CIT 384: Network AdministrationSlide #1 CIT 384: Network Administration Switches

CIT 384: Network AdministrationSlide #2 Topics 1.TCP/IP Architecture 2.OSI Reference Model 3.Cisco certification overview

CIT 384: Network AdministrationSlide #3 Switching at Data Link Layer Forwards Ethernet frames between two devices on same LAN. Logical link control –Flow control –Error correction Media access control –Who can transmit when. –Breaks data into frames. Application Presentation Session Transport Network Data Link Physical

CIT 384: Network AdministrationSlide #4 Hubs Advantages over 10BASE2 bus –Problem on 1 cable didn’t impact entire network. –Easier to run cables for star topology. Disadvantages of hubs –Collisions –Shared bandwidth, only one device can send at a time. –Broadcasts seen by all hosts.

CIT 384: Network AdministrationSlide #5 Bridges A bridge segments a network into two parts. –Each part is a collision domain. –Frames in domain A can collide with each other. –But they cannot collide with frames in domain B. Bridges buffer packets. –If domain A is busy, then frame is buffered until the segment is no longer busy.

CIT 384: Network AdministrationSlide #6 Bridges Bridges reduce collisions + add bandwidth.

CIT 384: Network AdministrationSlide #7 Switches A switch works like a collection of bridges. –Each port is its own collision domain. –If only one device connected to a port, the switch can communicate at full duplex.

CIT 384: Network AdministrationSlide #8 Ethernet Address Types Unicast addresses represent a single device. Multicast addresses represent a subset of devices on the LAN. They begin with E The broadcast address represents all devices on the LAN. It is FFFF.FFFF.FFFF

CIT 384: Network AdministrationSlide #9 Switch Functions 1.Decide whether to forward a frame or not, based on its destination MAC address. 2.Learn MAC addresses by examining source MAC addresses received. 3.Create a layer 2 loop-free environment using Spanning Tree Protocol (STP.)

CIT 384: Network AdministrationSlide #10 Forwarding Frames 1.Switch receives frame on a port. 2.Extracts destination MAC address from Ethernet header. 3.Looks up destination MAC address in internal address table. 4.Forwards frame to port specified in table unless that port is the same port on which the frame was received. 5.If no entry exists in table for MAC address, forward the frame out all interfaces except the port it originated from.

CIT 384: Network AdministrationSlide #11

CIT 384: Network AdministrationSlide #12 Learning MAC Addresses 1.Switch receives frame on a post. 2.Retrieves source MAC address from Ethernet header of frame. 3.Searches address table for MAC address. 4.If MAC address not found, add the (MAC address, port) pair to the table.

CIT 384: Network AdministrationSlide #13 MAC Address Table Switches have a finite amount of memory. –Can only store a fixed # of addresses. Maintain an inactivity timer for each address. –Timer reset to 0 each time address is seen. –If switch runs out of space, oldest entries are removed from table.

CIT 384: Network AdministrationSlide #14 Loops Bob is off, so no switch has his address. Therefore switches flood frames to Bob. Switches receive flood from other switches, which they flood again, looping indefinitely.

CIT 384: Network AdministrationSlide #15 Avoiding Loops Don’t have physically redundant switches. –Redundancy is needed for reliability. –It’s easy for someone to add a switch and create a loop in a complex campus network. Create a logical network without loops: STP. –Dynamically disable switch ports that could allow loops. –Re-enable disabled ports when a link fails so that network retains benefit of redundancy.

CIT 384: Network AdministrationSlide #16 Collision Domains A collision domain is the set of devices whose frames can collide with each other. Bridges, switches, and routers separate the network into collision domains.

CIT 384: Network AdministrationSlide #17 Collision Domains All devices share the available bandwidth. Bandwidth may be inefficiently used due to effects of collision, especially under high use.

CIT 384: Network AdministrationSlide #18 Broadcast Domains A broadcast domain is the set of devices for which, when one device sends a broadcast, all devices receive the broadcast. Routers separate the network into broadcast domains.

CIT 384: Network AdministrationSlide #19 Broadcast Domains Bandwidth is not shared. Some bandwidth and processing may be wasted by broadcasts in large domains. A LAN consists of all devices in the same broadcast domain.

CIT 384: Network AdministrationSlide #20 Segmenting Device Features FeatureHubSwitchRouter Greater cabling distancesYes Multiple collision domainsNoYes Increases bandwidthNoYes Multiple broadcast domainsNo Yes

CIT 384: Network AdministrationSlide #21 Virtual LANs (VLANs) Without VLANs, switches consider all devices on same broadcast domain (LAN.) With VLANs  Switch can support multiple broadcast domains.  Assign ports to specific VLANs.

CIT 384: Network AdministrationSlide #22 VLAN Purposes Create more flexible network designs, without having more switches. Segment devices into smaller broadcast domains to increase performance. Reduce STP workload by limiting VLAN to a single access switch. To enforce security by aggregating sensitive hsots on specific VLANs. To separate VOIP traffic from PC traffic.

CIT 384: Network AdministrationSlide #23 Switch Design Hierarchy Three layers –Access –Distribution –Core Differences –Whether switch connects to end-user devices. –Whether switch should forward frames between other switches by connecting to multiple different switches.

