Router File System

Benefits of VLANs

VLANs make it simple to plan a network to maintain the goals of an organization. The most important benefits of  VLANs are as follows:

Security

Security in one of the primary benefits of VLANs. it makes possible that the hosts that have sensitive data are separated from the rest of the network. The separation decreases the possibility of confidential information breaches. The figure below illustrates that management, sells and IT section are totally separate from each other, so they can’t access each other’s files. 

Cost

VLANs reduce the cost of the network and make possible of more efficient use of existing hardware and bandwidth because segmenting a network into smaller VLAN is cheaper than creating a routed network with routers.

Better Network Performance 

Dividing flat Layer 2 networks into multiple broadcast domains reduces unnecessary traffic on the network and help increase network performance. VLANs manage traffic very efficiently so that your end users experience better performance. The administrator will have a smaller amount of latency problems on the network and more reliability for important applications.

Shrink Broadcast Domains 

Division of large network into smaller VLANs reduce devices in the broadcast domain. As shown in the figure above, total nine hosts working in this network but only three hosts are in broadcast domains.

Improved IT staff efficiency 

VLANs make network management very easy for IT staff because users with related network requirements share the same VLAN.

Simpler Project and Application Management 

VLANs combined users and network devices to support both business and geographic requirements.

Simplified Administration for the Network Manager

VLAN simplifies network management. Grouping of users into the virtual networks, make it easy to set up and control network policies at a group level.

Easy Troubleshooting

Network troubleshooting can be simpler and faster because of different user groups are segmented and isolated from one another. If the network administrator knows that complaints are only coming from a different subset of users, the network administrator will be able to quickly narrow down where to look to find the issue.

Virtual Local Area Network (VLANs)

One of the technologies that improve network performance is the separation of large broadcast domains into smaller ones. By design, routers block broadcast traffic. But, routers usually have a limited number of LAN interfaces. A router’s main role is to move data between different networks. The router does not provide network access to end devices. The access layer switches are responsible for connectivity to end devices. The VLAN on Layer 2 switches reduce the size of broadcast domains. VLANs are incorporated into network design making it easier for a network to support the goals of an organization. Mostly VLAN is used within switched LANs.

The VLAN create a logical broadcast domain that consists of different physical LAN segments. it improves network performance by separating large broadcast domains into smaller broadcast domains. If a device in one VLAN sends a broadcast data, all devices in that VLAN receive the data, but devices in other VLANs do not.

What is VLANs

Virtual Local Area Network provides segmentation within a switched network. It is a technique that group devices within a LAN. A group of devices within a VLAN communicate like they are connected to the same wire. VLANs are based on logical connections, in place of physical connections. it permits a network administrator to divide larger networks based on factors like function, project team, or application, without hold for the physical location of the user or device.

Devices inside a VLAN work like they are in their own independent network; though they share a common infrastructure with other VLANs. Any switch port can belong to any VLAN, and unicast; broadcast and multicast packets are forwarded and flooded only to end station within the VLANs. Every VLAN is work like a separate logical network; and data destined for stations, not in the VLAN must be forwarded through a router or device that supports routing. VLANs make possible the implementation of access and security policies to particular groupings of users. Each switch port can be assigned to only one VLAN except some cases. The figure below illustrates the layout of VLANs.

 

Cisco Borderless Networks

Collision Domains and Broadcast Domains

Collision Domains

In hub-based Ethernet segments, network devices contribute to getting the medium, because devices must take turns when transmitting. The segment of the network that shares the same bandwidth between devices is known as collision domains, in other words, a collision domain is the element of a network where collisions of packets can occur. A collision can occur when two or more devices send a packet at the same time on the shared segment.  When the packets collide, both devices must send the packets again, which reduces network efficiency. Usually, collisions occur in a hub environment, as each port on a hub is in the same collision domain. But each port on a bridge, switch and a router is in separate collision domains.

However, the switch can divide a network into segments and which reduce the number of devices that contribute to bandwidth.  Each port of the switch represents a new segment and each new segment is a new collision domain. Which provide more bandwidth to the devices on the segment, and one collision domain does not interfere with other collision domain. The figure below illustrates the collision and broadcast domain.

Broadcast Domains

A broadcast domain is a domain where the sending device sends a single copy of data and that copy of data will be delivered to every device in the network segment. A broadcast domain consists of devices that can reach each other at the data link layer by using broadcast. Each port on a hub and switch are by default in the same broadcast domain. broadcast domains. Although, switches filter frames based on MAC addresses, they do not filter broadcast frames. Switch forward must flood broadcast to all ports for other switches. If a collection of two or more switches forms as a single broadcast domain.

