Semester 2 Network (Journal)
Some ISPs provide technical support and consulting services for an additional fee.
Internet-internetwork that connects networks worldwide. The internet evolved in part from ARPANET. Internet is an abbreviation for internetwork.
E-commerce-electronic ommerce.Buying and selling goods and services on the internet.
Communications-Refers to any electronic method of communication,such as use of email,instant messaging and internet using IP phones and Voice over (VoIP)technology to reduce phone costs.
Internet standard-is a rules that determines how something must be done.
ISP-Internet service Provider.Organization, such as the local phone or cable company, that providers internet service to home users. An ISP is a company or organization through which a subscriber obtains Internet access.
Equipment co-location-A business may option to have some or all internal network equipment physically located on the ISP premises.
*Web hosting-The ISP provides the server and application software for storing web pages and web content for the business website.
*FTP-The ISP provides the server and application software for the FTP site of a business.
FTP-File Transfer Protocol-Application standard used for transferring files between network nodes.FTP is defined in RFC 959 and is part of the TCP/IP protocol stack.
*Applications and media hosting - The ISP provides the server and software to allow a business to provide streaming media such as music, video, or applications such as online databases.
Stream-Continuous transmission of data from one location to another. Streaming video is the continuous , real-time flow of the video being downloaded .
*Voice over IP - A business can save on long distance telephone charges, especially for internal calls between geographically distant offices, by using Voice over IP (VoIP).
*Technical support - Many businesses do not have the in-house technical expertise to manage large internal networks. Some ISPs provide technical support and consulting services for an additional fee.
Bandwidth is measured in bits per second (bps). Higher bandwidth speeds are measured in kilobits per second (kbps), megabits per second (Mbps), or gigabits per second (Gbps).
Private peer-Direct connection between two or more ISPs that allows them to switch internet to switch internet traffic at no cost.
The Internet backbone is provides high-speed data links to interconnect the POPs and IXPs in major metropolitan areas around the world.
The ping command tests the accessibility of a specific IP address. The ping command sends an ICMP (Internet Control Message Protocol) echo request packet to the destination address and then waits for an echo reply packet to return from that host.
ICMP is an Internet protocol that is used to verify communications.
Scalability is the capacity of a network to allow for future change and growth. Scalable networks can expand quickly to support new users and applications without affecting the performance of the service being delivered to existing users.
Customer Service receives the order from the customer and ensures that the specified requirements of the customer are accurately entered into the order tracking database.
Planning and Provisioning determines whether the new customer has existing network hardware and circuits and if new circuits need to be installed.
The On-site Installation is advised of which circuits and equipment to use and then installs them at the customer site.
Network Operations Center (NOC) monitors and tests the new connection and ensures that it is performing properly.
The Help Desk is notified by the NOC when the circuit is ready for operation and then contacts the customer to guide them through the process of setting up passwords and other necessary account information.
An Internet standard is the end result of a comprehensive cycle of discussion, problem solving, and testing. When a new standard is proposed, each stage of the development and approval process is recorded in a numbered Request for Comments (RFC) document so that the evolution of the standard is tracked.
The Internet has a hierarchical structure. At the top of this hierarchy are the ISP organizations.
ISP help desk technicians provide solutions to customer problems with the goal of network optimization and customer retention. A good help desk team ensures that problems are resolved quickly and to the satisfaction of the customer.
ISP, there are usually three levels of customer support:
Level 1 is for immediate support handled by junior-level help desk technicians.
Level 2 handles calls that are escalated to more experienced telephone support.
Level 3 is for calls that cannot be resolved by phone support and require a visit by an on-site technician.
Managed service-service provider that offers onsite support of a customer network.
SLA-service level Agreement(contract that defines expectations between an organization and the service vendor to provide an agreed upon level of support.
Incident management-Procedure that should be followed when a help desk technician initiates a problem solving process.
Preparation; courteous greeting ; open a trouble ticket ; listen to the customer ; Adapt to customer temperament; diagnose a simple problem correctly; log the call;
In a similar manner, the OSI model can be used as a means to focus on a layer when troubleshooting to identify and resolve network problems.
Application layer-*defines interfaces between application software and network communication functions.*provides standardized services such as file transfer between systems.
Presentation layer -*Standarsizes user data formats for use between different types of systems.*Encodes and decodes user data; encrypts and decrypts data; compresses and decompresses.
Session layer-*Manages user sessions and dialogues *Manages links between applications .
