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Shielded twisted pair (STP or STP-A), shielded twisted pair or STP is a twisting pair cable that has protection from metal to protect the cable from external electromagnetic intereferensi. For network installation at this point is usually used category 5 UTP cabling.

How to installation of cable in order for the second color system. you can see the image below

Hopefully useful for those who want to know how the composition of network cabling (LAN)

The IP Route Command

The IP Route Command

The command for configuring a static route is ip route. The complete syntax for configuring a static route is:

Router(config)#ip route prefix mask {ip-address | interface-type interface-number [ip-address]} [distance] [name] [permanent] [tag tag]

Most of these parameters are not relevant for this chapter or for your CCNA studies. As shown in the figure, we will use a simpler version of the syntax:

Router(config)#ip route network-address subnet-mask {ip-address | exit-interface }

Purpose and Command Syntax OF IP Route

Purpose and Command Syntax of ip routePurpose and Command Syntax of ip route
Justify Full
As we have discussed previously, a router can learn about remote networks in one of two ways:
Manually, from configured static routes
Automatically, from a dynamic routing protocol

The rest of this chapter focuses on configuring static routes. Dynamic routing protocols are introduced in the next chapter.

Static routes

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Router Connections

Router Connections

Connecting a router to a network requires a router interface connector to be coupled with a cable connector. As you can see in the figure, Cisco routers support many different connector types.

Serial Connectors
Cisco elaerning Router ConnectionsPicture Router Connections

Role Of The Router

The router is a special-purpose computer that plays a key role in the operation of any data network. Routers are primarily responsible for interconnecting networks by:
Determining the best path to send packets
Forwarding packets toward their destination

Routers perform packet forwarding by learning about remote networks and maintaining routing information. The router is the junction or intersection that connects multiple IP networks. The routers primary forwarding decision is based on Layer 3 information, the destination IP address.
Role Of  The Router

Best Path Best Path And Metric

Determining a router's best path involves the evaluation of multiple paths to the same destination network and selecting the optimum or "shortest" path to reach that network. Whenever multiple paths to reach the same network exist, each path uses a different exit interface on the router to reach that network. The best path is selected by a routing protocol based on the value or metric it uses to determine the distance to reach a network. Some routing protocols, such as RIP, use simple hop-count, which the number of routers between a router and the destination network. Other routing protocols, such as OSPF, determine the shortest path by examining the bandwidth of the links, and using the links with the fastest bandwidth from a router to the destination network.

Dynamic routing protocols typically use their own rules and metrics to build and update routing tables. A metric is the quantitative value used to measure the distance to a given route. The best path to a network is the path with the lowest metric. For example, a router will prefer a path that is 5 hops away over a path that is 10 hops away.

The primary objective of the routing protocol is to determine the best paths for each route to include in the routing table. The routing algorithm generates a value, or a metric, for each path through the network. Metrics can be based on either a single characteristic or several characteristics of a path. Some routing protocols can base route selection on multiple metrics, combining them into a single metric. The smaller the value of the metric, the better the path.

Comparing Hop Count and Bandwidth Metrics

Two metrics that are used by some dynamic routing protocols are:
Hop count-Hop count is the number of routers that a packet must travel through before reaching its destination. Each router is equal to one hop. A hop count of four indicates that a packet must pass through four routers to reach its destination. If multiple paths are available to a destination, the routing protocol, such as RIP, picks the path with the least number of hops.
Bandwidth-Bandwidth is the data capacity of a link, sometimes referred to as the speed of the link. For example, Cisco's implementation of the OSPF routing protocol uses bandwidth as its metric. The best path to a network is determined by the path with an accumulation of links that have the highest bandwidth values, or the fastest links. The use of bandwidth in OSPF will be explained in Chapter 11.

Note: Speed is technically not an accurate description of bandwidth because all bits travel at the same speed over the same physical medium. Bandwidth is more accurately defined as the number of bits that can be transmitted over a link per second.

When hop count is used as the metric, the resulting path may sometimes be suboptimal. For example, consider the network shown in the figure. If RIP is the routing protocol used by the three routers, then R1 will choose the suboptimal route through R3 to reach PC2 because this path has fewer hops. Bandwidth is not considered. However, if OSPF is used as the routing protocol, then R1 will choose the route based on bandwidth. Packets will be able to reach their destination sooner using the two, faster T1 links as compared to the single, slower 56 Kbps link.

Packet Fields and Frame Fields

As we discussed previously, routers make their primary forwarding decision by examining the destination IP address of a packet. Before sending a packet out the proper exit interface, the IP packet needs to be encapsulated into a Layer 2 data link frame. Later in this section we will follow an IP packet from source to destination, examining the encapsulation and decapsulation process at each router. But first, we will review the format of a Layer 3 IP packet and a Layer 2 Eternet frame.

Internet Protocol (IP) Packet Format

The Internet Protocol specified in RFC 791 defines the IP packet format. The IP packet header has specific fields that contain information about the packet and about the sending and receiving hosts. Below is a list of the fields in the IP header and a brief description for each one. You should already be familiar with destination IP address, source IP address, version, and Time To Live (TTL ) fields. The other fields are important but are outside the scope of this course.
Version - Version number (4 bits); predominant version is IP version 4 (IPv4)
IP header length - Header length in 32-bit words (4 bits)
Precedence and type of service - How the datagram should be handled (8 bits); the first 3 bits are precedence bits (this use has been superseded by Differentiated Services Code Point [DSCP], which uses the first 6 bits [last 2 reserved])
Packet length - Total length (header + data) (16 bits)
Identification - Unique IP datagram value (16 bits)
Flags - Controls fragmenting (3 bits)
Fragment offset - Supports fragmentation of datagrams to allow differing maximum transmission units (MTUs) in the Internet (13 bits)
Time to Live (TTL) - Identifies how many routers can be traversed by the datagram before being dropped (8 bits)
Protocol - Upper-layer protocol sending the datagram (8 bits)
Header checksum - Integrity check on the header (16 bits)
Source IP address - 32-bit source IP address (32 bits)
Destination IP address - 32-bit destination IP address (32 bits)
IP options - Network testing, debugging, security, and others (0 or 32 bits, if any)

MAC Layer Frame Format

The Layer 2 data link frame usually contains header information with a data link source and destination address, trailer information, and the actual transmitted data. The data link source address is the Layer 2 address of the interface that sent the data link frame. The data link destination address is the Layer 2 address of the interface of the destination device. Both the source and destination data link interfaces are on the same network. As a packet is forwarded from router to router, the Layer 3 source and destination IP addresses will not change; however, the Layer 2 source and destination data link addresses will change. This process will be examined more closely later in this section.

Note: When NAT (Network Address Translation) is used, the destination IP address does change, but this process is of no concern to IP and is a process performed within a company's network. Routing with NAT is discussed in a later course.

The Layer 3 IP packet is encapsulated in the Layer 2 data link frame associated with that interface. In this example, we will show the Layer 2 Ethernet frame. The figure shows the two compatible versions of Ethernet. Below is a list of the fields in an Ethernet frame and a brief description of each one.
Preamble - Seven bytes of alternating 1s and 0s, used to synchronize signals
Start-of-frame (SOF) delimiter - 1 byte signaling the beginning of the frame
Destination address - 6 byte MAC address of the sending device on the local segment
Source address - 6 byte MAC address of the receiving device on the local segment
Type/length - 2 bytes specifying either the type of upper layer protocol (Ethernet II frame format) or the length of the data field (IEEE 802.3 frame format)
Data and pad - 46 to 1500 bytes of data; zeros used to pad any data packet less than 46 bytes
Frame check sequence (FCS) - 4 bytes used for a cyclical redundancy check to make sure the frame is not corrupted

Routing Table Principles

At times in this course we will refer to three principles regarding routing tables that will help you understand, configure, and troubleshoot routing issues. These principles are from Alex Zinin's book, Cisco IP Routing.

1. Every router makes its decision alone, based on the information it has in its own routing table.

2. The fact that one router has certain information in its routing table does not mean that other routers have the same information.

3. Routing information about a path from one network to another does not provide routing information about the reverse, or return, path.

What is the effect of these principles? Let's look at the example in the figure.

1. After making its routing decision, router R1 forwards the packet destined for PC3 to router R2. R1 only knows about the information in its own routing table, which indicates that router R2 is the next-hop router. R1 does not know whether or not R2 actually has a route to the destination network.

2. It is the responsibility of the network administrator to make sure that all routers within their control have complete and accurate routing information so that packets can be forwarded between any two networks. This can be done using static routes, a dynamic routing protocol, or a combination of both.

3. Router R2 was able to forward the packet toward PC3's destination network. However, the packet from PC2 to PC1 was dropped by R2. Although R2 has information in its routing table about the destination network of PC1, we do not know if it has the information for the return path back to PC1's network.

