CCENT Section 2 – Flashcards

Local-area networks (LAN) are high-speed, low-error data networks that cover a small geographic area. LANs are usually located in a building or campus and do not cover a large distance. They are relatively inexpensive to develop and maintain. LANs connect computers, printers, and other devices in a single building or a limited area.

LAN standards define the physical media and connectors used to connect to the media at the physical layer and the way devices communicate at the data link layer. LAN standards encompass Layers 1 and 2 of the OSI model. An example of a LAN standard is Ethernet, which is also known as 802.3.

Typical components found in LANs are Computers: PCs, servers, tablets Interconnections: NICs, media Network devices: Switches, routers, access points Protocols: Ethernet, IP, ARP, DHCP

Bus. Ethernet uses a logical bus topology and either a physical bus or star topology.

Two types of Layer 1 network devices are as follows: Image Repeaters: Regenerate and retime network signals, allowing the signal to travel a longer distance on a network media. Image Hubs: Known as a multiple-port repeaters, hubs also regenerate and retime network signals. The main difference between a hub and a repeater is the number of ports a hub has. A repeater typically has two ports, whereas a hub has from 4 to 48 ports. NOTE:In Ethernet networks, both hubs and repeaters share the LAN bandwidth. All devices compete to use network bandwidth, and only one device can access the network at a time. For example, if you have ten devices connected to a 100-Mbps hub, all ten devices share the 100 Mbps of bandwidth.

Bridges and switches are network devices that operate at the data link layer. Both devices make decisions about what traffic to forward, flood, or drop (filter) by MAC addresses, and logical network addresses are not used at this layer. Data link layer devices assume a flat address space. Typically, a bridge is designed to create two or more LAN segments and is software implemented. A switch is a hardware version of a bridge, has many more ports than a bridge, and is designed to replace a hub while providing the filtering benefits of a bridge.

A LAN segment is a network connection made by a single unbroken network cable. Segments are limited by physical distance because, after a certain distance, the data transmission becomes degraded because of line noise and the reduction of signal strength.

To extend a LAN segment, you can use the following devices: Hubs Repeaters Bridges Switches

Collisions occur on a shared LAN segment when two devices try to communicate at the same time. In a shared Ethernet segment, only one device can transmit on the cable at a time. When two devices try to transmit at the same time, a collision occurs. When a collision occurs, a jam signal is sent from a workstation. A collision affects all the machines on the segment, not just the two that collided; when the jam signal is on the wire, no workstations can transmit data. The more collisions that occur in a network, the slower it will be, because the devices must resend the packets that collided.

A collision domain is set of LAN interfaces whose frames could collide with each other. For example, all devices connected to a hub are in the same collision domain.

Hubs and repeaters operate at the physical layer of the OSI model; segmenting a network with these devices appears as an extension to the physical cable. Hubs and repeaters are transparent to devices; they are unintelligent devices. All devices that connect to a hub/repeater share the same bandwidth. Hubs/repeaters create a single broadcast and collision domain.

Switches operate at Layer 2 of the OSI model and filter and forward by MAC address. Each port on a switch provides fully dedicated bandwidth and creates a single collision domain. Because switches operate at Layer 2 of the OSI model, they cannot filter broadcasts, and they create a single broadcast domain.

Switches, bridges, and routers are used to break up collision domains. They create more collision domains and result in fewer network collisions. Each port on a bridge, switch, and router creates one collision domain. For example, if you have a switch with 24 ports, you have 24 separate collision domains.

You will have one collision domain. A hub only extends the Ethernet segment, and all devices share the same segment bandwidth. As a result, a hub does not create more collision domains.

You will have 24 collision domains and one broadcast domain. Switches operate at Layer 2 of the OSI model, and they divide the network into different segments, thus creating more collision domains. Each port on a switch creates one collision domain. Also, because a switch operates at Layer 2 of the OSI model, it cannot filter broadcasts. As such, a switched network will have one broadcast domain.

