Albert’s CCNA Study Guide(2)
添加时间: 2007-9-8 2:59:32 作者: Cisco认证考试 阅读次数:50 来源: http://www.d9soft.com
ET:Exchange Termination: This is the local phone company's logical connection from your telephones to the phone network
ISDN Network Termination Devices Intermediate Devices
NT1: Treated as customer premises equipment (CPE)
NT2: Typically found in digital private branch exchanges (PBXs). At the layer2 and layer3
NT1/2: combined functions of NT1 and NT2
ISDN Reference Point
R: It is between non-ISDN equipment and a TA
S: It is between user terminals and an NT2
T: It is between NT1 and NT2
U: It is between NT1 devices and line termination equipment in a carrier network.
Customer Premise Equipment
Are devices physically located on the subscriber's premise: Such as telephones and modems.
Demarc
The demarcation point is the junction at which the CPE ends and the local loop portion of the service begins.
DTE and DCE
The WAN physical layer describes the interface between the data terminal equipment DTE and the data circuit terminating equipment DCE. Typically the DCE is the service provider, and the DTE is the attached device.
DTE
Data terminal equipment: Device at the user end of a user network interfaces that serves as a data source, destination or both and connects through a DCE device.
CO Central Office:
Local telephone company office to which all-local loops in a given area connect and in which circuit switching of subscriber.
LMI Local Management Interface:
A signaling standard between the CPE device and FR switch that is responsible for managing the connection and maintaining status between the devices
PAP and CHAP
Router> EXEC Mode
Router# Privileged EXEC Mode
> or rommon > ROM Monitor Mode
Router RXBoot Mode
Router (config)# Global Configuration Mode
Router (config-mode)# Other Configuration Modes
Add RIP to the Router
Router(config-if)# router RIP
The second command specifies which networks to receive rip updates from
Name# network x.x.x.x
Add IGRP protocol to Router
Router(config)# router igrp groupnumber
Router(config)#
Add IPX Routing
Type IPX routing
Task
Command
Diagnose basic network connectivity (user level)
Ping ipx
Diagnose basic network connectivity (privilegedlevel)
Ping [ipx]
Display status of the IPX interface configured in the router and the parameters configured on each interface.
Show ipx interface
List the enteries in the IPX routing table
Show ipx servers
Display information about the number and type of ipx packets transmitted and received.
Show ipx traffic
Help Command
If you don’t know the command for a particular command like clock you type clo? It will finish it for you.
If you don’t know the command then type (?) it must have a space after the word.
To list keywords or arguments, parameters enter a question mark (?) in place of a keyword or argument.
Complete a partial command name. abbreviated-command-entry
List all commands available for a particular command mode. ?
List a command’s associated keywords. command ?
List a keyword’s associated arguments. Command keyword ?
RAM/DRAM: Working storage and contains the dynamic configuration information.
NVRAM: Contains backup copy of your configuration.
Flash memory: Erasable, programmable read only memory. Contains Cisco IOS software.
ROM: Contains an initializing bootstrap program.
- If no configuration file exists, the router will revert to setup mode.
EXEC Mode:
Has two levels User mode and privileged mode
User mode checks the status of router status
Privileged mode: Includes those that change the router configuration
To enter privileged mode type enable
To exit user EXEC mode type logout at the prompt
Global configuration mode
Type configure command at the privileged EXEC mode prompt. To end it use CTRL-Z, end, and exit
Global Configuration mode:
To configure a router it must use the host name of the router.
TAB Will complete the command for you.
Ctrl Move to the beginning of the command line
Ctrl
or UP arrow and show history is Previous command recall
Ctrl or Down arrow is Most recent recall
Show running-config: Displays the active configuration parameters.
Show startup-config: Displays the backup configuration file.
Show ip route: Displays the entries in the routing table.