Transport layer -*Manages end -to end message delivery over the network.*can provide reliable and sequential packet delivery through error recovery and flow control mechanisms.
Network layer-*provides logical network addressing .*router packet between networks based on logical addressing.
Data link layer-*defines procedures for operating the communication links.*detects and corrects frame transmit errors.*adds physical addresses to frame.
Physical layer -defines physical means of sending data over network devices.*interfaces between network medium and devices.*defines optical, electrical, and wireless media.
*includes all forms of electromagnetic transmission such as light .electricity, infrared and radio waves.
Bottom-Up - The bottom-up approach starts with the physical components of the network and works its way up the layers of the OSI model. Bottom-up troubleshooting is an effective and efficient approach for suspected physical problems.
Top-Down - The top-down approach starts with the user application and works its way down the layers of the OSI model. This approach starts with the assumption that the problem is with the application and not the network infrastructure.
Divide-and-Conquer - The divide-and-conquer approach is generally used by more experienced network technicians. The technician makes an educated guess targeting the problem layer and then based on the observed results, moves up or down the OSI layers.
tracert - Determines if the routing path between the source and destination is available
link-local address will be automatically assigned to the local host by the operating system. IPv4 addresses in the address block 169.254.0.1 to 169.254.255.254 (169.254.0.0 /16) are designated as link-local addresses. A link-local process will randomly select an IP address within the 169.254.0.0/16 range. But what prevents two hosts from randomly selecting the same IP address?
UDP-user datagram protocol-connectionless transport layer protocol in the TCP/IP protocol stack.UDP is a simple protocol that exchanges datagram's without acknowledgements or guaranteed delivery. It is a connectionless service for delivery of data with less overhead than TCPand designed for speed .
The TCP/IP stack can be tested and verified using a loopback address. The loopback is a special address, the reserved IPv4 address 127.0.0.1, which hosts use to direct traffic to themselves
A physical topology is the actual physical location of cables, computers, and other peripherals. A logical topology documents the path that data takes through the network and where network functions, like routing, occur.
Logical topology-map of the devices and flow of data on a network. A logical topology demonstrates how the devices communicate with each other. Compare logical topology with physical topology.
With a star topology, each device is connected via a single connection to a central point. The central point is typically a switch or a wireless access point. The advantage of a star topology is that if a single connecting device fails, only that device is affected. However, if the central device, such as the switch, fails, then all connecting devices lose connectivity.
An extended star is created when the central device in one star is connected to a central device of another star, such as when multiple switches are interconnected, or daisy-chained together.
Mesh Topologies-Most Core Layers in a network are wired in either a full mesh or a partial mesh topology. In a full mesh topology, every device has a connection to every other device. While full mesh topologies provide the benefit of a fully redundant network, they can be difficult to wire and manage and are more costly.
For larger installations, a modified partial mesh topology is used. In a partial mesh topology, each device is connected to at least two other devices. This arrangement creates sufficient redundancy, without the complexity of a full mesh.
SWOT-(strengths,weaknesse>s,opportunities,or threats)part of the planning process in network design that evaluates the strengths,weaknesses,oppo
Telecommunications room- or wiring closet, in a small, single-floor network is usually referred to as the Main Distribution Facility (MDF).Facility that maintains network and telecommunications equipment, vertical and horizontal cable terminations, and cross-connect cables. A telecommunications room is also known as riser, a distribution facility, or a wiring closet. telecommunications room is critical to the security and reliability of the network.
MDF-(main Distribution Facility) primary communications room for a building. An MDF is the central point of a star networking topology where patch panels, hubs, and routers are located. It is used to connect public or private lines coming into the building to internet networks.
Intermediate Distribution Facilities (IDFs). IDFs are typically smaller than the MDF, and connect to the MDF.
ISO standards refer to MDFs and IDFs using different terminology. MDFs and IDFs can also be referred to as wiring closets.
Shielded twisted pair (STP) - Usually Category 5, 5e, or 6 cable that has a foil shielding to protect from outside electromagnetic interference (EMI). In an Ethernet environment, the distance limitation is approximately 328 feet (100 meters).
Unshielded twisted pair (UTP) - Usually Category 5, 5e, or 6 cable that does not provide extra shielding from EMI, but it is inexpensive. Cable runs should avoid electrically noisy areas. In an Ethernet environment, the distance limitation is approximately 328 feet (100 meters).