Network layer devices, such as a router, can feature to divide a Layer 2 broadcast domain, so each port of the router are used to segment both collision and broadcast domains. When the device sends layer 2 broadcast, the destination MAC address in the frame should be all F,s. A frame containing all F in the destination field is received by all devices in the broadcast domain.

When a switch in the network segment receives a broadcast frame, it floods the frame out to each of its ports, except the ingress port. All devices connected to the switch receive a copy of the broadcast frame and processes it. Broadcasts are an important part of the network, therefore we can’t avoid it. Broadcasts are used to initially locate other devices and network services. Many protocols like ARP and DHCP are dependent on Broadcast to function.

The broadcasts reduce the network efficiency because network bandwidth is used to propagate the broadcast traffic. A lot of broadcasts and a heavy traffic load on a network can cause in congestion: a slow-down in the network performance. When two or more switches are connected together, the broadcast domain is increased. The figure below illustrates the broadcast domains.

Data Frames Forwarding and Switching Method

With network growing, its facing slower network performance, Ethernet bridges were added to networks to limit the size of the collision domains. The advancement in integrated circuits permitted for LAN switches to replace the early bridges. The modern switches were able to move the layer 2 forwarding decision from software to application-specific-integrated-circuits (ASICs). The ASICs decrease the packet-handling time within the device and permit the device to handle an increased number of ports without degrading performance.  There are two methods of data switching and forwarding:-

• Store-and-forward method


• Cut-through Method

Store-and-Forward Switching

The store-and-forward method makes a forwarding decision when the complete frame received and then checked the frame for errors using a mathematical error-checking mechanism known as a cyclic redundancy check (CRC). if the CRC is valid, the switch looks up the destination address, which determines the outgoing interface. The frame is then forwarded out the correct port.

The Store-and-forward method has two primary characteristics that differentiate it from cut-through:

• Error checking


• Automatic buffering.

Error Checking

A switch using store-and-forward switching technique performs an error check on each incoming frame. When received the entire frame on the ingress port, as shown in the figure, the switch compares the frame-check-sequence (FCS) value in the last field of the datagram against its own FCS calculations. The FCS is the process that helps to make sure that the frame is free of physical and data-link layer errors. If the frame has no error, the switch forwards the frame to the destination; otherwise, the frame is dropped.

 

Automatic Buffering

With any difference in data speeds between the ingress and egress ports, the switch stores the whole frame in a buffer computes the FCS check; forwards it to the egress port buffer and then sends it. For example, when an incoming frame traveling into a Fast Ethernet port that must be sent out a Giga Ethernet interface would require using the store-and-forward method. The store-and-forward switching is the primary method for Cisco switches.

Cut-Through Switching

The Cut-Through Switching is another method of switching, as shown in Figure 2; this method starts the forwarding process when the destination MAC address of an incoming frame and the egress port has been determined. The advantage to this method is the ability to switch data earlier than store-and-forward method. The primary characteristics of cut-through switching are the following:

• Rapid Frame Switching


• Fragment Free

 

Rapid Frame Forwarding

A switch using the cut-through method make forwarding immediately when it has found the destination MAC address of the frame in its MAC address table. The switch doesn’t need to wait for the complete frame to receive like store-and-forward method.

A switch using the cut-through method can quickly decide because of ASICs and MAC controller. The cut-through method needs to check a larger portion of a frame’s headers for additional filtering purposes. For example, the switch can examine source MAC address; destination MAC, and the Ether Type fields which are total 14 bytes and also examine an additional 40 bytes in order to carry out more difficult functions Layers 3 and 4.

This method does not drop invalid frames. The frames with errors are forwarded next segments of the network. If there are too much invalid frames in the network, which produce a negative impact on bandwidth.

Fragment Free Switching

It is a modified form of a cut-through switching. In this form of switching the switch waits for the collision window (64 bytes) to pass before forwarding the frame. Each frame will be checked into the data field to make sure there is no fragmentation has occurred. This is provides enhanced error checking than cut-through; without any further latency and delay. The lower latency speed of cut-through switching makes it more suitable for high-performance computing (HPC) applications that need process-to-process latencies of 10 microseconds or less.

Switching Concept in Networking and Telecommunications

The switch frame forwarding is common in networking and telecommunication. Different types of switches are used in networking(LAN, WAN, and PSTN). The basic concept of switching decision is based on the following two criteria.

• Ingress port


• Destination address

The traffic forwarding decision is completed in relation to the traffic flow. The term ingress is used to explain where a frame enters to the device on a particular port. The term egress is used to describe the frames leaving the device from the particular port. When a switch makes a frame forwarding decision, it is based on the ingress port and the address of the destination host.  The networking switch maintains a MAC address table. The table is used to decide how to forward traffic through the switch. The figure below illustrates the switch MAC address table.

• If a data enters to switch port 1 and the message has a destination address of DB-CD-AC-3D-26-25, then the switch forwards the data out to port 7.


• If a data enters to switch port 6 and the message has a destination address of C3-A3-A2-35-A6-66, then the switch forwards the data out port 8.


• If a data enters switch port 2 and has a destination address of EE-01-A1-AF-00-01, then the switch forwards the data out port 1.

The network switch has only one intelligence, the ability to maintain MAC address and table make a decision to forward traffic based on the ingress port and the destination address of the message. Every switch has only one master table that describes an association between address and port. The Cisco switches forward Ethernet frames based on the destination MAC address of the frames.

The concept of Dynamically Populating a MAC Address Table

Network Switches use MAC address table to forward network traffic towards destination through the proper port. It is necessary for a switch to know which port to use to transmit data. The switch must first learn which devices exist on each port. When the switch learns the devices connected to each port, its prepare MAC address. The table also called content addressable memory (CAM) table. The CAM is a memory which is used in high-speed searching applications. The switches decide how to handle incoming data frames by maintaining the table of MAC addresses. The switch builds MAC address table by reading the MAC address of each device connected to the port of a switch and then uses MAC address table to send frames destined for a particular out the specific port which has been assigned to that device. The switch populates the table of the MAC address based on the source MAC addresses.

When a switch receives an incoming frame with a destination MAC address, if the destination MAC address not available in the table, the switch forwards the frame out of all ports except for the ingress port of the frame, this technique called flooding of data.  When destination device responds, the switch adds the source MAC address of the frame and the port where the just received to the MAC address table. Network, where multiple switches are interconnected, The MAC address table contains multiple addresses for a single port. The switch kept MAC address for a specific time, the aging time is five minutes for a single host entry. The steps below describe the process of the building MAC address table.   

The following steps describe the process of building the MAC address table:

• The switch receives a frame from Host 1 on Port 1, the MAC address table is empty (Figure 1).

• The switch examines the MAC address of the source (Host 1) and compares it to the MAC address table.


• If the address is not found in the MAC address table, it associates the MAC address of host 1 with port 1 (ingress port) in the MAC address table. (Figure 2)

• If the MAC address already exists in the table, it resets the aging timer for an entry.


• when the switch has recorded the source address information in the MAC table then switch examines the destination MAC address.


• If the destination address is not already recorded in the MAC table or if it’s a broadcast MAC address containing all Fs, the switch floods the data frame to all ports, except the ingress port (Figure 3).

• The destination Host (Host 4) will reply to the frame with a unicast frame addressed to Host 1 (Figure 4). The switch enters the source MAC address of Host 4 and the port number of the ingress port into the address table. The destination address (Host 1) of the frame and its associated egress ports found in the MAC address table.

• The switch now complete entries for host 1 and host 4 and they can now forward frames between these source and destination devices without flooding. 

Role of Switched Networks

A few years ago the flat Layer 2 switched networks were the standard. Flat Layer 2 data networks work on the basic principles of Ethernet and the common use of hub and repeaters to broadcast LAN traffic throughout a campus. As shown in Figure 1, networks have primarily changed to switched LANs in a hierarchical network. A switched LAN allows traffic management, additional flexibility, and extra features, such as:

• QoS


• Wireless network connectivity and support


• IP telephony and mobility services


• Additional security

Form Factors

Different types of switches are used in a business network. Considering common business requirement the appropriate switched equipment selection is a very important factor.  Selecting the type of switch the network administrator and designer must select a modular or fixed configuration and stackable or non-stackable. The physical installation is also an important consideration of the switch. The thickness of the switch decides where to install the switch. The switch can be installed in a rack or in a cabinet. These options are sometimes referred to as switch form factors, which I am going to explain below:-

Fixed Configuration Switches

Fixed Configuration switches are switches with a fixed number of ports and are normally not expandable. These switches do not support features or options further than those that originally came with the switch. The switch model determines the features and options available. Such as, if you have a 16-port gigabit fixed switch, you cannot add additional ports when you need them. This category is discussed in further detail below. Cisco Catalyst 2K, 3K, and the Cisco 300/500 series are good examples of Fixed Configuration switches. The Fixed configuration switch category is further broken down into:

• Unmanaged Switches


• Smart Switches


• Managed L2 and L3 Switches

Modular Configuration Switches

Modular switches are expendable switches comes with different sized chassis which allow a different number of modular line cards inside the chassis. The modular switches offer more flexibility in their configuration. If you have a 24 port modular switch you can easily expand the switch to 48 port.  

Stackable Configuration Switches

A stackable switch is a switch that is completely functional operating standalone but which can also be set up to operate jointly with one or more other switches in a group. This group of switches will show the characteristics of a single switch but have the port capacity of the sum of all switches. Stackable switches can be interconnected using a special cable that provides high-bandwidth throughput between the switches. The Cisco Stack Wise Technology allows the interconnection of nine switches in the group. These stacked switches effectively operate as a single larger switch.

Cisco Borderless Network

With the rising demands of the converged network, the recent developments in network design are the Cisco Borderless Network. The Cisco Borderless Network is a network design that allows organizations to support a borderless network that can connect any person, everywhere on any device very securely and consistently. This design address IT and business challenges.

The Cisco Borderless Network structure merge wired and wireless access, as well as access control, policy; and performance management of different device types. Using the Cisco Borderless Network architecture is built on a hierarchical infrastructure of hardware that is scalable and flexible, the Figure below illustrates the Cisco Borderless Network which provides two primary sets of services: network services and endpoint services; all services managed by an integrated management solution. This design enables different network elements to work mutually and also allow to access resources from any place at any time; as providing optimization, scalability as well as security.

Hierarchy in the Cisco Borderless Network

Availability, flexibility, security, and manageability is the primary requirement of the borderless switched network. The borderless switched network should deliver current and future requirement. The basic principles of the Borderless switched network are the following:

• hierarchical network Design


• Modularity


• Resiliency


• Flexibility

Understanding the principle to fits in the different situation is very important. The hierarchical borderless 

switched network is providing a base for the network designer to cover security, mobility, and unified communication features. Cisco designs three-tier and two-tier hierarchical network for a campus. The figure below illustrates the Cisco hierarchical network design. The three-tier of this design are the access, distribution, and core layers.  Every layer of this design can be seen as a clear structured module with particular roles and functions in the campus network.

The campus hierarchical network design which containing modularity provide critical network services with resilient and flexible.  The modularity also provide assistance for increase and change that occurs over time

Access, Distribution, and Core Layers

Access Layer

The access layer is the place where traffic enters or exits the campus network. It is the edge of the campus network. Usually, the main function of an access layer is to provide network connectivity and access to end users.  The switches of the access layer connect to switches of the distribution layer. The switches in the distribution layer apply network foundation technologies such as routing, QoS, and security.

To meet user requirement and network application, the next-generation switching platforms currently present extra converged integrated; and quick services to different types of endpoints at the edge of the network. Creating intelligence into the switches of an access layer allows applications to function on the network more capable and securely.

 Distribution Layer

The distribution layer provides connectivity between access layer and core layer with many important functions. This layer provides intelligent switching and routing. The distribution layer provides network access policy functions to access the whole network as long as differentiated services to different classes of service applications at the edge of the network. This layer providing high ease of use throughout redundant distribution layer switches to the end-user and equal cost paths to the core layer. The distribution layer also aggregate large-scale wiring closet networks and aggregate Layer 2 broadcast domains and Layer 3 routing boundaries

Core Layer

This layer is the backbone of the Cisco borderless network. The core layer connects a number of layers of the campus network and work as the aggregator for all of the other campus blocks and interconnects the campus with each other inside the network. The core layer main function is to provide speedy fault isolation and high-speed backbone connectivity.

Collapsed Core Network

Three-tier campus network usually planed for organizations where the access, distribution, and core, each are required as separate layers. This is required because of a basic, cost-effective, scalable, and efficient physical layout design for the large-scale network where many campuses exist. The best practice is to make an extended-star 

physical topology from the main campus to all other campuses.

The campus where fewer users accessing the network or single building campus usually not required a separate core and distribution layers. Network structure required in this situation is called a collapsed network or two-tier campus network.  In a collapsed network the role of the core switches moves to the distribution switches, merging the core- and distribution layer.

The figure below illustrates the collapsed campus network example for where the distribution and core layers are collapsed into a single layer.

Converged Network

The converged network is such a network that designed to handle voice, video, and data.  The network consists of Layer 3 devices and Layer 2 devices, such as routers and switches. The router should be in position of routing table to accurately and efficiently send data to remote destinations. The converged network must be developed with an architectural approach that embeds intelligence, simplifies operations, and is scalable for future demand.

Elements of a Converged Network

To support a business community networks converged solutions using voice systems, IP phones, voice gateways, video support, and video conferencing. Including data services, a converged network with teamwork support might include following features.

• Call Management - Call processing, caller Identification, call conference ,hold and transfer
• Voice Messaging
• Mobile Call Facility where required
• Automated attendant

All in one is the primary benefits of transitioning to the this type of network because there is just one physical network to install and manage all the above services. Separate network for all the above services is too costly. So, there are considerable savings over the installation and management of converged network for the above services. The converged network solution integrates IT management thus that any change and additions are completed with an keen management interface. This solution also provides computer soft phone application support and point-to-point video, thus that users can enjoy communications with the same ease of administration and use as a voice call.

The services convergence onto the network has resulted in an development in networks from a traditional data transport role to high speed data, voice, and video communication. This one physical converged network should be accurately planned and implement to allow the consistent handling of the various types of information that it must carry. A prearranged design is necessary to allow management of this difficult environment. The figure below illustrates the converged network, that one network and many types of data.

Common Show Commands - Cisco IOs

The Show commands display important information about the configuration and operation of the device in the Cisco IOs command Line Interface (CLI) mode. Network administrators use different show commands to examine device status; interfaces, process and configuration files to validate the device operational status. The status of almost all process and function of the router can be view and verify using show command. The important show commands of Cisco IOS are the following:-

• show version
• show running-config
• show arp
• show interfaces
• show protocols
• show ip protocols
• show ip route
• show ip interface brief
• show cdp neighbors

show version

The show version command on Cisco router displays hardware information. The command output gives insight into the routers capabilities. This command can be abbreviated sh ver. The output of show version command consist of following unique information:-

• IOS version
• Image filename
• System uptime
• Type of processor
• Amount of RAM
• Number of ports on the switch
• Amount of flash memory
• Current configuration register

The figure below illustrates the output of the show version command on the Cisco router.

Show running-config

This command is used to display the configuration information currently running on the terminal. We can also use this command in combination with the show startup-config command to compare the information in running memory to the information stored in NVRAM or in a place specified by the CONFIG_FILE. This command can be abbreviated sh ru

show arp

This command displays the ARP table of the router. The ARP table is the table which contains the resolved IPv4 address to MAC address mappings. If a host is can't ping? Make sure using the show arp command that you're getting an arp entry of the host that you want to ping. The command can be abbreviated sh ar .

show interfaces

The show interface command displays all type of interfaces with configuration and statistics. It is very important for the network administrator to know what interfaces are installed and configure in the router. This command provides a lot of information in the output. This command can be abbreviated as sh int.  The figure below illustrates the output of the show interface command.

show protocols

This command displays the status of configured layer three protocols on all interfaces of the Cisco routers. This command can be abbreviated as sh prot

show ip route

The show ip route command is used to show the routing table of the router. The routing table is the list of all networks that the router can communicate; their metrics and how to communicate with them. This command can be abbreviated with sh ip ro. The command also has parameters after route (ro) like sh ip ro rip for all RIP routes. The figure below illustrates the output of the show ip route command

show ip interface brief

The show ip interface brief is one of the most frequently used commands in the Cisco devices. This command provides abbreviated output than the show ip interface command. It provides an outline of the key information for all the network interfaces on a router. The figure below illustrates the output of this command.  The output displays all interfaces on the router; the IP address assigned interfaces, if any, and the operational status of the interface. The show ip interface brief command can also be used to verify the status of the switch interfaces.

Show CDP neighbors

This command display information about the Cisco devices that are connected to your current device. Cisco Discovery Protocol (CDP) is a Cisco proprietary protocol and will only detect Cisco products. To show detailed information about neighboring devices discovered using CDP; use the show cdp neighbors command in privileged EXEC mode. The command can be abbreviated with sh cd ne.

