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What are the different terms used to describe a LAN?
VLAN, subnet or network, broadcast domain, or data link.
What devices create a LAN?
Switches and Bridges
What devices are used to separate and connect LANs?
Routers are used to separate LANs and connect LANs
What are the associated network sizes with the three different classes of IP Addresses?
- Class A: 1 - 126 (24 bits for host)
- Class B: 128 - 191 (16 bits for host)
- Class C: 192 - 223 (8 bits for host)
What are Private IP Addresses and NAT?
Private IP addresses are not routable on the public Internet. By using NAT you can use these private IP addresses on your internal networks.
What are the Private IP Address ranges for each class?
- Class A: 10.0.0.0 - 10.255.255.255
- Class B: 172.16.0 - 172.31.255.255
- Class C: 192.168.0.0 - 192.168.255.255
What is the difference between distance-vector, link state, and hybrid routing protocols?
Each technology has it's own characteristics and methods for sharing routing information between routers.
Describe properties for the different routing protocols.
- RIP and IGRP are distance vector routing protocols.
- EIGRP is a hybrid
- OSPF is a link state protocol.
- IGRP and EIGRP are Cisco proprietary, RIP and OSPF are industry standard.
What are some benefits of VLANs?
- You can achieve network adds, moves, and changes by configuring a port into the appropriate VLAN.
- You can put a group of users needing high security into a VLAN so that no users outside of the VLAN can communicate with them.
- As a logical grouping of users by function, VLANs can be considered independent from their physical or geographic locations.
- VLANs can enhance network security
- VLANs increase the number of broadcast domains while decreasing their size.
What is "Frame Tagging"?
refers to VLAN identification. This is what switches use to keep track of all those frames as they are traversing a switch fabric. It's how switches identify which frames belong to which VLAN.
What is ISL VLAN identification?
Inter-Switch Link (ISL) is what you use to explicitly tag VLAN information onto a Ethernet Frame. This tagging information allows VLANs to be multiplexed over a trunk line through an external encapsulation method, which allows the switch to identify the VLAN membership of a frame over the link. ISL is a Cisco-proprietary frame-tagging method that can only be used on Cisco switches.
What is 802.1Q VLAN identification method?
This is a non-proprietary IEEE method of frame tagging. If you are trunking between a Cisco switch link and a different brand of switch, you have to use 802.1Q for the trunk to work.
Router(config-subif)#encapsulation dot1q vlan#
What is the difference between standard and extended access lists?
- Standard access lists make decisions based on source IP address only.
- Extended access lists can look at source and destination information at Layers 3 and 4, as well as protocol type information.
What are the rules for creating and applying access lists?
Access lists are directional - you can only have one access list per direction (inbound or outbound) on an interface. The implicit deny means that any packet not matching any line of an access list will be denied; it is as if every access list ends with "deny all" function.
What is the default serial encapsulation on a Cisco router?
Cisco routers use a proprietary High-Level Data Link Control (HDLC) encapsulation on all their serial links by default.
What is the LMI in Frame Relay?
LMI is a signaling standard between a router and a frame relay switch. The LMI is responsible for managing and maintaining status between these devices. This standard also provides transmission keepalives to ensure that the PVC does not shut down because of inactivity. (Local Management Interface)
What are the different Frame Relay encapsulations?
Cisco uses 2 different Frame Relay encapsulation methods on their routers. Cisco is the the default, and it means that the router is connected to a Cisco Frame Relay switch; Internet Engineering Task Force (IETF), the second, means your router is connecting to anything but a Cisco Frame Relay switch.
What is the CIR in Frame Relay?
- CIR is the rate, in bits per second, at which the Frame Relay switch agrees to transfer data.
- (Committed Information Rate)
What are the PPP Data Link layer protocols?
The 3 Data Link layer protocols are the Network Control Protocol (NCP), which defines the Network layer protocols; the Link Control Protocol (LCP), a method of establishing, configuring, maintaining, and terminating the point-to-point connection; and the High-Level Data Link Control (HDLC), the MAC layer protocol that encapsulates the packets.
What is the result of using a hierarchical addressing scheme?
Increased number of addresses. The designers created a hierarchical addressing scheme when they created the IP address so that more addresses would be available to each network.
What is the default administrative distace for IGRP?
- IGRP's default administrative distance is 100.
- RIP's default administrative distance is 120.
What does a split horizon do?