Fiber-optic cable - A medium that is not susceptible to EMI, and can transmit data faster and farther than copper. Depending on the type of fiber optics, distance limitations can be several miles (kilometers). Fiber-optic can be used for backbone cabling and high-speed connections.
coaxial is also used in networking. Coaxial is not typically used in LANs, but it is widely used in cable modem provider networks. Coaxial has a solid copper core with several protective layers including polyvinyl chloride (PVC), braided wire shielding, and a plastic covering.
Two of the most common TIA/EIA cable specifications include the 568-A and 568-B standards. Both of these standards typically use the same Cat 5 or Cat 6 cable, but with a different termination color code.
Straight-through - Connects dissimilar devices, such as a switch and a computer, or a switch and a router.
Crossover - Connects similar devices, such as two switches or two computers.
Console (or Rollover) - Connects a computer to the console port of a router or switch to do initial configuration.
A serial cable is typically used to connect the router to an Internet connection.
Patch cable - Short cable from the computer to the wall plate in the user work area
Horizontal cable - Cable from the wall plate to the IDF in the distribution area
Vertical cable - Cable from the IDF to the MDF in the backbone area of the business
Backbone cable - Network part that handles the major traffic
Location of wiring closet - Area to concentrate the end-user cables to the hub or switch
Cable management system - Trays and straps used to guide and protect cable runs
Cable labeling system - Labeling system or scheme to identify cables
Electrical considerations - Outlets and other items to support the electrical requirements of the network equipment
ISP There is generally two options for obtaining new equipment:
Integrated Service Routers (ISRs) are network devices that combine the functionality of switches, routers, access points, and firewalls into the same device.
Managed service - The equipment is obtained from the ISP through a lease or some other agreement, and the ISP is responsible for updating and maintaining the equipment.
In-house - The customer purchases the equipment, and the customer is responsible for the updates, warranties, and maintenance of the equipment.
To send and receive messages on an IP network, every network host must be assigned a unique 32-bit IP address
First bit is 0, the network is a Class A, and the first octet represents the network ID.
When the first bit is 1, the router examines the second bit. If that bit is 0, the network is a Class B.
router uses the first 16 bits for the network ID. If the first three bits are 110, it indicates a Class C address. Class C addresses use the first 24 bits, or three octets, to designate the network. available network designations from 256 to over two million.
Class E-is 11110 (reserved for future use-27 Bits)
Private network addresses are not to be routed across the Internet. This allows multiple networks in various locations to use the same private addressing scheme without creating addressing conflicts
In the original IP address hierarchy, there are two levels: a network and a host. In a classful addressing scheme, the first three leading bit values are used to determine that an IP address is either a Class A, B, or C.
One thing to keep in mind is that in all IPv4 networks, two host addresses are reserved: the all-0s and the all-1s.
The original classful subnetting design required that all subnets of a single classed network be the same size. This was because routers did not include subnet mask information in their routing updates.
Variable length subnet masking (VLSM) helps to solve this issue. VLSM addressing allows an address space to be divided into networks of various sizes.
In addition to VLSM, Classless Inter-Domain Routing (CIDR) was proposed in RFC 1519 and accepted. CIDR ignores network classes based on the value of the high-order bits. CIDR identifies networks based solely on the number of bits in the network prefix, which corresponds to the number of 1s in the subnet mask.
NAT allows a large group of private users to access the Internet by sharing one or more public IP addresses. Address translation is similar to how a telephone system works in a company.
Static NAT allows hosts on the public network to access selected hosts on a private network.
If a device on the inside network needs to be accessible from the outside, use static NAT.
Static NAT is for permanent one -to -one translation from a specific inside-local ip address to a specific inside-global ip address.
PAT,can be used to add a port number to the IP address for specific connections.
The Cisco Internetwork Operating System (IOS) software provides features that enable a Cisco device to send and receive network traffic using a wired or wireless network.
The router bootup process has three stages.
1.Perform Power-on self test (POST) and load the bootstrap program.
2.Locate and load the Cisco IOS software.
3.Locate and execute the startup configuration file or enter setup mode.
two methods to connect a PC to a network device to perform configuration and monitoring tasks: out-of-band management and in-band management.
Technicians use out-of-band management to initially configure a network device, because until properly configured, the device cannot participate in the network.
A serial connection can be used to connect networks that are separated by large geographic distances. These WAN network interconnections require a telecommunications service provider (TSP).
The protocol encapsulation must be the same at both ends of a serial connection. Some encapsulation types require authentication parameters, like username and password, to be configured. Encapsulation types include:
The LAN configuration settings enable the router interface to participate on the connected local network.
Use in-band management to monitor and make configuration changes to a network device over a network connection.
The Cisco IOS command line interface (CLI) is a text-based program that enables entering and executing Cisco IOS commands to configure, monitor, and maintain Cisco devices. The Cisco CLI can be used with either in-band or out-of-band management tasks.
Security Device Manager (SDM) is a web-based GUI device management tool. Unlike CLI, SDM can be used only for in-band management tasks.
SDM Express simplifies the initial router configuration. It uses a step-by-step approach to create a basic router configuration quickly and easily.
Additional DHCP configuration parameters include:
Domain name for the organization - This name is given to the hosts as part of the DHCP configuration.
Primary domain name server - IP address of the primary DNS server. Used to resolve URLs and names on the network.
Secondary domain name server - IP address of a secondary DNS sever, if available. Used if the primary DNS server does not respond.
The Basic NAT Wizard configures Dynamic NAT with PAT, by default. PAT enables the hosts on the internal local network to share the single registered IP address assigned to the WAN interface. In this manner, hosts with internal private addresses can have access to the Internet.
Serial and Ethernet interfaces are the most common. Local network connections use Ethernet interfaces
If the NVRAM fails or becomes corrupt and the router cannot load the startup configuration file, another copy is available.
To assign an address to a switch, the address must be assigned to a virtual local area network VLAN interface.
To connect the switch to a router, use a straight-through cable. LED lights on the switch and router indicate that the connection is successful.
A router uses a routing table to determine where to send packets. The routing table contains a set of routes. Each route describes which gateway or interface the router uses to reach a specified network.
A route has four main components:
A router uses a routing table to determine where to send packets. The routing table contains a set of routes.Static routes are manually configured by a network administrator. Configuring a static route on a Cisco router requires these steps:
Step 1. Connect to the router using a console cable.
Step 2. Open a HyperTerminal window to connect with the first router that you want to configure.
Step 3. Enter privileged mode by typing enable at the R1> prompt. Note how the > symbol changes to a # to indicate that privilege mode is being used.
Routers use routing protocols to dynamically manage information received from their own interfaces and from other routers. Routing protocols can also be configured to manage manually entered routes.
The method that a routing protocol uses to determine the best route is called a routing algorithm.Routing Information Protocol (RIP) is a distance vector routing protocol that is used in thousands of networks throughout the world. It was initially specified in RFC 1058.
Characteristics of RIP include:
Defines a hop count greater than 15 as an unreachable route
Enhanced Interior Gateway Routing Protocol (EIGRP)
EIGRP is a Cisco-proprietary, enhanced distance vector routing protocol. EIGRP was developed to address some of the limitations of other
Topological database - Collection of information gathered from all the LSAs received by the router.
Shortest Path First (SPF) algorithm - Calculation performed on the database that results in the SPF tree. The SPF tree is a map of the network as seen from the point of view of the router. The information in this tree is used to build the routing table.
Open Shortest Path First (OSPF) is a non-proprietary, link-state routing protocol described in RFC 2328. The characteristics of OSPF are:
Uses the SPF algorithm to calculate the lowest cost to a destination
The router uses what is known as the administrative distance (AD). The AD represents the “trustworthiness” of the route. The lower the AD, the more the trustworthy the route. For example, a static route has an AD of 1, whereas a RIP-discovered route has an AD of 120.
The show ip route command shows the routing table, which verifies that routes received by RIP neighbors are installed in the routing table.
The debug ip rip command can be used to observe the networks advertised in the routing updates as they are sent and received.
The show ip protocols command verifies that RIP routing is configured, that the correct interfaces are sending and receiving RIP updates, and that the router is advertising the correct networks.
Autonomous Systems (AS), =Instead, the Internet is divided up into collections of networks called Autonomous Systems (AS), which are independently controlled by different organizations and companies.
Interior Gateway Protocols (IGPs) are used to exchange routing information within an AS or individual organization. The purpose of an interior routing protocol is to find the best path through the internal network.
exterior gateway protocols (EGPs) are designed to exchange routing information between different autonomous systems. Because each AS is managed by a different administration and may use different interior protocols, networks must use a protocol that can communicate between diverse systems. The EGP serves as a translator for ensuring that external routing information gets successfully interpreted inside each AS network.
border gateways EGPs run on the exterior routers. These are the routers that are located at the border of an AS. Exterior routers are also called border gateways, or boundary routers.
The most common exterior routing protocol on the Internet today is Border Gateway Protocol (BGP). It is estimated that 95% of autonomous systems use BGP.
The flow of messages in the Internet is called traffic. Internet traffic can be categorized in one of two ways:
Local traffic - Traffic carried within an AS that either originated in that same AS, or is intended to be delivered within that AS. This is like local traffic on a street.
Transit traffic - Traffic that was generated outside that AS and can travel through the internal AS network to be delivered to destinations outside the AS. This is like through traffic on a street.
ISPs offer managed services that enable these organizations to have access to the leading network technologies and applications without having to make large investments in equipment and support.
To meet customer expectations, the service offerings have to be reliable and available.
Reliability can be measured in two ways: mean time between failure (MTBF) and mean time to repair MTTR.
Equipment manufacturers specify MTBF based on tests they perform as part of manufacturing. The measure of equipment robustness is fault tolerance. The longer the MTBF, the greater the fault tolerance.
MTTR is established by warranty or service agreements.
To provide support for the multiple end-user applications that rely on TCP/IP for delivery, it is important for the ISP support personnel to be familiar with the operation of the TCP/IP protocols.
SP servers need to be able to support multiple applications for many different customers. For this support, they must use functions provided by the two TCP/IP transport protocols, TCP and UDP.
like web serving and email accounts, also depend on underlying TCP/IP protocols to ensure their reliable delivery.
Domain Name System (DNS) - Resolves Internet names to IP addresses.
HyperText Transfer Protocol (HTTP) -Transfers files that make up the web pages of the World Wide Web.
Simple Mail Transfer Protocol (SMTP) - Transfers mail messages and attachments.
Telnet - Terminal emulation protocol that provides remote access to servers and networking devices.
File Transfer Protocol (FTP) - Transfers files between systems interactively.
Bootstrap Protocol-enables diskless workstation to diuacover ite own IP address, the IP assress of a BooTP server on the network,and file to be loaded into memory to boot the machine .
BOOTP is being superseded by DHCP.
Different types of data can have unique requirements. For some applications, communication segments must arrive in a specific sequence to be processed successfully.
Additionally, the lower layers are not aware that there are multiple applications sending data on the network.
The TCP/IP model and the OSI model have similarities and differences.
Use of layers to visualize the interaction of protocols and services
Used in the networking field when referring to protocol interaction
OSI model breaks the function of the TCP/IP Application Layer into distinct layers. The upper three layers of the OSI model specify the same functionality as the Application Layer of the TCP/IP model.
The TCP/IP suite does not specify protocols for the physical network interconnection. The two lower layers of the OSI model are concerned with access to the physical network and the delivery of bits between hosts on a local network.
. UDP is considered a “best effort” Transport Layer protocol because it does not provide error checking, guaranteed data delivery, or flow control. Because UDP is a “best effort” protocol, UDP datagrams may arrive at the destination out of order, or may even be lost all together.
Before a TCP session can be used, the source and destination hosts exchange messages to set up the connection over which data segments can be sent.
This SYN, SYN-ACK, ACK activity between the TCP processes on the two hosts is called a three-way handshake
The main differences between TCP and UDP are the specific functions that each protocol implements and the amount of overhead incurred.
A socket pair, consisting of the source and destination IP addresses and port numbers, is also unique and identifies the specific conversation between the two hosts.
DNS uses a hierarchical system to provide name resolution. The hierarchy looks like an inverted tree, with the root at the top and branches below.
At the top of the hierarchy, the root servers maintain records about how to reach the top-level domain servers, which in turn have records that point to the second-level domain servers.
DNS zones can be either a forward lookup or reverse lookup zone. They can also be either a primary or a secondary forward or reverse lookup zone. Each zone type has a specific role within the overall DNS infrastructure.
A forward lookup zone is a standard DNS zone that resolves fully qualified domain names to IP addresses. This is the zone type that is most commonly found when surfing the Internet.
A reverse lookup zone is a special zone type that resolves an IP address to a fully qualified domain name. Some applications use reverse lookups to identify computer systems that are actively communicating with them.
Reverse lookups on IP addresses can be found using the ping -a [ip_address] command.
For secure communication across the Internet, Secure HTTP (HTTPS) is used for accessing or posting web server information. HTTPS can use authentication and encryption to secure data as it travels between the client and server.
HTTPS is HTTP over secure socket layer (SSL). HTTPS uses the same client request-server response process as HTTP, but the data stream is encrypted with SSL before being transported across the network.
FTP is a connection-oriented protocol that uses TCP to communicate between a client FTP process and an FTP process on a server.
DTP is a separate data transfer function. This function is enabled only when the user wants to actually transfer files to or from the FTP server.
Any active Internet connection for a computer can make that computer a target for malicious activity.
Some of the security services that an ISP support technician can provide include:
-Helping clients to create secure passwords for devices.
-Securing applications using patch management and software upgrades.
-Removing unnecessary applications and services that can create vulnerabilities.
-Ensuring applications and services are available to the users that need them and no one else.
-Configuring desktop firewalls and virus-checking software.
-Performing security scans on software and services to determine vulnerabilities that the technician must protect from attack.
When assigning permissions to files and folders, a security best practice is to apply permissions based on the “principle of least privilege”.
Authentication, Authorization, and Accounting (AAA) is a three-step process used by network administrators to make it difficult for attackers to gain access to a network.
IP Security (IPSec) is another Network Layer security protocol that can be used to secure any Application Layer protocol used for communication.
ISPs must be able to filter out network traffic, such as DoS attacks, that can be harmful to the operation of their network or servers. Port filtering and access control lists (ACL) can be used to control traffic to servers and networking equipment.
A firewall is network hardware or software that defines which traffic can come into and go out of sections of the network and how traffic is handled.
Firewalls use ACLs to control which traffic is passed or blocked. They are constantly evolving as new capabilities are developed and new threats are discovered.
A DMZ is used to store servers that users from the Internet are allowed to access. Only traffic that is permitted access to these servers is permitted into the DMZ
An IDS is a software- or hardware-based solution that passively listens to network traffic. Network traffic does not pass through an IDS device. Instead, the IDS device monitors traffic through a network interface. When the IDS detects malicious traffic, it sends an alert to a preconfigured management station.
An IPS is an active physical device or software feature. Traffic travels in one interface of the IPS and out the other. The IPS examines the actual data packets that are in the network traffic and works in real time to permit or deny packets that want access into the network
Some ISPs offer services to create wireless hot spots for customers to log on to wireless local-area networks (WLANs). A wireless network is easy to implement, but is vulnerable when not properly configured. Because the wireless signal travels through walls, it can be accessed outside the business premises. A wireless network can be secured by changing the default settings, enabling authentication, or enabling MAC address filtering.
In addition to host-based firewalls, anti-X software can be installed as a more comprehensive security measure. Anti-X software protects computer systems from viruses, worms, spyware, malware, phishing, and even spam
An SLA typically includes the following parts:
Service description, Costs, Tracking and reporting ,Problem management, Security Termination, Penalties for service outages, Availability, performance, and reliability
Traditional in-band management protocols include Telnet, SSH, HTTP, and Simple Network Management Protocol (SNMP).
Out-of-band management is useful in initial configurations if the device is not accessible via the network, or if a visual inspection of the device is necessary.
The management station contains the SNMP management applications that the administrator uses to configure devices on the network. It also stores data about those devices. The management station collects information by polling the devices. A poll occurs when the management station requests specific information from an agent.
Storing device logs and reviewing them periodically is an important part of network monitoring. Syslog is the standard for logging system events. Like SNMP, syslog is an Application Layer protocol that enables devices to send information to a syslog daemon that is installed and running on a management station.
Data backup is essential. The job of an IT professional is to reduce the risks of data loss and provide mechanisms for quick recovery of any data that is lost.
In addition to backing up server files, it is also necessary for the ISP to protect configurations and the Cisco IOS software used on networking devices owned by the ISP. The Cisco networking device software and configuration files can be saved to a network server using TFTP and variations of the copy command. The command to save the IOS file is very similar to the command to backup and save a running configuration file.
When designing a disaster recovery plan, it is important to understand the needs of the organization. It is also important to gain the support necessary for a disaster recovery plan
here are five major phases to creating and implementing a disaster recovery plan:
One of the most important abilities for a network professional to develop is the ability to efficiently troubleshoot network problems.
When troubleshooting, many technicians use the OSI and TCP/IP networking models to help isolate the cause of a problem
The upper layers (5-7) of the OSI model deal with specific application functionality and are generally implemented only in software. Problems isolated to these layers can frequently be caused by end-system software configuration errors on clients and servers.