Copy tftp-running config - copies a file from a tftp server to RAM
Copy tftp startup config - loads a configuration file from a tftp server directly into RAM
Copy startup config running config: Copies the configuration information in NVRAM to RAM
debug ipx routing activity: To monitor IPX RIP updates sent and received
Line console 0: command establishes a login password on the console terminal.
Line vty 0 4: command establishes a login password on incoming Telnet sessions.
Test question actually both
Set DCE clock rate Router (config-if)#clock rate 56000
Set bandwidth Router (config-if)#bandwidth 56
SHOW FLASH: you get the following
- Total amount of memory on your router
- Amount of memory available
- Name of the system image file
ARP
Is used to resolve or map IP address to a MAC sublayer address
ARP determines the data link layer address for unknown IP addresses.
RARP
Doesn't know its IP Address but does know it MAC address.
Uses Broadcasts to determines the network addresses when data link layer addresses are known. On a local segment, RARP can be used to initiate a remote operating system load system. MAC to IP
Inverse ARP
It can be used to in which LMI can resolve an IP address from a DLCI number. Used to request the next hop protocol address for a specific connection.
TCP
Breaks and reassembles messages into datagrams
Uses sequence numbers and windowing
Sends acknowledgements
Provides control and error checking
ICMP
It redirects which occur when a router determines the next hop is on the same network the packet originated from. Unreachable messages are returned when a service or host is not available
IP, UDP, IPX
Provides connectionless transmission
UDP
Uses no Windowing or acknowledgements and is connectionless
Cisco 7000 and 7200 series routers by slot and port numbers
Cisco 7000 and 7500 series routers with VIP cards by slot, port adapters, and port numbers.
To quit the interface configuration mode, type exit at the system prompt.
Encapsulation
SO?/span> HDLC
S1?/span>HDLC
E1?/span> Novell ether
9e?/span> Network number assigned to interface E0
6c?/span> Assigns a secondary network number to interface E0
NCP Network Control Protocol:
Carries packets from several protocols across a link
Provides clients with access to server resources. EX file access, printing, synchronization, and security. A Network Control Protocol frame in a Point-to-Point Protocol is used for selecting and configuring the network layer protocol.
Link Control Protocol (LCP)
Is used by PPP provides a method to negotiate and setup control options and of establishing, configuring, maintaining and terminating the point-to-point connection. It also used to test data link connection.
PPP Point To Point: Uses its NCP Network Control Program Host to network connections over synchronous and asynchronous circuits
PPP Encapsulation: requires a password and error corrections used by IP, IPX, and Appletalk
PAP:Is not a strong authentication program. Requires a password and error corrections. PAP provides a simple method for a remote node to establish its identity using a two-way handshake.
Stacker: Compresses data at source
Predictor: Reproduce data at destination
CHAP: Is used at the startup of a link, and periodically to verify the identity of the remote node using a three-way handshake. Perform
Challenge Handshake provides protection against playback attack through the use of a variable challenge value that is unique and predictable
SVC Switched Virtual Circuit
Only exists for the duration of the session.
- Call Setup
- Information transfer
- Call clear
Class A - 1-127 / 8 bits
Class B - 128-191 / 16 bits
Class C - 192-223 / 24 bits
Class D - 224 multicast
AABB0001.00001B03ACC33.0452
AABB0001 is the network number
00001B03ACC33 is the node address
0452 is the socket number
Destination 10.4.0.6 = Network layer header
Source 00.00.OB. A4.26.39 Data link header
Destination port 20 Transport layer header
0.0.8.64 is the host number
Fragmentation:
Is a process that occurs on a router somewhere between the source and destination? This process segments the datagrams into a convenient size into a single frame for transport over the network.
Poison Reverse
Poison reverse updates are sent to remove a route and to place it in holddown.
Holddowns
Are used to prevent regular update messages from inappropriately reinstating a route that may have gone bad. It prevents temporary routing loops while convergence takes place. A newly learned route is used until the holddown time expires.
Split Horizon
Derive from the fact that it is not useful to send information about a route back in the direction from which it came.
