Presentation 3 for Students of professordkinney.com

Establishing Internet Connectivity
8/2/2013
Instructional Design-Computer Networking -
Bridges Educational Group

Lessons Objectives:
 Understanding the TCP/IP Internet
 Understanding the TCP/IP Transport
 Addressing and Subnets
 Exploring the Functions of Routing
 Configuring a Cisco Router
8/2/2013

 TCP/IP (Transmission Control Protocol/Internet Protocol) is the basic
communication language or protocol of the Internet. It can also be used as a
communications protocol in a private network (either an intranet or
an extranet). When you are set up with direct access to the Internet, your
computer is provided with a copy of the TCP/IP program just as every other
computer that you may send messages to or get information from also has a
copy of TCP/IP.
 TCP/IP uses the client/server model of communication in which a computer
user (a client) requests and is provided a service (such as sending a Web page)
by another computer (a server) in the network. TCP/IP communication is
primarily point-to-point, meaning each communication is from one point
(or host computer) in the network to another point or host computer.
 Many Internet users are familiar with the even higher layer application
protocols that use TCP/IP to get to the Internet. These include the World Wide
Web's Hypertext Transfer Protocol (HTTP), the File Transfer Protocol (FTP),
Telnet (Telnet) which lets you logon to remote computers, and the Simple Mail
Transfer Protocol (SMTP). These and other protocols are often packaged
together with TCP/IP as a "suite."
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The TCP/IP Protocol Architecture
 Figure 2 shows the TCP/IP protocol architecture; this diagram is by no means
exhaustive, but shows the major protocol and application components
common to most commercial TCP/IP software packages and their
relationship.
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The Network Interface Layer
PPP
It is worth spending a little bit of time discussing PPP because of its importance in
Internet access today. As its name implies, PPP was designed to be used over
point-to-point links. In fact, it is the prevalent IP encapsulation scheme for
dedicated Internet access as well as dial-up access. One of the significant
strengths of PPP is its ability to negotiate a number of things upon initial
connection, including passwords, IP addresses, compression schemes, and
encryption schemes.
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PPP Frame Format

 PPP generally uses an HDLC-like (bit-oriented protocol) frame format as
shown in Figure 3, although RFC 1661 does not demand use of HDLC. HDLC
defines the first and last two fields in the frame:
 Flag: The 8-bit pattern "01111110" used to delimit the beginning and end of the
transmission.
 Address: For PPP, uses the 8-bit broadcast address, "11111111".
 Frame Check Sequence (FCS): An 8-bit remainder from a cyclic redundancy
check (CRC) calculation, used for bit error detection.
The Internet Layer
The Internet Protocol (RFC 791), provides services that are roughly equivalent
to the OSI Network Layer. IP provides a datagram (connectionless) transport
service across the network. This service is sometimes referred to
as unreliable because the network does not guarantee delivery nor notify the
end host system about packets lost due to errors or network congestion. IP
datagrams contain a message, or one fragment of a message, that may be up to
65,535 bytes (octets) in length. IP does not provide a mechanism for flow
control.
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IP Packet Header Format

IP Addresses
IP (version 4) addresses are 32 bits in length (Figure 5). They are typically written
as a sequence of four numbers, representing the decimal value of each of the
address bytes. Since the values are separated by periods, the notation is
referred to as dotted decimal. A sample IP address is 208.162.106.17.
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IP Address Format

The Transport Layer Protocols
The TCP/IP protocol suite comprises two protocols that correspond roughly to the
OSI Transport and Session Layers; these protocols are called the Transmission
Control Protocol and the User Datagram Protocol (UDP)
TCP
 TCP, described in RFC 793, provides a virtual circuit (connection-oriented)
communication service across the network. TCP includes rules for formatting
messages, establishing and terminating virtual circuits, sequencing, flow
control, and error correction. Most of the applications in the TCP/IP suite
operate over the reliable transport service provided by TCP.
 The TCP data unit is called a segment; the name is due to the fact that TCP
does not recognize messages, per se, but merely sends a block of bytes from the
byte stream between sender and receiver.
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TCP segment format