The lower layers (1-4) of the OSI model handle data-transport issues.
The Network Layer (Layer 3) and the Transport Layer (Layer 4) are generally implemented only in software. In addition to software errors on end systems, software configuration errors on routers and firewalls account for many problems isolated to these layers. IP addressing and routing errors occur at Layer 3.
The Physical Layer (Layer 1) and Data Link Layer (Layer 2) are implemented in both hardware and software. The Physical Layer is closest to the physical network medium, such as the network cabling, and is responsible for actually placing information on the medium. Hardware problems and incompatibilities cause most Layer 1 and Layer 2 problems.
There are three main troubleshooting approaches when using network models:
Top-down, Bottom-up, Divide-and-conquer.
Network Management System (NMS) tools monitor network performance. They graphically display a physical view of the network devices. If a failure occurs, the tool can locate the source of the failure and determine whether it was caused by malware, malicious activity, or a failed device.
Network device vendor knowledge bases have become indispensable sources of information. When online knowledge bases are combined with Internet search engines, a network administrator has access to a vast pool of experience-based information.
A protocol analyzer decodes the various protocol layers in a recorded frame and presents this information in a relatively easy-to-use format. Protocol analyzers can capture network traffic for analysis.
Sometimes failures in the lower layers of the OSI model cannot be easily identified with software tools. In these instances, it may be necessary to use hardware troubleshooting tools, such as cable testers, multimeters, and network analyzers.
To troubleshoot device hardware failures and boot errors, it is first necessary to review the process that Cisco IOS devices use during startup. The bootup process has three stages:
1. Performing the POST and loading the bootstrap program.
2. Locating and loading the Cisco IOS software.
3. Locating and loading the startup configuration file or entering setup mode.
When a device fails POST, no output appears on the console screen. In addition, system LEDs may change color or blink, depending on the device type.
If the image file in flash is corrupt or missing. ROMmon commands to reload the correct Cisco IOS image from a TFTP server.
The output for the show ip interface brief command includes a summary of the device interfaces, including the IP address and interface status.
The first step in troubleshooting LAN connectivity issues is to verify that the switch port connected to the user is active and that the appropriate LED indicators are lit. If there is physical access to the switch, it can save time to look at the port LEDs, which give the link status or indicate an error condition (if red or orange). Check to see that both sides of the connection have a link.
Normally, this situation is identified by using Cisco IOS show commands to determine if the port has many packet errors, or if the port constantly flaps (loses and regains a link).
When a host running Microsoft Windows does not receive an address from a DHCP server, it automatically assigns itself an address on the 169.254.0.0 network. If this occurs, use the show ip dhcp binding command to check whether the DHCP server has available addresses .
verify that IP addressing is assigned using the Windows command, ipconfig /all. If hosts are not receiving IP addressing assignments, it is necessary to troubleshoot the DHCP configuration.
If the hosts on the internal network are assigned private addresses, NAT is required to communicate with the public network. Usually the first indication that there is a NAT problem is that users cannot reach sites located on the Internet. There are three types of address translation: static, dynamic, and PAT. Two common types of configuration errors affect all three translation methods
Verify that there is a route to the Internet for the translated addresses. Use traceroute to determine the path the translated packets are taking and verify that the route is correct.
TCP/IP utilities, such as ping and traceroute, are used to verify connectivity. Telnet can be used to verify connectivity and make configuration changes. Cisco IOS show commands display a snapshot of a configuration or the status of a particular component.
Using the “divide and conquer” method of troubleshooting, begin with verifying Layer 3 connectivity.
Step 1. Ping the host default gateway.
Step 2. Verify end-to-end connectivity.
Step 3. Verify the routing configuration.
Step 4. Ensure that NAT is working correctly.
Step 5. Check for firewall filter rules.
Source: http://tuanpham08.wordpre>ss.com
А так же :
Основные понятия брэндинга
С брэндом связано несколько понятий, которыми оперируют специалисты. Каждый брэнд обладает определенными атрибутами (Brand Attributes) - функциональными или эмоциональными ассоциациями, присвоенными брэнду покупателями и потенциальными клиентами. Атрибуты брэнда могут быть как позитивными, так и негативными, могут иметь различную силу и важность для разных сегментов рынка.
Это относится и к самому простому виду знания – чувственному восприятию.