A broadcast domain defines a group of devices that receive each other's broadcast messages. As with collisions, the more broadcasts that occur on the network, the slower the network will be. This is because every device that receives a broadcast must process it to see whether the broadcast is intended for that device. Note: Although too many broadcasts can slow your network, they are used by many protocols for communications. To avoid excessive broadcasts, segment your network with routers or Layer 3 switches.

Six collision domains and six broadcast domains will be created. Each interface on a router creates a collision domain and a broadcast domain.

Broadcast storms occur when many broadcasts are sent simultaneously across all network segments. They are usually caused by Layer 2 loops because of spanning tree misconfigurations, a bad network interface card (NIC), a faulty network device, or a virus.

The three primary functions that Layer 2 switches provide are as follows: MAC address learning Frame forwarding/filtering Loop avoidance with the Spanning Tree Protocol

Switches are Layer 2 devices and make forwarding decisions based on Layer 2 information. Hubs operate on Layer 1. Switches make forwarding decisions based on Layer 2 information by learning MAC addresses on incoming frames and storing these frames in a MAC address table.

Microsegmentation is a network design (functionality) where each workstation or device on a network gets its own dedicated segment (collision domain) to the switch. Each network device gets the full bandwidth of the segment and does not have to contend or share the segment with other devices. Microsegmentation reduces collisions because each segment is its own collision domain.

A switch considers each LAN port to be an individual segment. The advantages offered by LAN segmentation using LAN switches are as follows: Collision-free domains from one larger collision domain Efficient use of bandwidth with full duplex Low latency and high frame-forwarding rates at each interface port

The three frame operating modes to handle frame switching are as follows: Store-and-forward Cut-through Fragment-free

In the store-and-forward switching method, the switch's incoming interface receives the entire frame before it forwards it. The switch compares the last field in the datagram, the cyclic redundancy check (CRC), against its own frame check sequence (FCS) calculations to make sure that the frame is free from physical and data-link errors. If the switch observes any errors in the FCS calculations, the frame is dropped. If the frame is a runt (less than 64 bytes, including the CRC) or a giant (more than 1518 bytes, including the CRC), the switch discards it. Because the switch stores the frame before forwarding it, latency is introduced in the switch. Latency through the switch varies with the size of the frame.

In cut-through switching mode, the switch only checks the frame's destination address and immediately begins forwarding the frame out the appropriate port. Because the switch checks the destination address in only the header and not the entire frame, the switch forwards a frame that has a bad CRC calculation.

Also known as modified cut-through, fragment-free switching checks the first 64 bytes of the frame before forwarding the frame. If the frame is less than 64 bytes, the switch discards the frame. Ethernet specifications state that collisions should be detected during the first 64 bytes of the frame. By reading the first 64 bytes of the frame, the switch can filter most collisions, although late collisions are still possible.

Six ways to configure a Cisco device are as follows: Console connection Auxiliary connection (through a modem) Telnet connection HTTP/HTTPS connection Secure Shell (SSH) Connection Cisco Prime

You need an RJ-45-to-RJ-45 rollover cable. A rollover cable is a cable that has each pin wired to its opposite number at the other end.

The COM port configuration settings needed to connect to a Cisco device's console port are as follows: Speed: 9600 bits per second Data bits: 8 Parity: None Stop bit: 1 Flow control: None

The two Cisco IOS EXEC modes are User EXEC mode (user mode) Privileged EXEC mode (enable or privileged mode)

User EXEC mode allows a person to access only a limited number of basic monitoring commands. This mode is limited and is mostly used to view statistics. You cannot change a router's configuration in this mode. By default, the greater-than sign (>) indicates that you are in user mode. This is how the router prompt looks in user mode: RouterA> Note: You can change the default user-mode prompt and enable-mode prompt by using the prompt global mode command.

In privileged EXEC mode, you can view and change the configuration in a router; you have access to all the router's commands and the powerful debug commands. To enter privileged mode, enter the enable command while in user mode. By default, the pound symbol (#) indicates that you are in privileged mode. This mode is usually protected with a password. Here is an example of how to enter privileged mode. You also see the output of the prompt: Router> enable Password: Router#

You can return to user EXEC mode by using the disable IOS command. Here is an example of using the disable command: Router# disable Router>

Two types are word help and command syntax help. Word help uses a question mark (?) and identifies commands that start with a character or sequence of characters. For example, the following router output shows the use of word help for any IOS command that starts with the letters "cl": Router# cl? clear clock Command syntax help is when you use a question mark (?) after a command so that you can see how to complete the command. For example: Router# clock ? set Set the time and date

"% Ambiguous command" means that not enough characters were entered for the IOS to recognize the command.

You received the error because you did not enter all the values or keywords that IOS requires for this command. In this case, IOS does not know which show ip command you want to view.

You received the "% Invalid input detected at '^' marker" error because you entered the command incorrectly. For example, if you entered sjow ip instead of show ip, you would receive this error.

Global configuration commands are commands that affect the entire device. They can be executed only in global configuration mode.

To enter global configuration mode, you enter the configure terminal command from privileged EXEC mode, as follows: Router# configure terminal Enter configuration commands, one per line. End with CTRL-Z. Router(config)# Note Notice how the command prompt changes to (config)# in global configuration mode.

The enhanced editing commands are as follows: Move the cursor to the beginning of the line: Ctrl-A Move the cursor to the end of the line: Ctrl-E Move the cursor forward one word: Esc-F Move the cursor forward one character to the right: Ctrl-F Move the cursor back one character: Ctrl-B Delete all characters from the cursor back to the beginning of the command line: Ctrl-U

The show history command, by default, displays the last ten commands used. You can also use the up-arrow key (or press Ctrl-P) to display the very last command you entered and the down-arrow key (or press Ctrl-N) to display the previous commands you entered. As you use the up- or down-arrow keys, you are scrolling through the history buffer. The following is an example of the show history command: Router# show history en show running-config show history enable show version show clock show history Router#

To edit the number of command lines stored for the current session, use the terminal history [size number-of-lines] command in privileged EXEC mode. For example, the following changes the history size to 20 lines: Router# terminal history size 20 Note The maximum number of lines you can set for the current session is 256, but doing so wastes device memory.

When first powered up, an unconfigured switch enters the setup mode.

The names of the two configuration files are Running configuration: The current configuration of the device Startup configuration: The configuration file in NVRAM that is loaded when a Cisco device is powered up or rebooted

A switch enters setup mode if any of the following occur: The switch is a new switch, with no previous configuration. No configuration is stored in NVRAM. The setup command was issued from the privileged mode prompt.

RAM holds the router's routing table, packet buffers, and ARP cache. The running config is also stored in RAM. On most Cisco routers, the IOS is loaded into RAM as well.

On a Cisco device, ROM starts and maintains the router or switch.

Flash memory stores the Cisco IOS Software image and, if room exists, multiple configuration files or multiple IOS files for backup purposes. Flash memory is not erased when the router or switch is reloaded.

Nonvolatile random-access memory (NVRAM) holds the saved router or switch configuration. This configuration is maintained when the device is turned off or reloaded. NVRAM also stores boot system commands and the configuration register.

The show flash command displays the contents of flash memory. This includes the images stored in flash memory, the images' names, bytes used in flash memory, bytes available, and the total amount of flash memory on your router, as follows: cnat2-2901-1# show flash -#- --length-- -----date/time------ path 1 74856492 Apr 5 2012 18:43:10 +00:00 c2900 universalk9-mz.SPA.151-4.M3.bin 2 2903 Apr 5 2012 18:51:04 +00:00 cpconfig-29xx.cfg 3 3000320 Apr 5 2012 18:51:20 +00:00 cpexpress.tar 4 1038 Apr 5 2012 18:51:34 +00:00 home.shtml 5 122880 Apr 5 2012 18:51:44 +00:00 home.tar 6 1697952 Apr 5 2012 18:52:04 +00:00 securedesktop-

The show version command displays the amount of flash and RAM available on a router and switch.

To back up the running configuration to a TFTP server, use the copy running-config tftp privileged EXEC command, which can also be shortened to copy run tftp. The example that follows shows this command in action: RouterB# copy run tftp Address or name of remote host []? 192.168.0.2 Destination filename [routerb-confg]? !! 780 bytes copied in 6.900 secs (130 bytes/sec)

Answer 53 The erase startup-config privileged EXEC command, as follows, erases your router's configuration, thus bringing it back to its factory defaults: RouterB# erase startup-config Erasing the nvram filesystem will remove all files! Continue? [confirm] [OK] Erase of nvram: complete Note To complete the process, you need to reload the router. To restore a Cisco router to its factory defaults, you need to erase the startup config file and the VLAN.dat file, too.

The copy tftp running-config privileged EXEC command merges the previously backed up and running configuration into your Cisco device's RAM, so any commands not explicitly changed or removed will remain in the running configuration. Sample command output is as follows: RouterB# copy tftp running-config Address or name of remote host []? 192.168.0.2 Source filename []? routerb-confg Destination filename [running-config]? Accessing tftp://192.168.0.2/routerb-confg... Loading routerb-confg from 192.168.0.2 (via Ethernet0): ! [OK - 780/1024 bytes] 780 bytes copied in 4.12 secs (195 bytes/sec) RouterB# 01:40:46: %SYS-5-CONFIG: Configured from tftp://192.168.0.2/routerb-confg

To enter interface configuration mode, use the interface interface-id command. To enter interface mode, you first need to be in global configuration mode. The interface-id parameter is the type and number of the interface you want to configure. For example, to configure gigabit interface 0/1, enter the following: switch(config)# interface g0/1 switch(config-if)#

The hostname BuildingB-Switch global configuration mode IOS command allows you to configure this switch with a host name.

To assign the IP address to the switch, enter the following commands: interface vlan1 ip address 192.168.0.10 255.255.255.0 no shutdown Follow these steps to assign the IP address to the switch: 1. Enter the VLAN 1 interface. This is a logical interface used for management. 2. Assign the IP address and subnet masks. 3. Enable the interface by issuing the no shutdown command.

To configure the default gateway, use the ip default-gateway ip-address global configuration command. The following example configures the switch to use IP address 192.168.0.1 as its default gateway: Switch(config)# ip default-gateway 192.168.0.1 Note To remove the default gateway, use the no ip default-gateway command.

You need to configure a default gateway on the switch to allow remote networks to manage the switch. Although a switch does not see Layer 3 and above information, a default gateway is configured on a switch to allow administrators to remotely administer and configure the switch.

Assigning an IP address to a switch allows remote management of the switch.

The switch is malfunctioning. The System (SYST) LED provides a quick overall status of the switch with three states: Off: The switch is not powered on. On (green): The switch is powered on and operational. On (amber): System malfunction. One ore more power-on self-tests errors occurred and the Cisco IOS did not load.

You display the current active configuration on a switch by issuing the show running-configuration or sh run privileged command.

The show interfaces privileged command allows you to view the statistics for all interfaces configured on the switch.

The show ip interface user and privilege EXEC command displays all IP information configured for all interfaces on the switch. Following is the output of the show ip interface command: Switch# show ip interface Vlan1 is up, line protocol is down Internet address is 192.168.0.10/24 Broadcast address is 255.255.255.255 Address determined by setup command MTU is 1500 bytes Helper address is not set Directed broadcast forwarding is disabled Outgoing access list is not set Inbound access list is not set Proxy ARP is enabled

To enable a password for Telnet access, enter the line vty 0 15 global configuration command, the login command, and finally the password line subcommand. The password is case sensitive. In this example, the Telnet password is set to CCNA: Switch(config)# line vty 0 15 Switch(config-line)# login Switch(config-line)# password CCNA NOTE: Without the login command, the switch will not let you log on through Telnet, even if a password is set.

A Cisco Catalyst switch has 16 vty lines.

To restrict access to privileged EXEC mode, assign a password to privileged mode. This is done in one of two ways: by either using the enable password global command or the enable secret global command. Cisco recommends that you use the enable secret global command versus the enable password command because the enable secret command encrypts the password.