UDP
UDP is described in RFC 768, provides an end-to-end datagram (connectionless)
service. Some applications, such as those that involve a simple query and
response, are better suited to the datagram service of UDP because there is no
time lost to virtual circuit establishment and termination. UDP's primary
function is to add a port number to the IP address to provide a socket for the
application.
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UDP Datagram Format

 Subnetting:
Lets work by Example.
Example 1: A service provider has given you the Class C network range 209.50.1.0.
Your company must break the network into 20 separate subnets.
Step 1) Determine the number of subnets and convert to binary
- In this example, the binary representation of 20 = 00010100.
Step 2) Reserve required bits in subnet mask and find incremental value
- The binary value of 20 subnets tells us that we need at least 5 network bits to
satisfy this requirement (since you cannot get the number 20 with any less than
5 bits – 10100)
- Our original subnet mask is 255.255.255.0 (Class C subnet)
- The full binary representation of the subnet mask is as follows:
255.255.255.0 = 11111111.11111111.11111111.00000000
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We must “convert” 5 of the client bits (0) to network bits (1) in order to satisfy the
requirements:
New Mask = 11111111.11111111.11111111.11111000
- If we convert the mask back to decimal, we now have the subnet mask that will
be used on all the new networks – 255.255.255.248
- Our increment bit is the last possible network bit, converted back to a binary
number:
New Mask = 11111111.11111111.11111111.1111(1)000 – bit with the parenthesis is your
increment bit. If you convert this bit to a decimal number, it becomes the
number „8‟
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Step 3) Use increment to find network ranges
- Start with your given network address and add your increment to the subnetted
octet:
209.50.1.0
209.50.1.8
209.50.1.16
…etc
- You can now fill in your end ranges, which is the last possible IP address before
you start the next range
209.50.1.0 – 209.50.1.7
209.50.1.8 – 209.50.1.15
209.50.1.16 – 209.50.1.23
…etc
- You can then assign these ranges to your networks. Remember the first and last
address from each range (network / broadcast IP) are unusable
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Example 1: A service provider has given you the Class C network range 209.50.1.0.
Your company must break the network into as many subnets as possible as long
as there are at least 50 clients per network.
Step 1) Determine the number of clients and convert to binary
- In this example, the binary representation of 50 = 00110010
Step 2) Reserve required bits in subnet mask and find incremental value
- The binary value of 50 clients tells us that we need at least 6 client bits to satisfy
this requirement (since you cannot get the number 50 with any less than 6 bits
– 110010)
- Our original subnet mask is 255.255.255.0 (Class C subnet)
- The full binary representation of the subnet mask is as follows:
255.255.255.0 = 11111111.11111111.11111111.00000000
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We must ensure 6 of the client bits (0) remain client bits (save the clients!) in
order to satisfy the requirements. All other bits can become network bits:
New Mask = 11111111.11111111.11111111.11 000000 note the 6 client bits that we have
saved
- If we convert the mask back to decimal, we now have the subnet mask that will
be used on all the new networks – 255.255.255.192
- Our increment bit is the last possible network bit, converted back to a binary
number:
New Mask = 11111111.11111111.11111111.1(1)000000 – bit with the parenthesis is your
increment bit. If you convert this bit to a decimal number, it becomes the
number „64‟
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Step 3) Use increment to find network ranges
- Start with your given network address and add your increment to the subnetted
octet:
209.50.1.0
209.50.1.64
209.50.1.128
209.50.1.192
- You can now fill in your end ranges, which is the last possible IP address before
you start the next range
209.50.1.0 – 209.50.1.63
209.50.1.64 – 209.50.1.127
209.50.1.128 – 209.50.1.191
209.50.1.192 – 209.50.1.255
- You can then assign these ranges to your networks. Remember the first and last
address from each range (network / broadcast IP) are unusable
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 When subnetting based on the number of
networks, SUBTRACT 1 from the number
 When subnetting based on the number of hosts
per network, ADD 1 to the number
 Follow these rules and you'll always be safe.
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Exploring the Functions of Routing
 we are going to explore the packet delivery process, from the routing
perspective. We will see how one of the main functions of routing is to
determine the optimal path across a routed network for IP packets.
Routers:
Routers implement layer 3 or network layer functions. Their main job is to
forward packets based upon a routing table. When doing so, they also provide
traffic segmentation, multiple broadcast domains, and define network layer
addressing subnets and networks. Those networks are defined by router
network adapters or ports to which IP addresses are assigned. Those IP
addresses are typically the default gateway to PCs and servers or other
networking devices. Routers also connect to service providers and act as
gateways to other networks, typically found at the perimeter or edge of the
network. Some of those network adapters will be other than Ethernet. They
will have connectivity to serial interfaces, DSL connections, and other forms of
WAN
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Routers
Router Functions
The basic routing function can be split into two areas; one is to build a
map of the network and for that routers typically use either static
routing or dynamic routing protocols. With the help of dynamic routing
protocols, routers will let other network devices know about not only the
topology of the network but also about network changes. Static routing
will be that static and will not adapt to network changes. Both models
accomplish the task of building the map of the network in the form of
the routing table.