Asymmetric Routing

Because routers do not necessarily have the same information in their routing tables, packets can traverse the network in one direction, using one path, and return via another path. This is called asymmetric routing. Asymmetric routing is more common in the Internet, which uses the BGP routing protocol than it is in most internal networks.

This example implies that when designing and troubleshooting a network, the network administrator should check the following routing information:
Is there a path from source to destination available in both directions?
Is the path taken in both directions the same path? (Asymmetrical routing is not uncommon, but sometimes can pose additional issues.)
Related Topic Router

Dynamic Routing

Remote networks can also be added to the routing table by using a dynamic routing protocol. In the figure, R1 has automatically learned about the network from R2 through the dynamic routing protocol, RIP (Routing Information Protocol). RIP was one of the first IP routing protocols and will be fully discussed in later chapters.

Note: R1's routing table in the figure shows that R1 has learned about two remote networks: one route that dynamically used RIP and a static route that was configured manually. This is an example of how routing tables can contain routes learned dynamically and configured statically and is not necessarily representative of the best configuration for this network.

Dynamic routing protocols are used by routers to share information about the reachability and status of remote networks. Dynamic routing protocols perform several activities, including:
Network discovery
Updating and maintaining routing tables

Automatic Network Discovery

Network discovery is the ability of a routing protocol to share information about the networks that it knows about with other routers that are also using the same routing protocol. Instead of configuring static routes to remote networks on every router, a dynamic routing protocol allows the routers to automatically learn about these networks from other routers. These networks - and the best path to each network - are added to the router's routing table and denoted as a network learned by a specific dynamic routing protocol.

Maintaining Routing Tables

After the initial network discovery, dynamic routing protocols update and maintain the networks in their routing tables. Dynamic routing protocols not only make a best path determination to various networks, they will also determine a new best path if the initial path becomes unusable (or if the topology changes). For these reasons, dynamic routing protocols have an advantage over static routes. Routers that use dynamic routing protocols automatically share routing information with other routers and compensate for any topology changes without involving the network administrator.

IP Routing Protocols

There are several dynamic routing protocols for IP. Here are some of the more common dynamic routing protocols for routing IP packets:
RIP (Routing Information Protocol)
IGRP (Interior Gateway Routing Protocol)
EIGRP (Enhanced Interior Gateway Routing Protocol)
OSPF (Open Shortest Path First)
IS-IS (Intermediate System-to-Intermediate System)
BGP (Border Gateway Protocol)

Note: RIP (versions 1 and 2), EIGRP, and OSPF are discussed in this course. EIGRP and OSPF are also explained in more detail in CCNP, along with IS-IS and BGP. IGRP is a legacy routing protocol and has been replaced by EIGRP. Both IGRP and EIGRP are Cisco proprietary routing protocols, whereas all other routing protocols listed are standard, non-proprietary protocols.

Once again, remember that in most cases, routers contain a combination of static routes and dynamic routes in the routing tables. Dynamic routing protocols will be discussed in more detail in Chapter 3, "Dynamic Routing Protocols."
Related Topic Router

Static Routing

Remote networks are added to the routing table either by configuring static routes or enabling a dynamic routing protocol. When the IOS learns about a remote network and the interface that it will use to reach that network, it adds that route to the routing table as long as the exit interface is enabled.

A static route includes the network address and subnet mask of the remote network, along with the IP address of the next-hop router or exit interface. Static routes are denoted with the code S in the routing table as shown in the figure. Static routes are examined in detail in the next chapter.

When to Use Static Routes

Static routes should be used in the following cases:
A network consists of only a few routers. Using a dynamic routing protocol in such a case does not present any substantial benefit. On the contrary, dynamic routing may add more administrative overhead.
A network is connected to the Internet only through a single ISP. There is no need to use a dynamic routing protocol across this link because the ISP represents the only exit point to the Internet.
A large network is configured in a hub-and-spoke topology. A hub-and-spoke topology consists of a central location (the hub) and multiple branch locations (spokes), with each spoke having only one connection to the hub. Using dynamic routing would be unnecessary because each branch has only one path to a given destination-through the central location.

Typically, most routing tables contain a combination of static routes and dynamic routes. But, as stated earlier, the routing table must first contain the directly connected networks used to access these remote networks before any static or dynamic routing can be used.

Building Routing Table

Introducing the Routing Table

The primary function of a router is to forward a packet toward its destination network, which is the destination IP address of the packet. To do this, a router needs to search the routing information stored in its routing table.

A routing table is a data file in RAM that is used to store route information about directly connected and remote networks. The routing table contains network/next hop associations. These associations tell a router that a particular destination can be optimally reached by sending the packet to a specific router that represents the "next hop" on the way to the final destination. The next hop association can also be the outgoing or exit interface to the final destination.

The network/exit-interface association can also represent the destination network address of the IP packet. This association occurs on the router's directly connected networks.

A directly connected network is a network that is directly attached to one of the router interfaces. When a router interface is configured with an IP address and subnet mask, the interface becomes a host on that attached network. The network address and subnet mask of the interface, along with the interface type and number, are entered into the routing table as a directly connected network. When a router forwards a packet to a host, such as a web server, that host is on the same network as a router's directly connected network.

A remote network is a network that is not directly connected to the router. In other words, a remote network is a network that can only be reached by sending the packet to another router. Remote networks are added to the routing table using either a dynamic routing protocol or by configuring static routes. Dynamic routes are routes to remote networks that were learned automatically by the router, using a dynamic routing protocol. Static routes are routes to networks that a network administrator manually configured.

Note: The routing table-with its directly-connected networks, static routes, and dynamic routes-will be introduced in the following sections and discussed in even greater detail throughout this course.

The following analogies may help clarify the concept of connected, static, and dynamic routes:
Directly Connected Routes - To visit a neighbor, you only have to go down the street on which you already live. This path is similar to a directly-connected route because the "destination" is available directly through your "connected interface," the street.
Static Routes - A train uses the same railroad tracks every time for a specified route. This path is similar to a static route because the path to the destination is always the same.
Dynamic Routes - When driving a car, you can "dynamically" choose a different path based on traffic, weather, or other conditions. This path is similar to a dynamic route because you can choose a new path at many different points on your way to the destination.

The show ip route command

As shown in the figure the routing table is displayed with the show ip route command. At this point, there have not been any static routes configured nor any dynamic routing protocol enabled. Therefore, the routing table for R1 only shows the router's directly connected networks. For each network listed in the routing table, the following information is included:
C - The information in this column denotes the source of the route information, directly connected network, static route or a dynamic routing protocol. The C represents a directly connected route. - This is the network address and subnet mask of the directly connected or remote network. In this example, both entries in the routing table, 192.168.1./24 and, are directly connected networks.
FastEthernet 0/0 - The information at the end of the route entry represents the exit interface and/or the IP address of the next-hop router. In this example, both FastEthernet 0/0 and Serial0/0/0 are the exit interfaces used to reach these networks.

When the routing table includes a route entry for a remote network, additional information is included, such as the routing metric and the administrative distance. Routing metrics, administrative distance, and the show ip route command are explained in more detail in later chapters.

PCs also have a routing table. In the figure, you can see the route print command output. The command reveals the configured or acquired default gateway, connected, loopback, multicast, and broadcast networks. The output from route print command will not be analyzed during this course. It is shown here to emphasize the point that all IP configured devices should have a routing table.
Adding a Connected Network to the Routing Table

As stated in the previous section, when a router's interface is configured with an IP address and subnet mask, that interface becomes a host on that network. For example, when the FastEthernet 0/0 interface on R1in the figure is configured with the IP address and the subnet mask, the FastEthernet 0/0 interface becomes a member of the network. Hosts that are attached to the same LAN, like PC1, are also configured with an IP address that belongs to the network.

When a PC is configured with a host IP address and subnet mask, the PC uses the subnet mask to determine what network it now belongs to. This is done by the operating system ANDing the host IP address and subnet mask. A router uses the same logic when an interface is configured.

A PC is normally configured with a single host IP address because it only has a single network interface, usually an Ethernet NIC. Routers have multiple interfaces; therefore, each interface must be a member of a different network. In the figure, R1 is a member of two different networks: and Router R2 is also a member of two networks: and

After the router's interface is configured and the interface is activated with the no shutdown command, the interface must receive a carrier signal from another device (router, switch, hub, etc.) before the interface state is considered "up." Once the interface is "up," the network of that interface is added to the routing table as a directly connected network.

Before any static or dynamic routing is configured on a router, the router only knows about its own directly connected networks. These are the only networks that are displayed in the routing table until static or dynamic routing is configured. Directly connected networks are of prime importance for routing decisions. Static and dynamic routes cannot exist in the routing table without a router's own directly connected networks. The router cannot send packets out an interface if that interface is not enabled with an IP address and subnet mask, just as a PC cannot send IP packets out its Ethernet interface if that interface is not configured with an IP address and subnet mask.

Note: The process of configuring router interfaces and adding network address to the routing table are discussed in the following chapter.
Related Topic Router



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