The switch will use cisco1 to enter privileged EXEC mode. When a switch has the enable password and enable secret password configured, the switch will use the enable secret password as the password to enter privileged EXEC mode.

To encrypt the passwords, use the service password-encryption global command, as follows: Switch(config)# service password-encryption

The show version switch IOS command displays the system hardware, software version, boot images, and configuration register. The following is the output of the show version command: cnat-2921-1# sh version Cisco IOS Software, C2900 Software (C2900-UNIVERSALK9-M), Version 15.1(4)M2, RELEASE SOFTWARE (fc1) Technical Support: http://www.cisco.com/techsupport Copyright (c) 1986-2011 by Cisco Systems, Inc. Compiled Mon 26-Sep-11 17:37 by prod_rel_team ROM: System Bootstrap, Version 15.0(1r)M9, RELEASE SOFTWARE (fc1) cnat-2921-1 uptime is 1 week, 5 days, 17 hours, 38 minutes System returned to ROM by power-on System restarted at 15:23:13 CST Sun Feb 10 2013 System image file is "flash0:c2900-universalk9-mz.SPA.151-4.M2.bin" Last reload type: Normal Reload Cisco CISCO2921/K9 (revision 1.0) with 2285536K/73728K bytes of memory. Processor board ID FTX1549ALHF 4 Gigabit Ethernet interfaces 2 terminal lines 1 cisco Embedded service engine(s) 1 Services Module (SM) with Services Ready Engine (SRE) Cisco SRE-V Software 2.0.1.0 in slot/sub-slot 1/0 DRAM configuration is 64 bits wide with parity enabled. 255K bytes of non-volatile configuration memory. 255744K bytes of ATA System CompactFlash 0 (Read/Write) ----------------------------------------------------------------- Technology Technology-package Technology-package Current Type Next reboot ------------------------------------------------------------------ ipbase ipbasek9 Permanent ipbasek9 security None None None uc None None None data None None None Configuration register is 0x2102

Issue the show version EXEC command to view the uptime of the switch. In addition to displaying the switch hardware configuration and software version information, the show version command displays switch uptime, switch platform information including RAM, switch serial number, and MAC address. cisco2960-1# sh version cisco2960-1 uptime is 27 weeks, 4 days, 20 hours, 4 minutes System returned to ROM by power-on

You display the MAC address table on a Catalyst 2960 by issuing the show mac-address-table privileged command, as follows: Switch-1# show mac-address-table Mac Address Table ------------------------------------------- Vlan Mac Address Type Ports ---- ----------- -------- ----- All 0000.0000.0000 STATIC CPU All 000b.469d.c900 STATIC CPU 10 0002.b3ef.c687 DYNAMIC Po1 10 0007.e980.d7a6 DYNAMIC Fa0/7 10 000d.65ac.507f DYNAMIC Po1 10 000f.207a.008c DYNAMIC Po1 10 0010.db72.b08f DYNAMIC Fa0/24 Note Static addresses are MAC addresses assigned to specific ports and not aged out. The Po1 port is a logical port used by EtherChannel. EtherChannel is discussed in ICND2.

To add a password to the console terminal line, use the line console 0 global configuration command, followed by the login and password password line configuration mode commands, as follows: Cat2960(config)# line console 0 Cat2960(config-line)# login Cat2960(config-line)# password CCNA The login subcommand forces the router to prompt for authentication. Without this command, the router will not authenticate a password. The password CCNA subcommand sets the console password to CCNA. The password set is case sensitive. Note Sometimes, when people type login, they tend to want to type login local, which looks for a username/password statement in the local router configuration. If you do not have a username and password configured locally and you type in login local, the only way to access the system would be through password recovery.

You add an MOTD banner by entering the banner motd # text # global configuration command. The pound signs (#) are delimiting characters. They can be any character of your choice, but they must be the same and cannot be included in your text. They signify the beginning and end of your text. The following example shows the banner motd command: Cat2960(config)# banner motd # Enter TEXT message. End with the character '#'. Warning only authorized users many access this switch. # Cat2960(config)# Note The MOTD banner is displayed to anyone who connects to the router through VTY, the console port, or the auxiliary port.