- Ensures that information about a route will not be sent back in the direction from which the original update came.
- A split horizon will not advertise a route back to the same router from which it learned the route.
What does a poison reverse do?
- It describes when a router sets the metric for a downed link to infinity.
- A poison reverse is used to communicate to a router that the link is down and that the hop count to that network is set to infinity or unreachable.
What are the default properties used by EIGRP to calculate the best path to a destination network?
- Bandwidth & Delay
- Bandwidth and Delay are the only parameters used by default to calculate the metric of a route. Reliability and load are legitimate parameters that may also be used in the metric calculation, but they are not used by default.
What are the benefits of using a link-state routing protocol?
It uses the Hello protocol to establish adjacencies & It sends updates only when changes occur in the network.
What is LMI responsible for?
- For transmission keepalives to ensure that the PVC does not shut down because of inactivity.
- The LMI provides keepalives between the router and the frame switch to verify that the link and connection are still active.
In what mode do you configure RIP routing?
What command do you type to configure RIP?
- Global Configuration Mode
- config t
- Router RIP
- You must use classful addresses. e.g:
- network 10.0.0.0
How do you configure IRGP routing?
You must configure IRGP using the Autonomous System (AS)
- router igrp 10
- network 10.0.0.0
this example uses AS 10 meaning the router will only accept updates from AS 10.
Difference configuring EIGRP and IGRP.
Basic configuration for EIGRP is similar to IGRP; however, EIGRP has several additional features such as passive interface and summarization.
- router eigrp 20
- passive-interface serial 0/1
How do you configure a single area OSPF?
- a minimal single area configuration involves only two commands:
- Router OSPF process-id
- network x.x.x.x y.y.y.y area z
What are the steps to subnet in your head?
Understand how IP addressing and subnetting work. First, determine your block size by using the 256-subnet mask math. Then county your subnets and determine the broadcast address of each subnet- it is always the number right befor the next subnet. Your valid hosts are the numbers between the subnet address and the broadcast address.
What are the valid block sizes?
The block sizes are always 4, 8, 16, 32, 64, 128 and so on. You can determine your block size by using the 256-subnet mask math.
How do you check the value of the current configuration register setting?
- You check the current configuration register setting by using the
- SHOW VERSION
What are the various configuration register commands and settings?
The 0x2102 setting is the default on all Cisco routers and tells the router to look in NVRAM for the boot sequence. 0x2101 tells the router to boot from ROM, and 0x2142 tells the router not to load the startup-config in NVRAM to provide password recovery.
How do you check a switch port's VLAN assignment when you are plugging in a new host?
If you plug a new host into a switch, then you must verify the VLAN membership of that port. If the membership is different than what is needed for that host, the host will not be able to reach the needed network services.
Besides assigning a port to a VLAN, what is involved in VLAN configuration?
Trunk links must be considered and configured, as well as VTP configurations on individual switches.
- sample commands:
- R(config)#vtp mode client
- R(config)#vtp domain domainnameR(config)#int fa0/2
- R(config-if)#switchport access VLAN2
What are the 3 types of Ethernet cabling and when you would use them?
The 3 types of cables that can be created from an Ethernet cable are
- straight-through (to connect a PC or a router's Ethernet Interface to a hub or switch)
- crossover (to connect hub to hub, hub to switch, switch to switch, or PC to PC)
- rolled (for a console connection from a PC to a router or switch)
How do you connect a console cable from a PC to a router?
- Take a rolled cable and connect it from the COM port of the host to the console port of a router.
- Start HyperTerminal and set the bits per second (bps) to 9600 and flow control to None.
How do you determine which switch will be the root bridge?
Assuming the priority is equal, the switch with the lowest MAC address will become the root bridge.
How do you back up and IOS image?
By using the priviledged-mode command
copy flash tftfp
you can back up a file from a flash memory to a TFTP (network) host.
How do you restore or upgrade an IOS image?
By using the priviledged-mode command
copy tftp flash
you can restore or upgrade a file from a TFTP (network) server to flash memory.
How do you prepare to back up an IOS image to a network server?
In order to back up an IOS image to a network server, you must first make sure you can access the network server, ensure the network server has adequate space for the code image, and verify the file naming and path requirements.
How do you save a router configuration?
There are a couple of ways to save the configuration of a router, but the most common, as well as the most tested, method is
copy running-config startup-config
How do you erase the configuration of a router?