 The command and output shown here display the routing table on a Cisco
router. With show IP route, an IOS device like this one could show the different
destinations, the cost to get there, what is known as the administrative distance
to define priorities for different routing protocols, and the next-hop to get to
that destination. Notice how the routing protocol that learned that particular
entry or destination is shown there in the first column. This is EIGRP, this is
RIP, and this is OSPF. With this information, routers will be able to determine
where to forward packets. They will do so by sending the packet to the next
router in the path according to the info in the routing table. Notice then that
routing is based on destination addresses.
Path Determination
 During the process of path determination, the routers will consider multiple
alternatives to get to the same place; those alternatives result from the
redundancy built into most network designs. You want multiple paths, so that
if one goes down, other alternatives will become available. In determining the
best path, routers will consider several things. One of them is the source of the
information, and so you could have multiple dynamic routing protocols or even
static routing populating the routing table and telling the router what the
options are.
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 The second piece of information is the cost of taking each path, and knowing
that the path is made up of multiple links or hops that are defined by other
routers. Then we could add the concepts of the cost in the context of the total
path, but that cost is nothing more than the sum of all the costs to reach each
hop in the path.
 Well, the two decisions are ruled by different pieces of information, for
example, in order to define a tie breaker between sources of information, the
routers use the administrative distance, so if a routing protocol like OSPF is
telling the router information on a destination and also RIP is telling that
router information on the same destination, then the administrative distance
will define who wins. Once the source is selected, then the cost is what matters;
in other words, if OSPF is giving me the information on those two paths, then
the cost of the path will define which one I take. This is similar to having two
maps to drive from one city to the other. You first select which map you are
going to follow and then if the map is giving you more than one option, then
you will select the option according to perhaps the amount of time it takes or
the amount of miles you have to drive for each option.
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Routing Tables
 So the routing table contains the network layer intelligence that tells the router
how to forward packets to remote destinations. Initially, that routing table is
made up of networks that are directly connected to the particular router. They
are obviously shown as directly connected networks, after that the way to learn
about remote destinations is by either populating the routing table with static
routes in which an administrator will tell the router how to get to the
destination or by populating the routing table via routing table advertisements
coming from other routers.
 So routers are gossipy and they will tell each other information that allows
them to know about all the gossip in the network. In both cases, static and
dynamic routing notice how routers use the reserved subnet addresses or
network addresses that contain all 0s in the host portion of the IP address.
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 In this case, we are talking about a classless subnetted class A address. Network
10 split into subnets similar to a class C. However, in all cases here, the host
portion of the address, the fourth byte is all 0s and that represents that subnet
or network itself. In other words, these are destination networks or subnets. In
the case of remote destinations, the routing table entries show what the next
hop is in order to reach that destination. In this case, in order to reach 10.1.3.0,
our next-hop is router 2 at 10.1.2.2.
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 These are categories of routing table entries that could be populated either
dynamically or statically. Some of them are born with the router. As soon as the
router boots up, it will identify its directly connected active networks and
interfaces and define them as reachable destinations, only because of the fact
that the router is directly attached or connected to it. Now that is pretty smart,
but even smarter is the fact that the routers will communicate with each other,
exchange routing information via dynamic routing protocols like OSPF or
EIGRP, and then learn not only about those destinations, but also adjust to
changes on those destinations.
 Routing protocols will be able to identify topology changes and tell each other
about them. Soon enough, entries will appear and disappear from the routing
table according to availability; again, an administrator could come in and
manually insert static entries. This is sometimes not recommended because
they will be static and they will not adjust to network changes; in other words,
if the entry or the destination goes down, the entry will remain there and the
router will still forward packets to a destination that is not available.
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 Perhaps a special case of a static route is the default route. Although they can
also be learned dynamically, static defaults are used when no explicit route to a
destination is known and so this is the entry that identifies all unknown
destinations. The router will say, "If I do not know about a certain destination, I
will forward a packet to someone that does, typically another router.
Routing Metrics
 Optimal path selection depends on what is known as the cost to reach a
destination across a certain path. Again, the cost of a path is made up of
incremental costs for each hop along the path. The cost is also known as
metric, and different routing protocols will consider different criteria in order
to define the metric. Older technologies and protocols consider the number of
routers along the path in order to reach a destination; that is what they call the
hop count. Hop count is sometimes not an efficient way to determine cost,
because you could have different bandwidths associated with each hop or each
link.
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Router Cost Path Factors

 In this example the two-hop path is better, because it has more bandwidth
available. Other routing protocols start considering bandwidth as a measure of
cost, and even more parameters in the criteria, for example, EIGRP considers
bandwidth delay, reliability, load, and maximum transmission unit. In that
case, a path with enough bandwidth, but one that is fully congested, would not
be selected and perhaps another path with less available bandwidth would be
selected because it is less congested and more reliable.
 Perhaps one of the points and highlights of this lesson is the fact that routing
protocol selection, if you are doing dynamic routing, is key in determining the
cost or metric and, therefore, how efficient and optimal the path selection will
be, but also the convergence time, which is defined by the time it takes for
routing protocol to detect a topology change and adjust by selecting an
alternative path if the main path is down. There are different categories of
routing protocols if you are using dynamic routing that define their cost and
metric, but also their behavior under those circumstances.
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Distance Vector Routing Protocols
 Perhaps one of the points and highlights of this lesson is the fact that routing
protocol selection, if you are doing dynamic routing, is key in determining the
cost or metric and, therefore, how efficient and optimal the path selection will
be, but also the convergence time, which is defined by the time it takes for
routing protocol to detect a topology change and adjust by selecting an
alternative path if the main path is down. There are different categories of
routing protocols if you are using dynamic routing that define their cost and
metric, but also their behavior under those circumstances.
 Using the distance vector approach, which is one of the categories, routers do
not have to really know the whole path toward the destination. They only have
to know the direction or vector in which to send a packet. In that sense, it will
only keep information in the routing tables related to what the next-hop
should be in order to reach a certain destination.
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Link-State Routing Protocols
 Link-State protocols are more efficient and effective in creating network
topologies, sharing them, and selecting the best path as compared to distance
vector protocols. There are several differences between the two categories. For
example, link state protocols will not broadcast the information per router, it
will use multicast where each router advertises via that multicast the link it
knows to the neighbors. Secondly, link-state protocols do not advertise
periodically. After an initial flood of all the information, yet will only advertise
changes to the topology. In other words, if the link goes down then that small
change will be advertised via multicast. Third, router not only know about the
next hop toward a destination, they know about the whole topological map of
the network. Each router after the initial flood will build that map of the
network, which includes all the routers and all the links. With that
information, each router is capable of browsing those tables via using the
shortest path first algorithm, and select the best path toward each destination.
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Configuring a Cisco Router
Here i will provide you some basic commands to set up your router .
More details on each topic will be coming in following lessons.
The Cisco IOS software provides access to several different command modes.
Each command mode provides a different group of related commands.
For security purposes, the Cisco IOS software provides two levels of access to
commands: user and privileged. The unprivileged user mode is called user EXEC
mode. The privileged mode is called privileged EXEC mode and requires a
password. The commands available in user EXEC mode are a subset of the
commands available in privileged EXEC mode.
The following table in the next slides describes some of the most commonly used
modes, how to enter the modes, and the resulting prompts. The prompt helps
you identify which mode you are in and, therefore, which commands are
available to you
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Cisco Router Mode

User EXEC Mode:
 When you are connected to the router, you are started in user EXEC mode. The
 user EXEC commands are a subset of the privileged EXEC commands.
Privileged EXEC Mode:
 Privileged commands include the following:
 Configure – Changes the software configuration.
 Debug – Display process and hardware event messages.
 Setup – Enter configuration information at the prompts.
 Enter the command disable to exit from the privileged EXEC mode and return
to
 user EXEC mode.
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Configuration Mode
 Configuration mode has a set of sub modes that you use for modifying
interface
 settings, routing protocol settings, line settings, and so forth. Use caution with
 configuration mode because all changes you enter take effect immediately.
 To enter configuration mode, enter the command configure terminal and exit
by pressing Ctrl-Z
Getting Help
 In any command mode, you can get a list of available commands by entering a
 question mark (?).
 Router>?
 To obtain a list of commands that begin with a particular character sequence,
 type in those characters followed immediately by the question mark (?).
 Router#co?
 configure connect copy
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 To list keywords or arguments, enter a question mark in place of a keyword or
 argument. Include a space before the question mark.
 Router#configure ?
 memory Configure from NV memory
 network Configure from a TFTP network host
 terminal Configure from the terminal
 You can also abbreviate commands and keywords by entering just enough
 characters to make the command unique from other commands. For example,
 you can abbreviate the show command to sh.
Configuration Files
 Any time you make changes to the router configuration, you must save the
 changes to memory because if you do not they will be lost if there is a system
 reload or power outage. There are two types of configuration files: the running
 (current operating) configuration and the startup configuration.
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 Use the following privileged mode commands to work with configuration files.
 configure terminal – modify the running configuration manually from the
terminal.
 show running-config – display the running configuration.
 show startup-config – display the startup configuration.
 copy running-config startup-config – copy the running configuration to the
startup configuration.
 copy startup-config running-config – copy the startup configuration to the
running configuration.
 erase startup-config – erase the startup-configuration in NVRAM.
 copy tftp running-config – load a configuration file stored on a
Trivial File Transfer Protocol (TFTP) server into the running configuration.
 copy running-config tftp – store the running configuration on a TFTP server.
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IP Address Configuration
Take the following steps to configure the IP address of an interface.
Step 1: Enter privileged EXEC mode:
 Router>enable password
Step 2: Enter the configure terminal command to enter global configuration
mode.
 Router#config terminal
Step 3: Enter the interface type slot/port (for Cisco 7000 series) or interface
 type port (for Cisco 2500 series) to enter the interface configuration mode.
 Example:
 Router (config)#interface ethernet 0/1
Step 4: Enter the IP address and subnet mask of the interface using the ip
 address ipaddress subnetmask command.
 Example,
 Router (config-if)#ip address 192.168.10.1 255.255.255.0
 Step 5: Exit the configuration mode by pressing Ctrl-Z
 Router(config-if)#[Ctrl-Z]
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Here is an example of configuring a serial port with an IP address:
switchA#config
switchA (config)#interface serial 1/1
switchA (config-if)#ip address 192.168.155.2 255.255.255.0
switchA (config-if)#ipv6 address fe80::230:1bff:fe80:b8ea/64
switchA (config-if)#ipv6 enable
switchA (config-if)#no shutdown
switchA (config-if)#ctrl-Z
Then to verify configuration:
switchA #show interface serial 1
In the Cisco IOS, the way to reverse or delete the results of any command is to
simply put no in front of it. For instance, if we wanted to unassign the IP
address we had assigned to interface serial 1/1:
switchA(config)#interface serail 1/1
switchA (config-if)#no ip address 192.168.155.2 255.255.255.0
switchA(config-if)ctrl-Z
switchA #show interface serial 1/1
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To create a static route, the administrator tells the router operating system that
any network traffic destined for a specified network layer address should be
forwarded to a similiarly specified network layer address. In the Cisco IOS this
is done with the ip route and ipv6 route commands.
switchA #config
switchA(config)#ip route 172.16.0.0 255.255.255.0 192.168.150.1
switchA(config)#ctrl-Z
switchA #show ip route
switchA #config
switchA(config)#ipv6 route fe80::230:1bff:fe80::/64 fe80::230:1bff:fe80::1
switchA(config)#ctrl-Z
switchA #show ipv6 route
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Routing Protocol Configuration
Routing Information Protocol (RIP)
mode.
Router#config terminal
Step 3: Enter the router rip command
 Router(config)#router rip
Step 4: Add the network number to use RIP and repeat this step for all the
 numbers.
 Router(config-router)#network network-number
Example: Router(config-router)#network 192.168.10.0
To turn off RIP, use the no router rip command.
 Router(config)#no router rip
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Other useful commands
 Specify a RIP Version
By default, the software receives RIP version 1 and version 2 packets, but sends
only version 1 packets. To control which RIP version an interface sends, use one
of the following commands in interface configuration mode:
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To control how packets received from an interface are processed, use one of the
following commands:
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Enable or Disable Split Horizon
Use one of the following commands in interface configuration mode:

Open Shortest Path First (OSPF)
mode.
 Router#config terminal
Step 3: Enter the router ospf command and follow by the process-id.
 Router(config)#router ospf process-id
Pick the process-id which is not being used. To determine what ids are being
used, issue the show process command.
 Router(config)#show process
Step 4: Add the network number, mask and area-id
 Router(config-router)#network network-number mask area area-id
The network-number identifies the network using OSPF. The mask tells which bits to use
from the network-number, and the area-id is used for determining areas in an OSPF
configuration.
Example:
 Router(config-router)#network 192.168.10.0 255.255.255.0 area 0.0.0.0
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Repeat this step for all the network numbers.
To turn off OSPF, use the following command.
 Router(config)#no router ospf process-id
Configure OSPF Interface Parameters
You are not required to alter any of these parameters, but some interface parameters must be
consistent across all routers in an attached network. In interface configuration mode,
specify any of the following:
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Interior Gateway Routing Protocol (IGRP)
Create the IGRP Routing Process
To create the IGRP routing process, use the following required commands starting in global
configuration mode:-
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Disable Holddown
The holddown mechanism is used to help avoid routing loop in the network, but
has the effect of increasing the topology convergence time.
To disable holddowns with IGRP, use the following command in router
configuration mode. All devices in an IGRP autonomous system must be
consistent in their use of holddowns.
Commands: No metric holddown

Enforce a Maximum Network Diameter
Define a maximum diameter to the IGRP network. Routes whose hop counts
exceed this diameter are not advertised. The default maximum diameter is 100 hops. The
maximum diameter is 255 hops.
 Use the following command in router configuration mode.
metric maximum-hops hops
To turn off IGRP, use the following command-
Router(config)#no router igrp autonomous-system
Border Gateway Protocol (BGP)
Enable BGP Routing
Use the following commands in global configuration mode.
router bgp autonomoussystem ---- Enable a BGP routing process, which places you in
router configuration mode.
network network-number[mask network-mask] [routemap route-map-name]—
Flag network as local to this autonomous system and enter it to the BGP table.
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Configure BGP Neighbors
BGP must completely understand the relationships it has with its neighbors.
Command: neighbor{ip-address | peergroup-name}remote-as number
-- Specify a BGP neighbour.
Reset BGP Connections
Use either of the following commands in EXEC mode to reset BGP connections
clear ip bgp address -- Reset a particular BGP connection.
clear ip bgp *-- Reset all BGP connections.
To turn off BGP, use the following command.
Router(config)#no router bgp autonomous-system
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Lessons Learned:
 TCP/IP Protocol Structure
 Subnetting
 Functions of Router
 Configuring Cisco Router
8/2/2013

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Presentation 3 for Students of professordkinney.com