Transcript IPNetworkingUNIT7 - Rhema Impact Ministries

Unit 7
Advanced IP Routing
Chapter 19 to 21
© 2011 ITT Educational Services Inc.
NT-2640 Advanced Networking: Unit 7: Slide 1
Class Agenda 10/31/15
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Learning Objectives
Unit 7: Discussions and Video
Lab Activities will be done in class.
Assignments will be given in class.
Break Times. 10 Minutes break in every 1 Hour.
Note: Submit all Assignment and labs due
today.
Finding All Subnet IDs
• Given a single class A, B, or C network, and the single subnet
mask to use for all subnets, what are all the subnet IDs?
• When learning how to answer this question, you can think
about the problem in either binary or in decimal.
• The decimal process begins by identifying the first, or
numerically lowest, subnet ID. After that, the process identifies
a pattern in all subnet IDs for a given subnet mask, so that you
can find each successive subnet ID through simple addition.
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The First Subnet ID: The Zero Subnet
• The first step in finding all subnet IDs of one network is incredibly simple:
copy the network ID.
• That is, take the class A, B, or C network ID – in other words, the classful
network ID – and write it down as the first subnet ID.
• No matter what class A, B, or C network you use, and no matter what subnet
mask you use, the first (numerically lowest) subnet ID is equal to the network
ID.
• For example, if you begin with classful network 172.20.0.0, no matter what
the mask is, the first subnet ID is 172.20.0.0.
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Finding the Pattern Using the Magic Number
• Subnet IDs follow a predictable pattern, at least when using our assumption
of a single subnet mask for all subnets of a network.
• The pattern is equal to the magic number.
• To review, the magic number is 256, minus the mask’s decimal value, in a
particular octet that the book refers to as the interesting octet.
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Generic Subnets Chart
Table 18-1 Generic List-All-Subnets Chart
Octet
Mask
Magic Number
Network Number/Zero
Subnet
Next Subnet
Next Subnet
Last Subnet
Broadcast Subnet
Out of Range (Used by
Process)
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Finding the Magic Number
• Step 1. Write down the subnet mask, in decimal, in the first
empty row of the table.
• Step 2. Identify the interesting octet, which is the one octet of
the mask with a value other than 255 or 0. Draw a rectangle
around the column of the interesting octet.
• Step 3. Calculate and write down the magic number by
subtracting the subnet mask’s interesting octet from 256.
• Step 4. Write down the classful network number, which is the
same number as the zero subnet, in the next empty row of the
list-all-subnets chart.
© 2011 ITT Educational Services Inc.
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Finding the Magic Number
• Step 5. To find each successive subnet number:
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a. For the three uninteresting octets, copy the previous subnet number’s values.
b. For the interesting octet, add the magic number to the previous subnet
number’s interesting octet.
• Step 6. Once the sum calculated in Step 5b reaches
256, stop the process. The number with the 256 in it is
out of range, and the previous subnet number is the
broadcast subnet.
Results of First Four Steps: 172.16.0.0,
255.255.240.0
© 2011 ITT Educational Services Inc.
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Results on 172.16.0.0, 255.255.240.0
• Step 1. Record mask 255.255.240.0, which was given as part
of the problem statement.
• Step 2. The mask’s third octet is neither 0 nor 255, making the
third octet interesting.
• Step 3. Because the mask’s value in the third octet is 240, the
magic number = 256 – 240 = 16.
• Step 4. Because the network ID is 172.16.0.0, the first subnet
ID, the zero subnet, is also 172.16.0.0.
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List of Subnet IDs: 172.16.0.0, 255.255.240.0
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Results of First Four Steps: 192.168.1.0,
255.255.255.224
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List of Subnet IDs: 192.168.1.0, 255.255.255.224
© 2011 ITT Educational Services Inc.
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Check Point
1. Describe the magic number process
2. What is subnet ID or zero subnet?
3. What is the subnet zero for IP address
192.168.131.29/26?
© 2011 ITT Educational Services Inc.
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Objectives
In this unit, students will demonstrate an:
• Understanding of VLSM including Design and Subnetting Concepts
• Understanding of Route Summarization Concepts
• Understanding of the Host Networking Utilities for Troubleshooting IP
Networking Issues including “ping” and “traceroute”
• Understanding of Host & Router IP Routing Troubleshooting including
Commons Steps
• Understanding of OSPF including Neighbor Discovery and
Establishment, Topology Exchange and Route Selection Processes
• Understanding of OSPF Areas, Router Types, and Convergence
• Understanding of OSPF Configuration and Verification Steps
© 2011 ITT Educational Services Inc.
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VLSM
• VLSM occurs when an internetwork uses more than one mask
in different subnets of a single Class A, B, or C network.
• VLSM allows engineers to reduce the number of wasted IP
addresses in each subnet, allowing more subnets and avoiding
having to obtain another registered IP network number from
regional IP address assignment authorities.
• , even when using private IP networks (as defined in RFC
1918), large corporations might still need to conserve the
address space, again creating a need to use VLSM.
© 2011 ITT Educational Services Inc.
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Classless and Classful Routing Protocols
• For a routing protocol to support VLSM, the routing protocol must
advertise not only the subnet number but also the subnet mask when
advertising routes.
• A routing protocol must include subnet masks in its routing updates to
support manual route summarization.
• Each IP routing protocol is considered to be either classless or
classful , based on whether the routing protocol does (classless) or
does not (classful) send the mask in routing updates.
• Each routing protocol is either classless or classful by its very nature;
no commands exist to enable or disable whether a particular routing
protocol is a classless or classful routing protocol.
© 2011 ITT Educational Services Inc.
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Classless and Classful Interior IP Routing Protocols
Routing
Protoco Is It
l
Classless?
Sends
Mask in
Updates
Supports
VLSM
Supports Manual
Route
Summarization
RIP-1
No
No
No
No
IGRP
No
No
No
No
RIP-2
Yes
Yes
Yes
Yes
EIGRP
Yes
Yes
Yes
Yes
OSPF
Yes
Yes
Yes
Yes
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Manual Route Summarization
• Small networks might have only a few dozen routes in their routers’ routing
tables.
• The larger the network, the larger the number of routes.
• In fact, Internet routers have more than 100,000 routes in some cases.
• The routing table might become too large in large IP networks. As routing
tables grow, they consume more memory in a router.
• Also, each router can take more time to route a packet, because the router
has to match a route in the routing table, and searching a larger table
generally takes more time.
• And with a large routing table, it takes more time to troubleshoot problems,
because the engineers working on the network need to sift through more
information.
• Route summarization reduces the size of routing tables while maintaining
routes to all the destinations in the network.
© 2011 ITT Educational Services Inc.
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Route Summarization Concepts
• Engineers use route summarization to reduce the size of the
routing tables in the network.
• Route summarization causes some number of more-specific
routes to be replaced with a single route that includes all the IP
addresses covered by the subnets in the original routes.
• Summary routes, which replace multiple routes, must be
configured by a network engineer.
• Route summarization works much better when the network was
designed with route summarization in mind.
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Route Summarization Configuration
• Route summarization configuration differs with
different routing protocols; Enhanced IGRP (EIGRP) is
used.
• The summary routes for EIGRP are created by the ip
summary-address interface subcommands on
Yosemite and Seville in this case.
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Autosummarization And Manual summarization
• Manual route summarization can improve routing
efficiency, reduce memory consumption, and improve
convergence by reducing the length of routing tables.
• Automatic summarization of routes at the boundaries
of classful networks, uses a feature called
autosummarization.
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Autosummarization Support and Configuration
• Classful routing protocols must use autosummarization. Some classless
routing protocols support autosummarization, defaulting to use it, but with the
ability to disable it with the no auto-summary router subcommand.
• Below summarizes the facts about autosummarization on Cisco routers.
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Autosummarization Support and Defaults
Routing
Protocol
Classless?
Supports Autosummarization?
Defaults to Use
Autosummarization?1
Can Disable
Autosummarization?
RIP-1
No
Yes
Yes
No
RIP-2
Yes
Yes
Yes
Yes
EIGRP
Yes
Yes
Yes
Yes
OSPF
Yes
No
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© 2011 ITT Educational Services Inc.
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Chapter 20
“Troubleshooting II”
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The ping and traceroute Commands
• Internet Control Message Protocol (ICMP)
• TCP/IP includes ICMP, a protocol designed to help manage and control the
operation of a TCP/IP network.
• The ICMP protocol provides a wide variety of information about a network’s
health and operational status.
• Control Message is the most descriptive part of the name. ICMP helps
control and manage IP’s work by defining a set of messages and procedures
about the operation of IP.
• Therefore, ICMP is considered part of TCP/IP’s network layer. Because
ICMP helps control IP, it can provide useful troubleshooting information.
• In fact, the ICMP messages sit inside an IP packet, with no transport layer
header, so ICMP is truly an extension of the TCP/IP network layer.
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• The ping Command and the ICMP Echo Request and Echo Reply
• The ping command uses the ICMP Echo Request and Echo Reply
messages.
• When people say they sent a ping packet, they really mean that they sent an
ICMP Echo Request.
• These two messages are somewhat self-explanatory.
• The Echo Request simply means that the host to which it is addressed
should reply to the packet.
• The Echo Reply is the ICMP message type that should be used in the reply.
• The Echo Request includes some data that can be specified by the ping
command; whatever data is sent in the Echo Request is sent back in the
Echo Reply.
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The Ping Command
• The ping command lists various responses that in some cases
imply that an unreachable message was received.
ping Command Code
!
.
U
N
M
?
Description
ICMP Echo Reply received
Nothing was received before the ping command timed out
ICMP unreachable (destination) received
ICMP unreachable (network/subnet) received
ICMP Can’t Fragment message received
Unknown packet received
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The ICMP Time Exceeded Message
• The ICMP Time Exceeded message notifies a host when a
packet it sent has been discarded because it was “out of time.”
• Packets are not actually timed, but to prevent them from being
forwarded forever when there is a routing loop, each IP header
uses a Time to Live (TTL) field.
• Routers decrement the TTL by 1 every time they forward a
packet; if a router decrements the TTL to 0, it throws away the
packet.
• This prevents packets from rotating forever. Figure 7-3 shows
the basic process.
© 2011 ITT Educational Services Inc.
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TTL Decremented to 0
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The traceroute Command
• The ping command is a powerful troubleshooting tool that can be used to
answer the question “Does the route from here to there work?”
• The traceroute command provides an arguably better troubleshooting tool
because not only can it determine if the route works, but it can supply the IP
address of each router in the route.
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If the route is not working, traceroute can identify the best places to start troubleshooting
the problem.
The IOS traceroute command uses the Time Exceeded message and the IP TTL field to
identify each successive router in a route.
• The traceroute command sends a set of messages with increasing TTL
values, starting with 1.

The traceroute command expects these messages to be discarded when routers
decrement the TTL to 0, returning Time Exceeded messages to the traceroute command.
The source IP addresses of the Time Exceeded messages identify the routers that
discarded the messages, which can then be displayed by the traceroute command.
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show ip route Reference
• The show ip route command plays a huge role in troubleshooting IP
routing and IP routing protocol problems.
• Below shows the output of the show ip route command.
show ip route Command Output Reference
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Lab Activities.
• Complete 7 Lab in class.
• All answers to overdue labs should be
submitted in the next class.
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Assignment
• Unit 7 assignment will be given in class.
• Reading Assignment: Read chapter 22 and 23
© 2011 ITT Educational Services Inc.
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