Cut Through
LAN switch copies only the destination address into its onboard buffers. A cut through switch provides reduced latency because it begins to forward the frame as soon as it reads the destination address and determines the out going interface.
Store and Forward:
Has a variable delay because of packet size and waits for the packet to be fully received before forwarding it. It copies the entire frame into its onboard buffers and computes the cyclic redundancy check CRC
IGRP Metric includes:
Bandwidth, Delay, Reliability, Loading, MTU
Interface ethernet 0.1 (Indicates the first subinterface on interface E0)
Interface ethernet 0.2 (indicates the second subinterface on interface E0)
Dialer list is used to filter what traffic is interesting
PRI circuit types:
E1 uses CRC4 or no CRC4
T1 uses SF or ESF
Three basic methods used in networking
Buffering: Buffering is used by network devices to temporarily store bursts of excess data in memory until they can be processed. Occasional data bursts are easily handled by buffering. However, excess data bursts can exhaust memory, forcing the device to discard any additional datagrams that arrive.
Source Quench: Source quench messages are used by receiving devices to help prevent their buffers from overflowing. The receiving device sends source quench messages to request that the source reduce its current rate of data transmission
Sliding Window: Method of flow control in which a receiver gives transmitter permission to transmit data until a window is full. When the window is full, the transmitter must stop transmitting until the receiver advertises a larger window.
Pacing: Technique for ensuring that a transmitting entity, such as a modem, does not overwhelm a receiving entity with data.
Advantages of LAN Segments
- Decrease broadcasts, and groups of computers based on geographical together.
- You can divide a network into smaller segments to reduce the number of users per segment, thereby increasing the bandwidth available to each user in the segment.
- Bridges segment LANS by MAC address.They don’t need upper layer knowledge. Are necessary for Netbios and SNA
- Switches are used at wire speed without introducing latency and congestion. Are directed to the path between switch ports.
LAN Segmentation using routers
A router between LANS
LAN Segmentation using Switches
Are highly intelligent bridged segments, with a few other interesting features such as VLANS, and lots of protocols for tunneling data between switches? Switches provide the same functionality as bridges except they do it at wire speed (without introducing latency).
LAN Segmentation using bridges
Bridges segment by using MAC addresses
Identify at least 3 reasons why the industry uses a layered model.
Lower layers not dependant on upper layers.
Gives media independence
Allows networks to work without concern for what type of media or topology they running on.
You can have a maximum number of 6 name servers.
Spanning Tree
- Defined as a loop free subset of a network topology.
- Bridges use the spanning tree algorithm, enabling a learning bridge to dynamically work around loops in a network topology by creating a spanning tree.
- Learning bridges is a bridge that performs MAC address learning to reduce traffic on the network.
Spanning-Tree Protocol is a link management protocol that provides path redundancy while preventing undesirable loops in the network. For an Ethernet network to function properly, only one active path can exist between two stations. Multiple active paths between stations cause loops in the network. If a loop exists in the network topology, the potential exists for duplication of messages. When loops occur, some switches see stations appear on both sides of the switch. This condition confuses the forwarding algorithm and allows duplicate frames to be forwarded.
To provide path redundancy, Spanning-Tree Protocol defines a tree that spans all switches in an extended network. Spanning-Tree Protocol forces certain redundant data paths into a standby (blocked) state. If one network segment in the Spanning-Tree Protocol becomes unreachable, or if Spanning-Tree Protocol costs change, the spanning-tree algorithm reconfigures the spanning-tree topology and reestablishes the link by activating the standby path.
Spanning-Tree Protocol operation is transparent to end stations, which are unaware whether they are connected to a single LAN segment or a switched LAN of multiple segments.
VLANS
- A logical network
- A broadcast domain
- They are created by location, function, group, and department.
- Through a switch is designed to segment a LAN into individual collision domains, the collision domains still belong to the same broadcast domain. The broadcast traffic from a collision domain is forward to all collision domains in the allowing devices within the broadcast domain to communicate with one another.
