Jaringan Komputer - Dr. Tb. Maulana Kusuma

Report
Internet dan Jaringan Komputer
PENGANTAR TCP/IP DAN
ROUTING
Dr. Tb. Maulana Kusuma
[email protected]
http://staffsite.gunadarma.ac.id/mkusuma
Magister Manajemen Sistem Informasi
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Internet Protocol
(IP)
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IP Addressing Basics
Symbolic names are easier to remember a string, such
as www.course.com, than a numeric address, such as
199.95.728—computers are the opposite
They deal with network addresses in the form of bit
patterns that translate into decimal numbers
IP uses a three-part addressing scheme, as follows:

Symbolic

Logical numeric

Physical numeric
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IP Addressing Basics
In keeping with the layered nature of network models, it
makes sense to associate the MAC layer address with
the Data Link layer (or TCP/IP Network Access layer, if
you prefer to think in terms of that model), and to
associate IP addresses with the Network layer (or the
TCP/IP Internet layer)
As data moves through intermediate hosts between the
original sender and the ultimate receiver, it does so
between pairs of machines, where each pair resides on
the same physical network
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IP Addressing Basics
At the Network layer, the original sender’s address is
represented in the IP source address field in the IP
packet header, and the ultimate recipient’s address is
represented in the IP destination address field in the
same IP packet header
The IP destination address value, in fact, is what drives
the sometimes-long series of intermediate transfers, or
hops, which occur as data makes its way across a
network from sender to receiver
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Anatomy of an IP Address
Numeric IP addresses use dotted decimal notation when
expressed in decimal numbers, and take the form
n.n.n.n., in which n is guaranteed to be between zero
and 255 for each and every value
The numeric values in dotted decimal representations of
numeric IP addresses are usually decimal values, but
may occasionally appear in hexadecimal (base 16) or
binary (base 2) notation
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Anatomy of an IP Address
Duplication of numeric IP addresses is not allowed
because that would lead to confusion
Also, there is a notion of “neighborhood” when it comes
to interpreting numeric IP addresses
Proximity between two numeric IP addresses (especially
if the difference is only in the rightmost one or two
octets) can sometimes indicate that the machines to
which those addresses correspond reside close enough
together to be on the same general network, if not on the
same physical cable segment
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IP Address Classes
Initially, these addresses were further subdivided into
five classes, from Class A to Class E
For the first three classes of addresses, divide the octets
as follows to understand how they behave:
Class A
n
Class B
n.n
Class C
n.n.n
h.h.h
h.h
h
If more than one octet is part of the network or host
portion of the address, then the bits are simply
concentrated to determine the numeric address
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IP Address Classes
The network portion of that address is 10, whereas the
host portion is 12.120.2, treated as a three-octet number
Address Classes D and E are for special uses
Class D addresses are used for multicast
communications, in which a single address may be
associated with more than one network host machine
This is useful only when information is broadcast to more
than one recipient at a time so it should come as no
surprise that video and teleconferencing applications, for
example, use multicast addresses
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More About Class A Addresses
Expressed in binary form (ones and zeroes only), Class
A addresses always take the form:
0bbbbbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb
The leading digit is always zero, and all other digits can
be either ones or zeroes
On any IP network, addresses consisting of all zeroes
and all ones are reserved for special uses, so of those
128 possible network addresses, only those from
00000001 to 01111110 (or 1 to 126, in decimal terms) are
considered usable
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More About Class A Addresses
The address for network 10 is reserved for private
network use
Also, by convention, the address 127.n.n.n is reserved
for loopback testing (or checking the integrity and
usability of a TCP/IP protocol stack installed on any
computer
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More About Class B Addresses
Class B addresses always take the form:
10bbbbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb
The leading two digits are 10, and the remaining digits
can be either ones or zeroes
RFC 1918 stipulates that 16 Class B addresses, from
172.16.0.0 to 172.32.255.255, are reserved for private
use
This means that the maximum number of public IP
addresses for Class B is 16,382-16, or 16,366
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Class B Address Facts and
Figures
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More About Class C Addresses
Class C addresses always take the form:
110bbbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb
The leading three digits are 110, and the remaining digits
can be either ones or zeroes
Note that this scheme reduces the total number of
networks possible by the most significant three bits
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More About
Address Classes D and E
Class D addresses always take the form:
1110bbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb
Class E addresses always take the form:
11110bbb.bbbbbbbb.bbbbbbbb.bbbbbbbbb
Class D is used for multicast addresses so that multiple
users can “share” a single IP address and receive the
same broadcast across a network from a single
transmission
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The Vanishing IP Address
Space
IP addresses were assigned for public use, they were
assigned on a per-network basis
With the ever-increasing demand for public IP addresses
for Internet access, it should come as no surprise that,
as early as the mid-1990s, experts began to predict that
the Internet would “run out” of available IP addresses
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The Vanishing IP Address
Space
The causes for concern have abated somewhat, Here’s why:
 The technocrats at the IETF introduced a new way to
carve up the IP address space—Classless Inter-Domain
Routing (CIDR)
 A brisk trade in existing IP network addresses sprung up
during the same time
 RFC 1918 reserves three ranges of IP addresses for
private use—a single Class A (10.0.0.0-10.255.255.255),
16 Class Bs (172.16.0.0-172.31.255.255), AND 256 Class
Cs (192.168.0.0-192.168.255.255). When used in tandem
with a technology called Network Address Translation
(a.k.a NAT), private IP addresses can help lift the “cap” on
public IP addresses
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IP Networks, Subnets, and
Masks
If two network interfaces are on the same physical
network, they can communicate directly with one another
at the MAC layer
In fact, each of the three primary IP address classes—
namely A, B, and C—also has an associated default
subnet mask
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IP Subnets and Supernets
A subnet mask is a special bit pattern that “blocks off” the
network portion of an IP address with an all-ones pattern
The reason why concepts like subnets and supernets
are important for TCP/IP networks is because each of
these ideas refers to a single “local neighborhood” on
such a network, seen from a routing perspective
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IP Subnets and Supernets
Thus, a subnet mask that is larger than the default mask
for the address in use divides a single network IP
address into multiple subnetworks
The network prefix identifies the number of bits in the IP
address, counting from the left that represents the actual
network address itself, and the additional two bits of
subnetting represent the bits that were borrowed from
the host portion of that IP address to extend the network
portion
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IP Subnets and Supernets
The entire network address, including the network prefix
and the subnetting bits, is called the extended network
prefix
This activity of stealing bits from the host portion of
further subdivide the network portion of an address is
called subnetting a network address, or subnetting
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IP Subnets and Supernets
When a computer on one subnet wishes to communicate
with a computer on another subnet, traffic must be
forwarded from the sender to a nearby IP gateway to
send the message on its way from one subnet to another
Supernetting takes the opposite approach: by combining
contiguous network addresses, it steals bits from the
network portion and uses them to create a single, larger
contiguous address space for host addresses
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Calculating Subnet Masks
The simplest form of subnet masking uses a technique
called constant-length subnet masking (CLSM), in which
each subnet includes the same number of stations and
represents a simple division of the address space made
available by subnetting into multiple equal segments
Another form of subnet masking uses a technique called
variable-length subnet masking (VLSM) and permits a
single address to be subdivided into multiple subnets, in
which subnets need not all be the same size
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Calculating Supernets
Supernets “steal” bits from the network portion of an IP
address to “lend” those bits to the host part
As part of how they work, supernets permit multiple IP
network addresses to be combined and make them
function together as if they represent a single logical
network
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Classless Inter-Domain Routing
(CIDR)
CIDR gets its name from the notion that it ignores the
traditional A, B, and C class designations for IP
addresses, and can therefore set the network-host ID
boundary wherever it wants to, in a way that simplifies
routing across the resulting IP address spaces
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Classless Inter-Domain Routing
(CIDR)
Creating a CIDR address is subject to the following
limitations:
 All the addresses in the CIDR address must be
contiguous
 When address aggregation occurs, CIDR address
blocks work best when they come in sets that are
greater than one, and equal to some lower-order bit
pattern that corresponds to all ones
 CIDR addresses are commonly applied to Class C
addresses
 To use a CIDR address on any network, all routers in
the routing domain must “understand” CIDR notation
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CIDR Notation
CIDR notation of an IP address:
192.0.2.0/18
"18" is the prefix length. It states that the first 18 bits are the
network prefix of the address (and 14 bits are available for
specific host addresses)
CIDR notation can replace the use of subnetmasks (but is more
general)

IP address 128.143.137.144 and subnetmask 255.255.255.0
becomes 128.143.137.144/24
CIDR notation allows to drop traling zeros of network addresses:
192.0.2.0/18 can be written as 192.0.2/18
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CIDR address blocks
CIDR notation can nicely express blocks of addresses
Blocks are used when allocating IP addresses for a company and for routing tables
(route aggregation)
CIDR Block Prefix
/27
/26
/25
/24
/23
/22
/21
/20
/19
/18
/17
/16
/15
/14
/13
# of Host Addresses
32
64
128
256
512
1,024
2,048
4,096
8,192
16,384
32,768
65,536
131,072
262,144
524,288
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Public Versus Private IP
Addresses
The private IP address ranges may be
expressed in the form of IP network
addresses, as shown in Table 2-4
Private IP addresses have one other
noteworthy limitation
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Public Versus Private IP
Addresses
Some IP services require what’s called a secure end-toend connection—IP traffic must be able to move in
encrypted form between the sender and receiver without
intermediate translation
Most organizations need public IP addresses only for
two classes of equipment:
 Devices that permit organizations to attach networks
to the Internet
 Servers that are designed to be accessible to the
Internet
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Managing Access
to IP Address Information
Although use of private IP addresses mandates NAT or a
similar address substitutions or masquerade capability,
some organizations elect to use address substitutions or
masquerade even when they use perfectly valid public IP
addresses on their internal networks
Proxy servers can provide what is sometimes called
reverse proxying
This permits the proxy server to front for servers inside
the boundary by advertising only the proxy server’s
address to the outside world, and then forwarding only
legitimate requests for service to internal servers for
further processing
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Obtaining Public IP Addresses
Unless you work for an organization that has
possessed its own public IP addresses since the
1980s (or acquired such addresses through merger
or acquisition), it’s highly likely that whatever public
IP addresses your organization uses were issued by
the very same ISP who provides your organization
with Internet access
Because all devices accessible to the Internet must
have public IP addresses, changing providers often
means going through a tedious exercise called IP
renumbering
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IP Addressing Schemes
To the uninitiated, it may appear that all these IP
addresses are randomly assigned, or perhaps generated
automatically by some computer somewhere
A great deal of thought has gone into the strategy for
allocating IP addresses around the world
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The Network Space
There are a number of critical factors that typically
constrain IP addressing schemes, and we look at these
in two groups
The first group of constraints determines the number and
size of networks
These are:
 Number of physical locations
 Number of network devices at each location
 Amount of broadcast traffic at each location
 Availability of IP addresses
 Delay caused by routing from one network to another
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IPv6 - IP Version 6
IP Version 6
 Is the successor to the currently used IPv4
 Specification completed in 1994
 Makes improvements to IPv4 (no revolutionary changes)
One (not the only !) feature of IPv6 is a significant increase in
of the IP address to 128 bits (16 bytes)
IPv6 will solve – for the foreseeable future – the
problems with IP addressing
1024 addresses per square inch on the surface of the
Earth.
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IPv6 Header
32 bits
ve rs ion
(4 bits )
Traffic Clas s
(8 bits )
Payload Le ngth (16 bits )
Flow Labe l
(24 bits )
Ne xt He ade r
(8 bits )
Hop Lim its (8 bits )
Source IP addre s s (128 bits )
De s tination IP addre s s (128 bits )
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IPv6 vs. IPv4: Address
Comparison
IPv4 has a maximum of
232  4 billion addresses
IPv6 has a maximum of
2128 = (232)4  4 billion x 4 billion x 4 billion x 4 billion
addresses
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Notation of IPv6 addresses
Convention: The 128-bit IPv6 address is written as eight 16-bit integers
(using hexadecimal digits for each integer)
CEDF:BP76:3245:4464:FACE:2E50:3025:DF12
Short notation:
Abbreviations of leading zeroes:
CEDF:BP76:0000:0000:009E:0000:3025:DF12
 CEDF:BP76:0:0:9E
:0:3025:DF12
“:0000:0000:0000” can be written as “::”
CEDF:BP76:0:0:FACE:0:3025:DF12  CEDF:BP76::FACE:0:3025:DF12
IPv6 addresses derived from IPv4 addresses have 96 leading zero bits.
Convention allows to use IPv4 notation for the last 32 bits.
::80:8F:89:90  ::128.143.137.144
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IPv6 Provider-Based Addresses
The first IPv6 addresses will be allocated to a provider-based plan
010
Registry Provider Subscriber Subnetwork Interface
ID
ID
ID
ID
ID
Type: Set to “010” for provider-based addresses
Registry: identifies the agency that registered the address
The following fields have a variable length (recommeded length in “()”)
Provider: ID of Internet access provider (16 bits)
Subscriber: ID of the organization at provider (24 bits)
Subnetwork: ID of subnet within organization (32 bits)
Interface: identifies an interface at a node (48 bits)
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Transmission Control Protocol
(TCP)
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Understanding Connectionless
Transport Protocols
Connectionless protocols provide the simplest kind of
transport services because they simply package
messages, taken as is from the TCP/IP Application layer,
into datagrams
A datagram slaps a header onto the higher-layer data
and passes it to the IP layer, where that datagram is
fitted with an IP header and packetized, after which it
may be transmitted across the network
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Understanding Connectionless
Transport Protocols
This method is called best-effort delivery
UDP runs up to 40% faster than TCP, under some
conditions, because it does next to nothing
It’s also typical for connectionless protocols to handle the
following kinds of tasks:

Message checksum

Higher-layer protocol identification
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User Datagram Protocol (UDP)
It’s appropriate to provide the following detailed
description for UDP:
 No reliability mechanisms
 No delivery guarantees
 No connection handling
 Identifies Application layer protocol conveyed
 Checksum for entire message carried in UDP header
 No buffering services
 No segmentation
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UDP Header Fields and
Functions
UDP is defined in RFC 768
When the Protocol field of an IP header contains the
value 17 (0x11), the UDP header follows the IP header
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UDP Port Numbers and
Processes
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Understanding
Connection-Oriented Protocols
Connection-oriented protocols create a logical
connection directly between two peers on an
internetwork
Connection-oriented protocols track the transfer of data,
and ensure it arrives successfully through
acknowledgements and sequence number tracking
An acknowledgement is a positive response, indicating a
set of data arrived
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Understanding
Connection-Oriented Protocols
Connection-oriented peers use sequence number
tracking to identify the amount of data transferred, and
any out-of-order packets
Connection-oriented protocols have a timeout
mechanism that indicates when a host waited too long
for a communication, and such communication should be
assumed lost
Connection-oriented protocols also have a retry
mechanism that enables them to recover lost data by
retransmitting it a specified number of times
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Transmission Control Protocol
(TCP)
TCP offers connection-oriented services with
sequencing, error recovery, and a sliding window
mechanism
Because of TCP’s end-to-end reliability and flexibility,
TCP is the preferred transport method for applications
that transfer large quantities of data and require reliable
delivery services
TCP hosts create a virtual connection with each other
using a handshake process
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Transmission Control Protocol
(TCP)
TCP transfers data as a continuous stream of bytes, with
no knowledge of the underlying messages or message
boundaries that might be contained in that byte stream
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TCP Startup Connection
Process (TCP Handshake)
TCP offers a connection-oriented transport that begins
with a handshake between two hosts
One host initiates the handshake to another host to:
(a)
(b)
(c)
Ensure the destination host is available
Ensure the destination host is listening on the
destination port number
Inform the destination host of the initiator’s sequence
number so the two sides can track data as it is
transferred
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TCP Handshake Is
a Three-Packet Process
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TCP Connection Termination
The TCP
connection
termination
process
requires
four
packets
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TCP Sequence and
Acknowledgement Process
The sequence and acknowledgement process
guarantees that packets are ordered properly and
protects against missing segments
During the handshake process, each side of the
connection selects its own starting sequence number
During the TCP startup and teardown sequences, the
Sequence Number and Acknowledgement Number fields
increment by one, even though no valid data is sent or
received
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TCP Congestion Control
Congestion is the overloading of the network or a
receiver
Overloading a receiver occurs when the number of data
bytes is greater than the advertised window
The current window is always the lesser of what the
network and receiver can handle
When TCP data is received, it is placed in this TCP
buffer area
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TCP Congestion Control
TCP has four defined congestion control mechanisms to ensure the
most efficient use of bandwidth, and quick error and congestion
recovery
TCP supports windowing—the process of sending numerous data
packets in sequence without waiting for an intervening
acknowledgement
The four mechanisms, defined in detail in RFC 2581, are:

Slow start

Congestion Avoidance

Fast Retransmit

Fast Recovery
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Network Window and Receiver Window Determine
the Current Congestion Window Size
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TCP Congestion Control
Slow Start
When a TCP host starts up, the size of the congestion
window is not known
The initial value of the window being used is twice the
sender’s MSS setting
Congestion Avoidance
Once the window size has increased using the Slow
Start algorithm, if an error occurs (a timeout), the window
size is divided in half
Next, the Congestion Avoidance algorithm is used to
increase the window size in a linear manner
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TCP Congestion Control
Fast Retransmit / Fast Recovery
When an out-of-order data segment is received, the
receiver should immediately send duplicate ACKs
The Fast Recovery process dictates that when a host
receives three duplicate ACKs, it must immediately start
retransmitting the lost segments, without waiting for the
retransmission timer to expire
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TCP Header Fields and
Functions
You should recognize some characteristics of the TCP header,
such as the Source and Destination Port Number fields
The definitions for the Source Port Number Field and
Destination Port Number Field are the same as those for the
UDP fields
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Common and Appropriate Uses
for TCP and UDP
Given that TCP is robust and reliable, and UDP is not,
why would any Application layer protocol or service
choose UDP for transport when TCP is readily available?
The short answer to that question is overhead
For some lightweight services, such as messenger
service, TCP is overkill, and UDP is used instead
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Common and Appropriate Uses
for TCP and UDP
For applications, such as RIP, that rely on regular
updates of routing tables, and track timeout values as
part of ordinary behavior, the extra reliability of TCP isn’t
necessary, and UDP is used instead
TCP was designed in an era when 300-bps
communications was considered fast, and when noisy
lines or intermittent communications problems made
long-haul, reliable transmission of data inherently risky
without access to a robust, reliable transport service
TCP is a more important transport than UDP, and is still
used for the majority of TCP/IP Application layer
protocols and services
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Routing
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Understanding Routing
We start our discussion by explaining the routing table
This table is a database that lives in the memory of the
router
Entries in this database are known as “routes” and
consist of a network address, a “next hop” (routing
jargon for the IP address of the next router in the path to
the destination), various metrics, and vendor-specific
information
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Understanding Routing
A routing table is a compilation of all the networks that
the router can reach
The routing table is used as follows: When a packet is
received on a network interface, the first thing the router
must do is find out where the packet wants to go, so the
router reads the first field in the IP header, which is the
Destination Address, and then looks in the Network field
of its routing table for a match
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Understanding Routing
A route entry can be placed in a routing table in three
basic ways
The first way is through direct connection
The second is that it can be manually configured
The third way that an entry can be placed in a routing
table is dynamically, by using a routing protocol
Routers use routing protocols to share information about
the various networks on an internetwork
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Understanding Routing
Thus, you simply configure the protocol on each router,
and the routers will convey Network Layer Reachability
Information (NLRI) to each other
Routed protocols are Layer 3 protocols that are used to
get packets through an internetwork
There are two primary ways to group routing protocols
The first is by the method they use to communicate
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Understanding Routing
The two primary “flavors” employed by routing protocols
are distance vector and link-state
The routing protocols used inside a routing domain are
called Interior Gateway Protocols (IGPs), and the routing
protocols used to connect these routing domains are
known as Exterior Gateway Protocols (EGPs)
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Distance Vector Routing
Protocols
There are several distance vector routing protocols in
use today
The most popular by a wide margin is Routing
Information Protocol (RIP), followed by a Cisco
proprietary protocol called Interior Gateway Routing
Protocol (IGRP)
These protocols have several things in common that
distinguish them from link-state protocols
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Distance Vector Routing
Protocols
The second major distinction is that they “route by
rumor”
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Link-State Routing Protocols
Link-state routing protocols differ from distance vector
routing protocols in two primary ways
The first is that they do not router by rumor
The second major difference is that they do not
periodically broadcast their entire tables
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Link-State Routing Protocols
In this configuration, Routers A, B, and C send Hello
packets to Network 1
As they hear each other’s Hello packets, each router
builds an adjacencies database
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Areas, Autonomous
Systems, and Border Routers
Extremely large networks can be broken down into
regions called Autonomous Systems (ASs)
These Autonomous Systems are under the same
administrative control
The routers that connect Autonomous Systems are
called Autonomous System Border Routers (ASBRs)
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An Exterior Gateway Protocol Is Used
to Connect Two Autonomous Systems
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Interior Gateway Protocols
(IGPs)
Interior Gateway Protocols are used to exchange routing
information within an AS
These protocols are also referred to as intra-domain
routing protocols
The most commonly used IGPs are Routing Information
Protocol (RIP) (versions 1 and 2) and Open Shortest
Path First (OSPF)
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Enhanced Interior Gateway
Routing Protocol (EIGRP)
IGRP was developed in the 1980s by Cisco Systems in
an effort to provide a more efficient interior gateway
protocol
IGRP was updated in the early 1990s—the updated
version is called Enhanced Interior Gateway Routing
Protocol (EIGRP)
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Exterior Gateway Protocols
(EGPs)
Exterior Gateway Protocols are used to exchange
routing information between Autonomous Systems
These protocols are also referred to as inter-domain
routing protocols
Interestingly, the name Exterior Gateway Protocol was
assigned to the first implementation of this type of
routing
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Border Gateway Protocol (BGP)
BGP is a distance vector protocol and is the replacement
for EGP
The current version of BGP is version 4, which is defined
in RFC 1771
BGP offers three types of routing operations:

Inter-autonomous system routing

Intra-autonomous system routing

Pass-through autonomous system routing
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Typical BGP Design
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Border Gateway Protocol (BGP)
Figure 10-15 illustrates how BGP is used for interautonomous system routing
When BGP is configured for intra-autonomous system
routing, the BGP routers are located within the same AS
Pass-through autonomous system routing enables BGP
peer routers to exchange routing information across an
AS that does not support BGP
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