Bridging and Switching Fundamentals

7/27/2019 Bridging and Switching Fundamentals

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Cisco CCNP SWITCH TrainingInstructor: Joe Rinehart, CCIE #14256

Bridging and

SwitchingFundamentals

Cisco CCNP SWITCH Training

Bridging and Switching Fundamentals

In This Lesson:

Bridging Theory

Hubs, Bridges and Switches

Cisco Switch Specifics

Contrasting Layer 3 Switching and Routing

Configuring Bridging on Routers



Bridging Theory

1. Development of Local Area Networks

2. Operation of LAN Bridges

3. Types of Bridging

4. Bridging Functions on Cisco Routers





Bridging Theory

Development of Local Area Networks

• Local Area Networks Emerged in 1970’s

–Early versions used heavy cabling

–Ethernet, ARCNet and Token Ringwere early technologies

• Information Sharing was One Goal

–Printer sharing

–File exchange

– Interaction with servers

• E-Mail

• Internet

• Applications



Bridging Theory

Development of Local Area Networks

• Hubs and Repeaters Increased Access

–Enabled more users on the network

–Created more collisions and trafficissues

–Degradation of network bandwidth

–Performance issues rose sharply

–No ability to enforce any type of traffic control

• Bridges and Later Switches Addressed

Traffic Control and LAN PerformanceIssues



Bridging Theory

Operation of LAN Bridges

• Bridges Segment Networks at Layer 2

–Two port devices that createdseparate collision domains (see left)

–Operates at Layer 2

–Builds a table to track MAC addressesand the port it came in from

• Takes one of three actions on frames:

–Flood: For unknown unicasts and

broadcasts, send out all ports butsource port

–Forward: Transmit out other port(s)

–Filter: Drop the frame





Bridging Theory

Types of Bridging

• Older Bridging Methods

–Source Route Bridging

–Translational Bridging

–Data Link Switching

• Transparent Bridging is Most Common

–Devices have no awareness of thebridge device

–Requires loop avoidance mechanisms(such as Spanning Tree, consideredlater)

–Forms the basic logic of Ciscoswitching devices



Bridging Theory

Bridging Functions on Cisco Routers

• Transparent Bridging

–Functions the same way as switches

–Bridges traffic between interfaces

–Taxes the CPU and router resources

• Concurrent Routing and Bridging (CRB)

–Permits the device to route and bridgethe same protocol (e.g., IP)

–Keeps both separate

• Integrated Routing and Bridging

–Creation of a special bridginginterface

–Can route and bridge at same time



Bridging Theory

Bridging Functions on Cisco Routers

• Reasons to Bridge Traffic

–Transport of non-routable traffic(NETBIOS, for example)

–Wireless traffic

• Configuration Process

–Creation of bridge using bridge <#><protocol> command

–Configuration of the bridging interface

using the interface BVI <#>command

–Placing interfaces in the bridge withthe bridge-group <#> command






1. Layer 1 Network Extension: Hubs

2. Layer 2 Network Extension: Bridges

3. Layer 2 Network Segmentation: Switches




Layer 1 Network Extension: Hubs

• Characteristics of Hubs

–Functions at Layer 1

–Essentially a multiport repeater

– Increases the collision domain

–Half-Duplex by nature

• Drawback to Hubs

–Generally obsolete in most networks

– All bandwidth is shared amongconnected devices

– Increases the amount of collisionsand degrades performance with eachstation added




Layer 2 Network Extension: Bridges

• Characteristics of Bridges

–Functions at Layer 2

– Increases the broadcast domain

–Reduces the collision domain

–Half-Duplex by nature

–Filters traffic by Layer 2 address

• Drawback to Bridges

–Generally obsolete in most networks

– Increases the amount of broadcasts

–Full duplex operation impossible

–Limited to two ports






Layer 2 Network Segmentation:Switches

• Characteristics of Switches

–Functions at Layer 2 or 3

– Increases the broadcast domain

–Reduces the collision domain

–Full-Duplex Capable

–Filters traffic by Layer 2 address

• Drawback to Switches

–Simple ones have no managementcapabilities

–Layer 2 switches require routers forLayer 3 functions




1. LAN Switching Methods

2. Duplex Settings/Types

3. Cisco Switch OS Types

4. Application Specific Integrated Circuit(s)




LAN Switching Methods

• Store and Forward

–Original switching method

–Copies the entire frame beforetransmitting

–Most error-free method

–Originally superseded by others

• Cut-Through

–Copies first 6 bytes (e.g., destination

address) before transmitting

– Very low latency

–Collisions and other errors may goundetected






LAN Switching Methods

• Fragment-Free

–Copies and examines first 64 bytes of frames

–Most errors and collisions will bedetected in the first 64 bytes of an

Ethernet frame

–Low latency with lower error rates

• Methods in Use Today

–Cut-Through and Fragment-Freebecame widely used in early switches

–Faster circuitry lessened latency

–Shorter methods still used today




Duplex Settings/Types

• Simplex

–Data is sent in one direction only

–Not a typical function in mostnetworks today

–Similar to broadcast media (Radio/TV)

• Half-Duplex

–Data is sent in both directions butonly one direction at a time

–Common in hub based networks

–Default with older 10 Mbps Ethernet –Collisions still possible

–Still occasionally encountered today




Duplex Settings/Types

• Full-Duplex

–Data is sent in both directionssimultaneously

– Increases bandwidth and throughput

–Similar to broadcast media (Radio/TV)