- Done with a switch using Frame-Tagging (can be used between switches if you have ISL inter-switch link) Frame-Tagging uses unique user-defined identifiers while within the switch fabric, and is very scalable.
VLANS provide the following benefits:
Reduced Administration Costs.
Controlling Broadcast Activity
Better Network Security
Leveraging Existing LAN Hub Investments
X.25
Offers simultaneous service to many hosts.
Defines how connections between DTE and DCE are maintained for remote terminal access and computer communications in PDNs. X.25 specifies LAPD, a data link layer protocol, and PLP, a network layer protocol. Frame Relay has to some degree superseded X.25
Frame Relay
Uses permanent virtual circuit identifiers and uses simplified framing with no error correction mechanisms. At layer 2 which is at the data link layer.
SDLC Synchronous Data Link Control:
Circuit or packet-switched networks
Bounded or unbounded media, half or full duplex
Point-to-point or multipoint
2 node types. Primay or Secondary (controlled by primary)
It is a data link layer protocol that manages communication and packet framing between DTE and DCE devices.
LAPD is a bit oriented protocol that ensures that frames are correctly ordered and error free.
HDLC High Level Data Link Control:
Default serial encapsulation
Supports both point-to-point and multipoint configurations.
LAPB Link Access Procedure Balanced:
Makes sure frames are error free and sequenced
At layer 2 provide reliability and sliding windows. LAPB provides a confirmed data service between two points. Primarily used with X.25 but can also be used as a simple data link transport.
Windowing:
A technique that controls the amount of information sent end to end and that specifies the amount information to have outstanding.
- The window size = 3 is more efficient test question
IPX Maximum-Paths
Configures load sharing over equal metric paths. Load sharing occurs when parallel metric paths are available between the source and directly connected networks leading to the destination. The default value of number of path is 1, which means load balance is disabled by default.
Autonomous System:
A set of routers under common administration.
Administrative Distance:
A rating of trustworthiness of a routing information source, which is 0 that is the best.
0x0 must boot thee operating system manually with the boot command
0x1 will cause the router to automatically boot from ROM
0x2 Examine NVRAM for boot system and configuration register boot field
0x4to boot IOS from a network server
SAP packets maybe one of these types:
0x1 General query
0x2 General response
0x3 Get Nearest Server request
0x4 Get Nearest Server response
FECN Forward Explicit Congestion Notification:
When Frame Relay switch recognizes congestion in the network, it sets the FECN bit in a frame relay packet bound for the destination device, indicating that congestion has occurred for the destination device, indicating that congestion has occurred from source to destination.
BECN Backward explicit Congestion Notification:
When Frame Relay switch recognizes congestion in the network, it sets the BECN bit to the source router instructing the router to reduce the rate at which it is sending packets.
CDP Cisco Discovery Protocol:
Provides a single proprietary command that enables network administrators to access a summary of the multiple protocols and address configured on other directly connected routers.
Half Duplex
The circuits are receive RX transmit TX and collision detection. When half duplex Ethernet is implemented, TX circuit is active at the transmitting station. When another station is transmitting, the station's RX circuit is active. Logically, these circuits feed into a single cable creating a situation similar to the narrow one bridge analogy.
Full Duplex
Uses only point-to point connections
Allows simultaneous transmission and reception of packets on two pair of wires.
Convergence:
Routers have a consistent view of an internetwork topology
Startup sequence
Bootstrap from Rom
Cisco IOS from Flash
From tftp
From Rom
Configuration File from NVRAM
From tftp server
From console
Configuring Access List:
If it has a -if then it is for an interface
Like (config-if) it is makes it an interface
If is just plain then it just Global
Like (config)
Beacon Frame:
When a node determines that no tokens have been received from its NAUN, it initiate a beacon frame to notify the ring of an open cable.
上一篇文章: Albert’s CCNA Study Guide(1) 下一篇文章: CCNP-BCRAN(1)
相关文章: