Transcript Week_Eleven_Network_ppt - Computing Sciences

ITEC 275
Computer Networks – Switching,
Routing, and WANs
Week 11
Robert D’Andrea
2015
Agenda
• Learning Activities
– Industry Tests
– Build and Test a Prototype
– Write and Implement a Test Plan
– Tools for Testing a Network Design
– Multicasting
– QoS
– Queuing and Traffic Shaping
Reasons to Test
• Verify that the design meets key business and
technical goals
• Validate LAN and WAN technology and device
selections
• Verify that a service provider provides the agreedup service
• Identify bottlenecks or connectivity problems
• Determine optimization techniques that will be
necessary
Reasons to Test
• Proving that your network design is better than a
competing design
• Passing an “acceptance test” that gives you
approval to go forward with the network
implementation
• Reassure mangers and co-workers that your
design is effective
• Identifying any risks that might impede
implementation and planning for contingencies
• Determine how much additional testing might be
required. Will the new system be deployed as a
pilot and undergo additional testing before being
implemented
Testing Your Network Design
• Use industry testing services
• Build and test a prototype system
• Use third-party and Cisco tools
Respected Independent Test Labs
• The Interoperability Lab at the University of
New Hampshire (IOL)
• ICSA Labs
• Miercom Labs
• AppLabs
• The Tolly Group
• Penetration Testing test your network and
applications before the bad guys do.
Simple verses Complex Network
Designs
• Simple network designs can rely on test results from
vendors, independent labs, or trade journals to prove
to your customer that your design will perform as
intended.
• Complex network designs require more
considerations.
– Testing should be implemented in-house
– Testing will require more than component testing.
There will be a need for unit, integration, and
system testing.
Scope of a Prototype System
• Normally, it is impractical to implement a
full-scale network system.
• A prototype should verify important
capabilities and functions that might not
perform adequately.
• Risky functions include complex, intricate
functions and functions that were influenced
by the need to make tradeoffs with other
network components.
Live Production Network
• Perform initial testing during off-hours to
minimize issues with user community,
performance, and existing traffic flow.
• Perform final testing during normal hours and
benchmark the performance.
• Perform final testing at various times to
exercise the network during typical loads and
benchmark the performance.
Test Plan
What is a Test Plan?
Your test plan is primarily comprised of test cases
and test items. Think of a test case as a scenario or a
finite state in which your network might find itself.
In each test case, you'll have a list of test items or
functions or features that you want to evaluate. Each
test item should include not just an action, but the
success criteria, and if you want to get more
sophisticated, criticality. For example, you might want
to make sure a business-critical application still work
after a network change. So you'd arrange to have the
application owners create a transaction or operate the
application.
Components of a Test Plan
• Test objectives and acceptance criteria
• The types of tests that will be run
• Network equipment and other resources
required
• Testing scripts
• The timeline and milestones for the testing a
project
Components of a Test Plan
• Test objectives and acceptance criteria
Objectives and acceptance should be based on a
customer’s business and technical goals
Acceptance of test results are acceptable by both
the customer and the tester.
– Measure response time
– Measure applications throughput
– Measure the amount of time it takes to hear a dial
tone using Voice over IP
– Establish a baseline measurement of CRC errors
Test Objectives and Acceptance
Criteria
• Specific and concrete
• Based on business and technical goals
• Clear criteria for declaring that a test passed or
failed
• Avoid biases and preconceived notions about
outcomes
• If appropriate, reference an established
baseline
Test Plan Considerations
Network Connectivity Section
• Is Layer 2 set up appropriately? (VLANs on the right trunks,
PVCs, etc.)
• Do your router tables have the proper routes? (Check the next
hops and ages, too.)
• Can you ping everywhere in the network? (Performance: Are
the times acceptable?)
• Do traceroutes show paths you would expect?
If you load balance across the core of your network,
verify each link is being used.
• Is DHCP handing out addresses?
• DNS resolving names properly?
• Does your remote access still work?
Test Plan Considerations
Application Connectivity Section
• Does VOIP work? Is it showing up in the right
queues?
• Are your firewalls and proxies blocking and allowing
traffic appropriately?
• Can you browse the Web?
• Are your network management and logging systems
working?
• Do your business applications work? (And do
transactions complete in an acceptable time?)
• Are backup jobs still working?
Achieve Success with a New Network
Design
Your chances of success are much greater
if you perform several simple tests along the
way, rather than waiting until you think you're
done and discovering that something doesn't
work. Performing simple incremental tests along
the way help testers and customers maintain a
sense of truthfulness and confidence about in the
system being tested.
Types of Tests
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Application response-time tests with terminal
Throughput tests (I/O)
Availability tests (failure test)
Regression tests (does the network perform
similarly after changes were implemented)
Types of Tests
What is Protocol Testing?
• To understand the behavior of a protocol, it must be
tested to observe the protocol’s functionality
• Verify every phase of testing life cycle for
1. Functionality testing
2. Interoperability testing (IOT) is the process of
testing to determine the interoperability of a
software product
3. Performance
• Obtain tools to generate and test the protocol
messages
Types of Tests
Why is Protocol Testing required?