To erase the configuration of a router, type the priviledged-mode command
and reload the router.
What are the sequence of steps when you power on a router?
When you first bring up a Cisco router, it will run a power-on self test (POST), and if that passes, it will then look for and load the Cisco IOS from Flash memory, if a file is present. The IOS then proceeds to load and look for a valid configuration in NVRAM called the startup-config. If no file is present in NVRAM, the router will go into setup mode.
What does Setup mode provide?
Setup mode automatically starts if a router boots and no startup-config is in NVRAM. You can also bring up setup mode by typing setup from the priviledged mode. Setup provides a minimum amount of configuration in an easy format for someone who does not understand how to configure a Cisco router from the command line.
What is the difference between user mode and priviledged mode?
- User mode provides command-line interface with very few available commands by default. User mode does not allow the configuration to be viewed or changed.
- Privileged mode allows a user to both view and change the configuration of a router. You can enter privileged mode by typing the command enable and entering the enable password or enable secret password, if set.
What information does the show version provide?
The show version command provides basic configuration for the system hardware as well as the software version, the names and sources of configuration filess, and the boot images.
How do you set the hostname of a Router?
The command sequence to set a hostname is as follows:
- config t
- hostname hostname
What is the difference between the enable password and enable secret password?
Both of these passwords are used to gain access to priviledged mode; however, the enable secret is newer and encrypted by default. Also, if you set the enable password and then set the enable secret, only the enable secret will be used.
How do you set the enable secret on a router?
To set the enable secret, you use the command enable secret. Do not use enable secret password password,
or you will set your password to "password password". Commands are:
- config terminal
- enable secret secretpassword
How do you set the console password on a router?
To set the console password on a router, use the following commands:
- configure terminal
- line console 0
- password consolepassword
How do you set the Telnet password on a router?
To set the Telnet password on a router, use the following commands:
- config t
- line vty 0 4
- password telnetpassword
How do you troubleshoot a serial link?
If you type show interface serial 0 and see that it is "down, line protocol is down", this will be considered a Physical layer problem. If you see it as "up, line protocol is down", then you have a Data Link layer problem.
How do you set up and IP address and default gateway on the 1900?
- Router#config t
- Router(config)#ip address 172.16.10.15 255.255.255.0
- Router(config)#ip default-gateway 172.16.10.1
How do you set up an IP address and default gateway on the 2950?
- R#config t
- R(config)#int vlan1
- R(config-if)#ip address 172.16.10.17 255.255.255.0
- R(config-if)#no shut
- R(config)#ip default-gateway 172.16.10.1
How do you erase the configuration file on a 1900?
How do you erase the configuration file on the 2950?
Explain the standard IP access list configuration command.
- To configure a standard IP access list, use the access-list numbers 1-99 or 1300-1999 in global configuration mode.
- Choose permit or deny, then choose the source IP address you want to filter on using either (host, network, or wildcard masking)
Explain the extended IP access list configuration command.
- To configure an extended IP access list, use the access-list numbers 100-199 or 2000-2699 in global configuration mode.
- Choose permit or deny, the Network layer protocol, the source IP address you want to filter on, the destination address you want to filter on, and finally the Transport layer protocol (if selected).
What commands are used for PPP encapsulation?
You can use the encapsulation PPP command on a serial interface to change from HDLC to PPP encapsulation. Also, you can further configure authentication using the ppp authentication command.
What commands are used for Frame Relay encapsulation?
You can use the encapsulation frame-relay command on a serial interface to change the encapsulation to Frame Relay. Additionally, you will need to configure DLCI information, LMI and encapsulation types if they will differ from the default, and potentially subinterfaces if you will have multiple PVCs per physical interface.
What are the 5 basic dialer map steps for configuring DDR?
- 1. Dialer
- 2. Map
- 3. Protocol
- 4. Next hop
- 5. Dial string
What commands implement EIGRP on a router?
router eigrp as
What command will show you whether a DTE or DCE cable is plugged into Serial 0?
show controllers Serial 0
What are the 2 valid PPP authentication methods?
PAP and CHAP are valid authentication methods available to PPP authentication.
What type of approach is the OSI model?
OSI is a LAYERED approach. Functions are divided into layers, and the layers are bound together. This allows layers to operate transparently to each other, that is changes in one layer should not impact other layers.
What are the steps to data encapsulation?
