Advanced Switching Concepts.ppt 354x6z

CCNA Guide to Cisco Networking Fundamentals

Chapter 13 Advanced Switching Concepts

Objectives • Explain how the Spanning Tree Protocol works and describe its benefits • Describe the benefits of virtual LANs • Configure a VLAN • Understand the Purpose of the VLAN trunking protocol (VTP) • Configure VTP

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Spanning Tree Protocol • Physical path loops – A physical connection created when network devices are connected to one another by two or more physical media links – Help improve a network’s fault tolerance

• Drawback – Can result in endless packet looping

• Spanning Tree Protocol (SP) – A layer 2 link management protocol designed to prevent looping on bridges and switches – The specification for STP is IEEE 802.1d CCNA Guide to Cisco Networking Fundamentals

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Spanning Tree Protocol (continued)

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Spanning Tree Protocol (continued) • STP uses the Spanning Tree Algorithm (STA) – To interrupt the logical loop created by a physical loop in a bridged/switched environment – STP does this by ensuring that certain ports on some of the bridges and switches do not forward frames

• Building a logical path – Switches and bridges on a network use an election process to configure a single logical path – First, a root bridge (root device) is selected – Then, the other switches and bridges configure their ports, using the root bridge as a point of reference CCNA Guide to Cisco Networking Fundamentals

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Spanning Tree Protocol (continued) • Bridges use STP to transfer the information about each bridge’s MAC address and priority number • Bridge protocol data units (BPDU) or configuration bridge protocol data units (CBPDU) – The messages the devices send to one another

• Each bridge or switch determines which of its own ports offers the best path to the root bridge • Root ports – The BPDU messages are sent between the root bridge and the best ports on the other devices CCNA Guide to Cisco Networking Fundamentals

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Spanning Tree Protocol (continued) • If BPDUs are not received for a certain period of time – The non-root-bridge devices will assume that the root bridge has failed, and a new root bridge will be elected

• Once the root bridge is determined and the switches and bridges have calculated their paths to the root bridge – The logical loop is removed by one of the switches or bridges

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Spanning Tree Protocol (continued) • Port states – STP will cause the ports on a switch or bridge to settle into a stable state

• Stable states – The normal operating states of ports when the root bridge is available and all paths are functioning as expected

• Transitory states – Prevent logical loops during a period of transition from one root bridge to another CCNA Guide to Cisco Networking Fundamentals

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Spanning Tree Protocol (continued) • The stable states are as follows: – Blocking – Forwarding – Disabled

• The transitory states are as follows: – Listening – Learning

• STP devices use the transitory states on ports while a new root bridge is being elected CCNA Guide to Cisco Networking Fundamentals

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Spanning Tree Protocol (continued) • Ports on STP-enabled devices move through the different states as indicated in the following list: – – – – –

From bridge/switch bootup to blocking From blocking to listening (or to disabled) From listening to learning (or to disabled) From learning to forwarding (or to disabled) From forwarding to disabled

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Spanning Tree Protocol (continued) • Topology changes – When the topology is changed, STP-enabled devices react automatically – If a device in an STP-enabled network stops receiving CBPDUs, then that device will claim to be the root bridge • Will begin sending CBPDUs describing itself as such

• Per-VLAN STP (PVSTP) – Operates on VLANs and treats all VLANs connected as separate physical networks CCNA Guide to Cisco Networking Fundamentals

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Spanning Tree Protocol (continued) • Spanning Tree PortFast – Allows you to configure a switch to by some of the latency (delay) • Associated with the switch ports transitioning through all of the STP transitory states before they reach the forwarding state

• Configuring STP – See Table 13-1

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Spanning Tree Protocol (continued)

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Spanning Tree Protocol (continued) • Rapid STP (RSTP) 802.1w – Takes the basis of 802.1d (STP) and incorporates some additional features (such as portfast) that overcome some of the flaws of STP

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Virtual LANs • Virtual LAN (VLAN) – A grouping of network devices that is not restricted to a physical segment or switch – Can be configured on most switches to restructure broadcast domains

• Broadcast domain – Group of network devices that will receive LAN broadcast traffic from each other

• Management VLAN (also known as the default VLAN) – By default, every port on a switch is in VLAN 1 CCNA Guide to Cisco Networking Fundamentals

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Virtual LANs (continued) • You can create multiple VLANs on a single switch – Or even create one VLAN across multiple switches

• A VLAN is a layer 2 implementation, and does not affect layer 3 logical addressing

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Virtual LANs (continued)

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Virtual LANs (continued)

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Benefits of VLANs • Benefits: – – – –

Ease of adding and moving stations on the LAN Ease of reconfiguring the LAN Better traffic control Increased security

• VLANs help to reduce the cost of moving employees from one location to another – Many changes can be made at the switch – Physical moves do not necessitate the changing of IP addresses and subnets CCNA Guide to Cisco Networking Fundamentals

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Benefits of VLANs (continued) • Because the can set the size of the broadcast domain – The VLAN gives the added control over network traffic

• Dividing the broadcast domains into logical groups increases security – Requires a hacker to perform the difficult feat of tapping a network port and then figuring out the configuration of the LAN

• VLANs can be configured by network s to allow hip only for certain devices CCNA Guide to Cisco Networking Fundamentals

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Dynamic vs. Static VLANs • Static VLANs – Configured port-by-port, with each port being associated with a particular VLAN – The network manually types in the mapping for each port and VLAN

• Dynamic VLAN – Ports can automatically determine their VLAN configuration – Uses a software database of MAC address-to-VLAN mappings that is created manually CCNA Guide to Cisco Networking Fundamentals

