannel bundles together multiple links between switches by using port channelling. EtherChannel is Cisco’s proprietary term for port channelling. It groups several Fast Ethernet or Gigabit Ethernet ports into one logical channel.
Layer 2 STP and layer 3 routing protocols treat those bundled links as a single one.
There are two version of port channel negotiation protocols.
Port Aggregation Protocol (PAgP): Cisco’s proprietary protocol
Link Aggregation Control Protocol (LACP): IEEE 802.3ad standard protocol
Cisco EtherChannel allows us to bundle up to 8 FastEthernet or two gigabit ports active between switches. The links must have the same speed, duplex setting, and VLAN configuration.

28. Further Study Links STUDY RESOUCES
g-101-Understanding-Spanning-Tree.htm
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