Interpreting Trace Messages

The Trace is a diagnostic utility which displays the route from host to a destination using ICMP echo packets to the destination. it proceeds a list of hops as a packet is routed through a network. it uses varying TTL values as each router down the path is required to decrement the packet's TTL by at least 1 before forwarding the packet, the TTL is working just like a hop counter. When the TTL value reaches zero (0), the router sends an ICMP "Time Exceeded" message back to the source.
The trace command sends the 1^st  echo packet with a TTL of 1 and then increment the TTL by 1 on each successive transmission, until the destination address responds or until the maximum TTL is reached.

When performing the operation from a Windows computer, the command should be tracert, for example

C:\>tracert fschub.com

C:\>tracert < target IP address >

When performing the trace from a router, the command should be traceroute, for example

Router# traceroute fschub.com

Router# traceroute < target IP address >

Figure 1 shows example output of the tracert command entered on host 4 to trace the route to host 1. The only successful response was from the gateway on Router Peshawar and from router Karak. Trace requests to the next hop (Host 1) timed out, meaning that the next hop (Host 1) did not respond. The results indicate that there is either a failure in the internetwork beyond the LAN or that this host configured not to respond to echo requests used in the trace.

Figure 2 shows an example output of the tracert command on host 4 to host 2 and the trace is completed successfully.

Following is an important switch that uses trace command.

-d -  This switch with tracert command specifies to not determine addresses to hostnames

-h maximum_hops  -Specifies the maximum number of hops to search for the target

-j host-list - Specifies loose source route along the host-list (IPv4 only)

-w timeout -Waits the number of milliseconds specified by timeout for each reply

Network Baseline

Do you know your standard network throughput volume and most types of traffic used in your network? If you have no information about the above questions then you should required baseline your network. The network baseline is one of the most useful tools for monitoring and troubleshooting network performance. For the effective network, performance baseline is required over a period of time. Measuring performance at varying times and loads will help in creating a better image of overall network performance

How to baseline a network

To baseline a network, you need to monitor the network traffic for a long time, because a wider time presents a more realistic picture of a traffic pattern. The use of a network baseline is listed below:

• Evaluate network management policies agreement.
• Understand network pattern and traffic trends.
• Speed up troubleshooting network problems.
• Understand network resources allocation.
• Provide network up-gradation history statistics.
• Provide data for decision making to network and security management.

To baseline a network, network administrators need software Colasoft nChronos and Capsa to baseline their networks. Both software is used to listen to packet data of a wire and generate all kinds of a report on the network.

Another method for starting a baseline is to copy, paste and save the results from an executed ping, trace and other related commands into a text file with time and date. These text files can be used to compare with other results, error messages and the response times from host to host. If there is a huge increase in response times, there may be a latency issue to address. The figures below illustrates the result of the ping command for the same IP address with different timings and the comparison of both. 

The output resulting from network commands can contribute data to the network baseline. Commercial networks should have widespread baselines. Professional-grade software tools are available for storing and maintaining baseline information.

Interpreting Ping Results - Cisco Devices

The ping is a very helpful utility to test and troubleshoot network devices connectivity. It uses the Internet Control Message Protocol (ICMP). The ping command indicates the source of the problem. It is an initial step in troubleshooting a network failure.

Cisco IOS Ping Indicators

There are several indicators in IOS for ICMP echo request that was sent. The common indicators for ICMP echo are the following:

! - The mark of exclamation indicates that the ping completed successfully and verifies Layer 3 connectivity along the network path. As shown in Figure below, Karak Router Successfully ping Peshawar router, which IP address is 172.16.0.1

"." The period indicates that there is some problem in connectivity somewhere along the network path. It also indicates that a router along the network path does not configure a route to the destination. If the ping is not allowed in the device it should also give a reply with “.” Indicator. The first echo request timed out is common in the network If the arp process is required. The figure below shows the ping result from Karak router to laptop 3, where “Karak router” has no route to the network 192.168.1.0/24, so its reply with request timed out “.” Indicators.

U – This indicator shows that a router along the network path responded with an ICMP unreachable message because the router did not have a route configure to the destination address. If the ping request is blocked by destination it will also reply with this mark.

Testing the Loopback

To verify the internal IP configuration and protocol stack from the network layer to the physical layer can also be used the ping command instead of putting a signal on the media. The Loopback IP addresses are 127.0.0.1 for IPv4 and ::1 for IPv6.