User information is encapsulated to data, data to segments, segments to packets or datagrams, packets or datagrams to frames, and frames to bits.
What command is used to find which VLANs are configured on a switch?
Use the show vlan command on the Catalyst 1900 to see the configured VLANs, or use the same command on the Catalyst 2950 to examine the contents of the VLAN database.
Name some implementations of VTP
Changes to VLAN configurations can propogate between switches; your VTP mode must be transparent if you do not want your switches to participate in VTP.
How do you verify RIP routing
show ip route provides you with the contents of the routing table. An R on the left side of the table indicates a RIP found route. The debug ip rip command shows you RIP updates being sent and received on your router. If you see a route with a metric of 16, that route is considered down.
How do you verify IRGP routing?
show ip route shows you the routing table, and an I on the left side of the table indicates and IGRP found route. The [100/123456] indicates the administrative distance - 100 is for IGRP, the composite metric. The composite metric is determined by bandwidth and delay of the line, by default.
How do you verify EIGRP operation?
- You can verify EIGRP operation using the commands
- show ip eigrp neighbor and show eigrp topology
How do you verify operation of OSPF?
- There are many show commands that provide useful detail on OSPF. You should be completely familiar with the output of each of the following:
- show ip ospf, show ip ospf database, show ip ospf interface, show ip ospf neighbor, and show ip protocols
When would you use the ping command?
Packet Internet Groper (PING) uses ICMP echo requests and ICMP echo replies to verify an active IP address on a network.
What Router mode can send a ping?
You can ping an IP address from a router's user mode or priviledged mode, but NOT from configuration mode.
When would you use CDP?
Cisco Discovery Protocol can be used to help you document and troubleshoot your network.
What is the output from the show cdp neighbors command?
show cdp neighbors command provides the following information: device ID, local interface, holdtime, capability, platform, and port ID
During Telnet, how do you keep your connection, but return to the originating console?
- If you want to keep your connection to a remote device but still come back to your original router console, you can press the CTRL+SHIFT+6 key combination, release it, and then press X.
- If you telnet to a router or swith, you can end the connection by typing exit at any time.
What command will verify your Telnet sessions?
show sessions will provide you with all the sessions your router has to other routers.
How do you build a static host table on a router?
- By using the global configuration mode command
- ip host host_name ip_addressyou can build a static host table on your router.
How do you verify your host table on a router?
- You can verify the host table with
- show hostscommand
What command is used to verify an access list on an interface?
- To see whether an access list is set on an interface and in which direction it is filtering, use the show ip interface command.
- This command will not show you the contents of the access list, merely which access lists are applied on the interface.
What command is used to verify the access list configuration?
To see the configured access lists on your router, use the show access-list command. This command will not show you which interfaces have an access list set.
What commands are used to troubleshoot Frame Relay?
The show frame relay lmi command will give you the LMI traffic statistics exchanged between the local router and the Frame Relay switch. The show frame pvc command will list all configured PVCs and DLCI numbers.
What commands are used for troubleshooting PPP and ISDN?
In addition to standard show interface and IP troubleshooting tools, there are debug and show commands specific to each technology.
Protocol data units (PDU) at the Network layer of the OSI are called what?
Segmentation of a data stream happens at which layer of the OSI model?
- Transport layer.
- The transport layer receives large data streams from the upper layers and breaks them up into smaller pieces called segments.
What command will show you the hostname resolved to the IP address on a router?
- show hosts
- The command to see the host table, which resolves hostnames to IP addresses, is show host or show hosts.
What router command allows you to determine whether an IP access list is enabled on a particular interface?
The show ip interface command tells you which ports have access lists applied.
What command can you use to list all configured PVCs and DLCIs?
show frame-relay pvc command will show the PVCs configured and the associated DLCI numbers.
What are the 3 layers in the Cisco 3-layered model?
Core, Distribution, & Access layers.
What are the Seven layers of the OSI model?
- APPLICATION - Application services
- PRESENTATION - encryption, compression, translation services.
- SESSION - dialog control
- TRANSPORT - end-to-end connection
- NETWORK - routing
- DATA LINK - framing
- PHYSICAL - physical topology
Which layer of the OSI model provides segmentation, sequencing, and virtual circuits?
Transport Layer provides segmentation, sequencing, and virtual circuits.
Which layer of the OSI model provides framing and places data on the network medium?
The Data Link layer provides framing and places data on the network medium.
What is the difference between connection-oriented and connectionless network services?