CIT 384: Network AdministrationSlide #24 Switch Layers Access switches –Connect directly to end- user devices. –Send traffic to connected end-user devices. –Send other traffic to distribution layer. Models –Catalyst 3750 –Catalyst 3560 –Catalyst 2960 Catalyst 3750 switches

CIT 384: Network AdministrationSlide #25 Distribution Switches Provide path through which access switches can forward traffic to each other. Models –Catalyst 6500 –Catalyst 4500

CIT 384: Network AdministrationSlide #26 Core Switches Aggregate distribution switches. Not needed on smaller networks. Models –Catalyst 6500 –Nexus 7000

CIT 384: Network AdministrationSlide #27

CIT 384: Network AdministrationSlide #28 Catalyst 2960 Ethernet ports – TT-L: 24 10/ /100/1000 ports –Series ranges from 8+1 to 48 gigabit ports. Operating System: Cisco IOS Other features –Some models support Power over Ethernet –QoS support for IP phones –Security features (MAC binding, NAC)

CIT 384: Network AdministrationSlide #29 Catalyst 2960 LEDs #NameDescription 1SYSTgreen=up; amber=POST failed; off=powered off 2RPSStatus of redundant power supply 3STATIf on, each port: on=up, no traffic, flash green=up, traffic, flashing amber=port is disabled 4DUPLXIf on, each port: on is full duplex, off is half duplex 5SPEEDIf on, each port: off=10, solid=100, flashing=1000 7PortIndividual port LED; see above for meanings

CIT 384: Network AdministrationSlide #30 Accessing the IOS CLI

CIT 384: Network AdministrationSlide #31 CLI Access Methods Console  9600 bps 8N1 serial connection  Available before switch has been configured.  Available during problems: down network, OS.  Only one connection at a time. ssh and telnet  Switch must be configured with an IP address.  Provides remote access from anywhere on net.  Up to 16 simultaneous connections.  All data (including passwords) revealed by telnet, so ssh is preferred.

CIT 384: Network AdministrationSlide #32 CLI configuration Access TypeConfiguration Consoleline console 0 login password spam telnetline vty 0 15 login password eggs

CIT 384: Network AdministrationSlide #33 User and Enable Mode User Exec mode can read most data. Enable mode is needed to reconfigure switch.

CIT 384: Network AdministrationSlide #34 Cisco IOS Internetwork Operating System –Multitasking, no memory protection –CLI copied by many network vendors. IOS is available with different feature sets: –IP data –Voice + data –Security + VPN Older switches run CatOS

CIT 384: Network AdministrationSlide #35 CLI Help Features What you TypeHelp provided ?Help for all commands in this mode. helpMessage describing how to get help. command ?Help describing all of the first options for command. command parm?Help describing all of the first options for command that begin with parm. command parm Command completion. command parm1 ?Help describing all of the second options for command where parm1 is the first parameter.

CIT 384: Network AdministrationSlide #36 CLI Editing KeystrokeEffect up arrowCommand history (backward) down arrowCommand history (forward) left arrowMove backward one character in current command line. right arrowMove forward one character in current command line. backspaceMove backward and delete one character. ctrl-aMove cursor to first character of command line. ctrl-eMost cursor to end of the command line. ctrl-rRedisplays command line with all characters. Useful when console messages clutter the screen. ctrl-dDeletes a single character esc-bMove cursor backward one word. esc-fMove cursor forward one word.

CIT 384: Network AdministrationSlide #37 Configuration Mode Commands in Configuration Mode update the active configuration file.

CIT 384: Network AdministrationSlide #38 Configuration Submodes PromptMode NameCommand to reach host(config)#Globalconfigure terminal host(config-line)#Lineline console 0 line vty 0 15 host(config-if)#Interfaceinterface type # host(config-router)#Routerrouter ospf router igrp

CIT 384: Network AdministrationSlide #39 Example CLI Session Switch> enable Switch# configure terminal Switch(config)# enable secret letmein Switch(config)# interface FastEthernet 0/1 Switch(config-if)# speed 100 Switch(config-if)# ip address Switch(config-if)# no shutdown Switch(config-if)# exit Switch(config)# line console 0 Switch(config-line)# password spam Switch(config-line)# exit Switch(config)# copy running-config startup-config Switch(config)# disable Switch>

CIT 384: Network AdministrationSlide #40 Switch Memory Types RAM: Working storage, includes the active configuration file. ROM: Stores boot program that finds Cisco IOS image and loads into RAM. Flash: Stores IOS image and other files. NVRAM: Stores startup configuration file that is used when switch is booted.

CIT 384: Network AdministrationSlide #41 Switch Configurations Configurations Running: currently used config in RAM. Startup: will be used at next reboot. Viewing show running-config show startup-config Saving running-config (replaces old startup) copy running-config startup-config

CIT 384: Network AdministrationSlide #42 References 1.James Boney, Cisco IOS in a Nutshell, 2 nd edition, O’Reilly, Cisco, Catalyst 2960 series switches, Cisco, Cisco Connection Documentation, Cisco, Internetworking Basics, m 5.Wendell Odom, CCNA Official Exam Certification Library, 3 rd edition, Cisco Press, Priscilla Oppenheimer and Joseph Bardwell, Troubleshooting Campus Networks, Addison-Wesley, W. Richard Stevens, TCP/IP Illustrated, Addison-Wesley, 1994.