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Dynamic vs. Static VLANs (continued) • Dynamic VLAN could prove to be more timeconsuming than the static VLAN • Dynamic VLAN allows the network istration team to keep the entire istrative database in one location • On a dynamic VLAN, moving a cable from one switch port to another is not a problem – Because the VLAN will automatically reconfigure its ports on the basis of the attached workstation’s MAC address CCNA Guide to Cisco Networking Fundamentals

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VLAN Standardization • Before VLAN was an IEEE standard – Early implementations depended on the switch vendor and on a method known as frame filtering

• Frame filtering – Complex process that involved one table for each VLAN – Had a master table that was shared by all VLANs

• The IEEE 802.1q specification that defines VLANs recommends frame tagging – Also known as frame identification CCNA Guide to Cisco Networking Fundamentals

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VLAN Standardization (continued) • Frame tagging – Involves adding a four-byte field to the actual Ethernet frame to identify the VLAN and other pertinent information – Makes it easier and more efficient to ship VLAN frames across network backbones • Switches on the other side of the backbone can simply read the frame instead of being required to refer back to a framefiltering table

• The two most common types of frame tagging (encapsulation) are 802.1q and Inter-Switch Link (ISL) protocol CCNA Guide to Cisco Networking Fundamentals

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Creating VLANs • You can create VLANs by entering the (configvlan)# mode and using the VLAN command – Or you can enter the VLAN database and use the VLAN configuration mode

• To use the config-vlan mode, you type the following: – Rm410HL(config)#VLAN 2 – Rm410HL(config-vlan)name production

• To use the VLAN configuration mode, you start by entering the VLAN database

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Creating VLANs (continued) • The next step is to assign switch ports to the new VLANs – Ports can be assigned as static or dynamic

• To remove a VLAN, use the no parameter: – Rm410HL(config)#no vlan 2

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Link Types and Configuration • Two types of links are on Cisco switches: trunk links and access links • Trunk links – Switch-to- switch or switch-to-router links that can carry traffic from multiple VLANs

• Access links – Links to non-VLAN-aware devices such as hubs and individual workstations

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Link Types and Configuration (continued) • You choose from five different states for a trunk link: – – – – –

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• To configure a trunk link on a Catalyst 2950, you must be in the appropriate interface configuration mode CCNA Guide to Cisco Networking Fundamentals

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Link Types and Configuration (continued) • Switch interface descriptions – You can configure a name for each port on a switch – This is useful when you begin to define roles for a switch port on a more global basis

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VLAN Trunking Protocol • VLAN trunking protocol (VTP) – Created by Cisco to manage all of the configured VLANs that traverse trunks between switches – A layer 2 messaging protocol that manages all the changes to the VLANs across networks

• VTP domains – VTP devices are organized into domains – Each switch can only be in one VTP domain at a time • All devices that need to share information must be in the same VTP domain CCNA Guide to Cisco Networking Fundamentals

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VLAN Trunking Protocol (continued) • VTP device modes – Server • Device can add, rename, and delete VLANs and propagate those changes to the rest of the VTP devices

– Client • Device is not allowed to make changes to the VLAN structure, but it can receive, interpret, and propagate changes made by a server

– Transparent • A device is not participating in VTP communications, other than to forward that information through its configured trunk links CCNA Guide to Cisco Networking Fundamentals

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VLAN Trunking Protocol (continued) • VTP pruning option – Reduces the number of VTP updates that traverse a link – Off by default on all switches

• If you turn VTP pruning on – VTP message broadcasts are only sent through trunk links that must have the information

• VLAN 1 is not eligible to be pruned because it is an istrative (and default) VLAN

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Nonswitching Hubs and VLANs • Important considerations: – If you insert a hub into a port on the switch and then connect several devices to the hub, all the systems attached to that hub will be in the same VLAN – If you must move a single workstation that is attached to a hub with several workstations, you will have to physically attach the device to another hub or switch port to change its VLAN assignment – The more hosts that are attached to individual switch ports, the greater the microsegmentation and flexibility the VLAN can offer CCNA Guide to Cisco Networking Fundamentals

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Routers and VLANs • Routers can be used with VLANs to increase security – Must be used to manage traffic between different VLANs

• Routers can implement access lists – Which increase inter-VLAN security

• A router allows restrictions to be placed on station addresses, application types, and protocol types

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Routers and VLANs (continued) • Router can either be an onboard Route Switch Module (RSM) or an external router • The router will accept the frame tagged by the sending VLAN and determine the best path to the destination address – The router will then switch the packet to the appropriate interface and forward it to the destination address

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Routers and VLANs (continued) • Router-on-a-stick – If a single link is used to connect an external router with the switch containing multiple VLANs • Trunking is required for inter-VLAN routing

• Trunking is the process of using either ISL or 802.1q to allow multiple VLAN traffic on the same link – For instance, an ISL trunk link would encapsulate each packet with the associated VLAN information and allow the router to route the packet accordingly

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Summary • The Spanning Tree Protocol (STP) allows s to create physical loops between bridges and switches – Without creating logical loops that would pose a problem for packet delivery

• The Rapid Spanning Tree Protocol (RSTP) has enhanced STP to reduce the latency associated with convergence • Implementing VLANs via switches provides another way to increase the performance, flexibility, and security of a network CCNA Guide to Cisco Networking Fundamentals

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Summary (continued) • VLANs are separate broadcast domains that are not limited by physical configurations • Performance benefits associated with VLANs are derived from limiting the amount of broadcast traffic that would naturally through a switch without filtration • Because traffic on a VLAN broadcast can be limited to a specific group of computers, security is also enhanced by making it more difficult for eavesdropping systems to learn the configuration of a network CCNA Guide to Cisco Networking Fundamentals

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Summary (continued) • VLAN information is communicated to switches using the VLAN trunking protocol (VTP)

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