Connection-oriented uses acknowledgements and flow control to create a reliable session. More overhead is used than in a connectionless network service. Connectionless services are used to send data with no acknowledgements or flow control. This is considered unreliable.
What are the 5 states of Spanning Tree Protocol?
- The purpose of BLOCKING state is to prevent the use of looped paths.
- A port in LISTENING state prepares to forward data frames without populating the MAC address table.
- A port in LEARNING state populates the MAC address table but doesn't forward data frames.
- The FORWARDING port sends and receives all data frames on the bridged port. Lastly a port in the DISABLED state is virtually disabled.
What is the main purpose of STP in a switched LAN?
the main purpose of Spanning Tree Protocol (STP) is to prevent switching loops in a network with redundant switched paths.
What are the 4 Ethernet frame types and the differences between them?
- Ethernet_II: has a type field.
- 802.3: has a length field
- 802.2: has DSAPs and SSAPs
- SNAP: has it's own protocol field.
How does the cut-through LAN switch method work?
When the switch is in cut-through mode, it waits only for the destination hardware address to be received before it looks up the address in the MAC filter table.
What are the 3 LAN Switch methods and their functions?
- Cut-Through, Fragment Free, & Store-and-Forward.
- store-and-forward offers error checking; cut through and Fragment Free offer lower latency.
How does Fragment Free LAN Switching method work?
The Fragment Free LAN switch method checks the first 64 bytes of a frame before forwarding it for fragmentation.
How does the Store-and-Forward LAN Switching method work?
Store-and-Forward first receives the complete data frame on the switch's buttfer, then a CRC is run, and then the switch looks up the destination address in the MAC filter table.
Explain the basic IP routing process.
The frame changes at each hop, but the packet is never changed or manipulated in any way until it reaches the destination device.
Name some Process/Application layer protocols.
Telnet is a terminal emulation protocol and it allows you to log into a remote host and run programs. FTP is a connection-oriented service that allows you to transfer files. TFTP is a connectionless file transfer program. SMTP is a send mail program.
Name some Host-to-Host layer protocols
Transmission Control Protocol (TCP) is a connection-oriented protocol that provides reliable network service by using acknowledgements and flow control. User Datagram Protocol (UDP) is a connectionless protocol that provides low overhead and is considered unreliable.
Name some Internet layer protocols.
Internet Protocol (IP) is a connectionless protocol that provides network address and routing through an internetwork. Address Resolution Protocol (ARP) finds a hardware address from a known IP address. Reverse ARP (RARP) finds an IP address from a known hardware address. ICMP provides diagnostics and unreachable messages.
What are the 4 types of memory on a Cisco router?
- RAM - Random Access Memory. Used to hold ARP cache, routing tables, and running-config.
- ROM - used to start and maintain the router.
- NVRAM - used to hold the router and switch configuration. NVRAM is not erased when the router or switch is reloaded.
- FLASH - holds the Cisco IOS. Not erased when the router is reloaded. It is an EEPROM created by Intel.
What is the configuration register?
Used to control how the router boots up. This value can be seen with the show version command and typically is 0x2102, which tells the router to load the IOS from flash memory
What is the relationship between access lists and packet control?
Access lists can be used to filter or drop packets in order to control who has access to resources such as VTY, or to determine what networks are advertised by dynamic routing protocols.
What is the meaning behind "Implicit Deny"?
At the end of every access list is an implicit deny. What this means is that if a packet does not match any of the lines in the access list, then it will be discarded. Also, if you have nothing but deny statements in your list, then the list will not permit any packets.
What is the difference between Leased Lines, Circuit Switching, and Packet Switching?
A leased line is a dedicated connection, a circuit-switched connection is like a phone call and can be on or off, and packet switching is essentially a connection that looks like a leased line but is priced more like a circuit-switched connection.
What are the 3 primary WAN protocols?
- The 3 primary WAN protocols are HDLC, Frame Relay, and PPP. Others include LAPB (Link Access Procedure Balanced) & ATM (Asynchronous Transfer Mode).
- HDLC (High-Level Data Link Control) is the default encapsulation on Cisco routers.
- PPP (Point-to-Point Protocol) provides an industry-standard way of encapsulating multiple routed protocols across a link and must be used when connecting equipment from different vendors.
- Frame Relay is a packet-switched technology that can offer cost advantages over leased lines but has more complex configuration options.
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