Extended Ping

The extended ping is one of the best commands offers by Cisco IOS. This is the extended mode of the ping command. To execute extended ping enter ping without destination address in privileged EXEC mode. As shown in the figure below, a series of different prompts are then presented asking different parameters. Pressing Enter without writing something accepts the indicated default values.

The figure below illustrates how to force the source address for a ping to be 192.168.1.1(Router Peshawar); the source address far a standard ping would be 172.16.0.2. The network administrator can verify from Peshawar Router that the Karak Router has a route to 192.168.1.0/24 network.

Router File System

The Cisco IOS File System (IFS) have different directories. The directories available depend on the device. The IFS also allow creating subdirectories in flash memory or on a disk. The figure below display the output of the show file system command, the command lists all of the available file systems on the router.

The command gives helpful information such as the information about available and free memory, the file types, and its permissions. Permissions contain read-only (wr), write-only (ro), and read and write (rw).

The asterisk against flash file system means that the current default file system is flash. The pound symbol (#) appended to the flash indicate that bootable IOS is located in flash.

The Flash File System

The figure below displays the output of the dir command. Flash is the default file system, so the dir command lists the contents of flash.

 

The NVRAM File System

To view and list the contents of NVRAM, the command will be given as dir nvram: in user exec mode. as shown in the Figure below.

Switch File Systems

The show file systems command also show the file systems on a Catalyst switch is the same as on a Cisco router, as shown in the figure.

Backup and Restoring using Text files

Backup

Using Tera Term we can also backup Configuration file and restore configuration when needed from the text file. The steps for backup and restoring using Tera Term is the following:-

1. On the File menu of Tera Term, click Log.


2. Then select location where you want to save the file. Now Tera Term will start capturing.


3. Once capture has been started, execute the show running-config or show startup-config command at the privileged EXEC prompt. The displayed text in the Tera Terminal will be directed to the chosen file.


4. After completing capture, select Close in the Tera Term: Log window.


5. View the file at the chosen location to verify that it was not corrupted.

Restoring

When configuration copied from a text file and pasted it into a terminal window, the InterOperating System executes each line of the text file as a command.  So, the captured file will require editing to make sure that encrypted passwords are in plain text and that there is no non-command text.

Furthermore, the device must be set at the global configuration mode to receive the commands from the text file being pasted into the terminal window. Following are the steps to restore configuration using Tera Term.

1. On the File menu of Tera Term, click Send File


2. Locate the configuration text file to be copied into the device and click Open.


3. Tera Term will paste the file into the device and the text will be applied as a command in the device.

Backup and Restoring Configurations with TFTP

Backup

Startup configuration or running configuration files can be stored on a TFTP (Trivial File Transfer Protocol) server and can be restored in the event of the problem. The configuration file should also be included in the network documentation. To save the running configuration or the startup configuration file to a TFTP (Trivial File Transfer Protocol) server, use the copy running-config tftp or copy startup-config tftp command. Following are the steps to back up the running configuration to a TFTP server:

1. Enter the copy running-config tftp command in user exec mode and then enter the hostname or IP  address where the configuration file will be stored.


2. Enter the name to assign to the configuration file.


3. Press Enter to confirm every choice.

The figure below illustrates the backup process to TFTP.

Restoring

To restore the running configuration or the startup configuration from a TFTP (Trivial File Transfer Protocol) server, use copy tftp running-config or copy tftp startup-config command. Following are the steps to restore the running configuration from a TFTP server:

1. Enter the copy tftp running-config command in user exec mode and then enter the host name or IP address where the configuration file is stored.


2. Enter the name to assign to the configuration file.


3. Press Enter to confirms each choice.

The Figure below illustrates the restore process from the TFTP server.

 

Backing Up and Restoring Using a USB

Backup

Before backing up to a USB port, it is important to verify that the USB drive is there and confirm the name of the drive using the show file systems command in the user exec mode. If USB drive is there, use the copy run usbflash0:/ command to copy the configuration file to the USB flash drive. Be sure to use the name of the flash drive exactly, as indicated in the file system. The slash indicates the root directory of the USB flash drive. Then the IOS will prompt for the filename. If the file already copied and exists on the USB flash drive, the router will then prompt to overwrite. We can see files and directories in the USB using dir command.

Restore

To copy the file back, use the command copy usbflash0:/Router-Config running-config to restore a running configuration where Router-Config is the backup file name in the USB.