• Cisco Router/Switch Duplex Defaults

–10 Mbps Ethernet: Half-Duplex

–10/100 Mbps Ethernet: Full-Duplex

–10/100/1000 Mbps Ethernet: Full-Duplex

–10 Gbps Ethernet: Full-Duplex






Cisco Catalyst Switch OS Types

• CatOS (Catalyst Operating System)

–Originally developed by CrescendoCommunications before acquisition byCisco

–Used on chassis based switches

• 4000/4500 series

• 5000/5500 series (now EOL)

• 6000/6500 series (now EOL)

• Native IOS

–Switch-based version of IOS

–Default

• Hybrid (CatOS and IOS together)

www.cisco.com




Application Specific IntegratedCircuit(s)

• Hardware-Based Forwarding

–Forwards traffic based on L2 o r L3

–Critical component of Catalystswitches

–Performs switching in hardware ratherthan software

– Vastly increases processing speed(termed “wire rate” speed)

–

Port-based ASIC –More dynamics of the architecture

discussed later

www.cisco.com



Contrasting Layer 3 Switching and Routing1. Basic Differences Between Routers and Switches

2. Router Traffic Flow

3. Layer 3 Switch Traffic Flow

http://www.cisco.com/









Basic Differences Between Routersand Switches

• Forwarding Architecture

–Routers perform packet switching androuting decisions in software (involvesCPU)

–Switches perform packet switching inhardware using ASICs

• Management

–Both router and switches haveconsole ports for out-of-band access

–Only routers have AUX port

–Both have similar CLI functions

www.cisco.com




Basic Differences Between Routersand Switches

• Interfaces

–Most switches only have Ethernet

ports (10/100/1000/10 Gbps)

–Routers support many interfaces

• LAN (Ethernet)

• Serial

• BVI

• Tunnel

• Asynchronous• 802.11 Wireless

• Others

www.cisco.com




Basic Differences Between Routers

and Switches• Capabilities

–Routers and Layer 3 switches support

IP routing, multicast, access-lists, etc.

–Routers support Network AddressTranslation, switches do not

–Routers require special configurationfor VLAN support, switches do not

–Routers support telephonytechnologies natively, most switchesdo not

–Routers have firewall capabilities mostswitches so not

www.cisco.com












Router Traffic Flow

• Packet Processing Steps (see left)

–Layer 2 (Ethernet) performs FCScheck and frame validation (FA0/1)

–Layer 3 packet check performed

–Route lookup and forwarding decision

made

–Layer 2 frame is rewritten with thesource MAC of the outgoing interface(FA0/1) and destination MAC of thenext-hop

–Frame is forwarded out destinationinterface (FA0/2)

Richard Froom,Implement ing Cisco IP Swi tched Networks , Cisco Press, 2010




Layer 3 Switch Traffic Flow

• Packet Processing Steps (see left)

–Layer 2 (Ethernet) performs FCScheck and frame validation (FA0/0)

–Layer 2 header is stripped off

–Layer 3 packet check performed

–Route lookup and forwarding decisionmade

–New Layer 2 frame created with next-hop MAC address as destination

–Frame is forwarded out destinationinterface (FA0/1)

AlexZinn,Cisco IP Rout ing , Cisco Press, 2001




1. Bridging Configuration Elements

2. Bridging Commands

3. Verifying Bridging






Bridging Configuration Elements

• Bridge/Bridge-Group

–Created with the bridge <bridge#>protocol<protocol> command

–Number is locally significant to therouter

–Multiple bridges can be created

–Spanning tree protocol typessupported:

• IEEE

• DEC

• VLAN-Bridge




Bridging Configuration Elements

• Interfaces

– Added individually with the bridge-group <bridge#> command in

interface configuration mode

–Number must match the previouslydefined bridging group

–Bridged Virtual Interface optional(must match bridge number)

• Enabling Integrated Routing and Bridging

–

Not enabled by default –Feature enacted using the bridge irb

command in global configurationmode




Bridging Commands

• Configuring Integrated Routing andBridging

–Enter bridge irb command in global

configuration mode on R1-1, R1-2 andR3-1

• Creation of Bridge-Group 1

–Enter bridge 1 protocol ieeecommand in global configuration

mode on R1-1, R1-2 and R3-1

• Place Loopback 0 and Fast Ethernet 0/0interfaces in the bridge group

–Enter bridge-group 1 on R1-1, R1-2and R3-1 interfaces






Verifying Bridging

• Verifying Bridging Operation

–Execute show bridge [bridge#][verbose] to confirm operationalstatus of bridge-group

–Execute show spanning-tree [bridge]

to confirm spanning tree configuration(automatically enacted for bridgegroups)

–Perform ping/extended ping testsusing Loopback interfaces (successfulping verifies correct bridge group

configuration and operation)



Key Terms You Should Know

Bridging — Layer 2 forwarding process which floods, forwards,or filters traffic depending on destination MAC addresses

IRB — Integrated Routing and Bridging, Cisco router-basedfeature which allows the device to both route and bridge the

same protocol(s)

ASIC — Application Specific Integrated Circuit, hardware-basedcircuitry used for various Cisco switch-based functions at Layer2

Half-Duplex — Refers to the ability to send network traffic inboth directions (e.g., sending/receiving) but only one at a time

Full-Duplex — Refers to the ability to send network traffic in

both directions (e.g., sending/receiving) at the same time

CatOS — Catalyst Operating System, an older Cisco switchoperating system, now obsolete



What We Covered

Bridging Theory





Bridging and Switching Fundamentals

Documents

Transcript of Bridging and Switching Fundamentals