• Different vendor products need to communicate with
each other
• If any product is using this standards in their devices
they are interoperable with other vendor devices as
both must meet compliance to Standards of
IETF/RFC to study the network through their packet
data
• Protocol testing ensures proper functionality of
various elements of a message. It also ensures
whether it has designed as per specification.
Resources Needed for Testing
Test plan should include a network topology drawing for tester to
be able to reference.
A list of switches, routers, bridges, firewalls, servers, telephone
equipment, and wireless access points.
A list of documented version numbers for hardware and software.
• Scheduled time in a lab either at your site or the customer’s
site
• Power, air conditioning, rack space, and other physical
resources
• Help from co-workers or customer staff
• Help from users to test applications
• Network addresses and names
Resources Needed for Testing
How it is carried out?
Objective: To test the protocol
i.e. to check every node with their packet data.
Tools: Protocol Analyzer and simulator.
Example Test Script
Workstations
Server 1
Firewall
Network A
Network B
Protocol
Analyzer
Protocol
Analyzer
Example Test Script (continued)
• Test objective. Assess the firewall’s capability to
block Application ABC traffic, during both light
and moderately heavy load conditions.
• Acceptance criterion. The firewall should block
the TCP SYN request from every workstation on
Network A that attempts to set up an Application
ABC session with Server 1 on Network B. The
firewall should send each workstation a TCP RST
(reset) packet.
Example Test Script (continued)
1. Start capturing network traffic on the protocol
analyzer on Network A.
2. Start capturing network traffic on the protocol
analyzer on Network B.
3. Run Application ABC on a workstation located
on Network A and access Server 1 on Network
B.
4. Stop capturing network traffic on the protocol
analyzers.
Example Test Script (continued)
Display data on Network A’s protocol analyzer
and verify that the analyzer captured a TCP SYN
packet from the workstation. Verify that the network
layer destination address is Server 1 on Network B,
and the destination port is port 1234 (the port
number for Application ABC). Verify that the
firewall responded to the workstation with a TCP
RST packet.
5.
Example Test Script (continued)
6.
7.
8.
9.
Display data on Network B’s protocol analyzer and
verify that the analyzer did not capture any ApplicationABC traffic from the workstation.
Log the results of the test in the project log file.
Save the protocol-analyzer trace files to the project tracefile directory.
Gradually increase the workload on the firewall, by
increasing the number of workstations on Network A one
at a time, until 50 workstations are running Application
ABC and attempting to reach Server 1. Repeat steps 1
through 8 after each workstation is added to the test.
Example Test Script (continued)
Host A sends a TCP SYNchronize packet to Host B
Host B receives A's SYN
Host B sends a SYNchronize-ACKnowledgement
Host A receives B's SYN-ACK
Host A sends ACKnowledge
Host B receives ACK.
TCP socket connection is ESTABLISHED.
Tools for Testing a Network Design
• Network-management and monitoring tools.
These monitoring tools are used to alert
network management to problems and report
significant network problems.
• Traffic generation tools
• Modeling and simulation tools
• QoS and service-level management tools
• Protocol analyzer
• http://www.topdownbook.com/tools.html
Protocol Analyzer Tool
A protocol analyzer is used to analyze traffic
behavior, errors, utilization, efficiency, and rates of
broadcast and multicast packets.
A protocol analyzer can be a computer program
or a piece of computer hardware that can intercept
and log traffic passing over a digital network or part
of a network. As data streams flow across the
network, the sniffer captures each packet and, if
needed, decodes the packet's raw data, showing the
values of various fields in the packet, and analyzes
its content according to the appropriate RFC or
other specifications.
Simulation Tool
A simulation tool enables you to develop a
model of a network, estimate the performance of the
network and compare alternatives for implementing
the network.
iTrinegy Network Emulator (INE) products
enable you to realistically recreate a wide variety of
network conditions like latency, jitter, packet
loss/error/reordering and bandwidth restrictions so
that you can simulate environments such as Wide
Area Networks (WANs), Wireless LANs, GPRS,
3G, IP over Radio / Radio over IP(RoIP), Satellite
or MPLS networks.
Command Tools
Test Tools:
ipconfig
ping <IP address>
ping <DNS name>
tracert <DNS name>
nslookup <DNS name>
netstat
ping
ping yahoo.com
tracert yahoo.com
nslookup yahoo.com
netstat -a
Reasons to Optimize
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Meet key business and technical goals
Use bandwidth efficiently
Control delay and jitter
Reduce serialization delay
Support preferential service for essential
applications
• Meet Quality of Service (QoS) requirements
IP Multicast
Server
Server
IP Multicast
Router/MCS
The Miscellaneous Control Subsystem
(MCS) works with its companion Routing
Engine to provide control and monitoring
functions for router components. It also
generates a clock signal for the SONET/SDH
interfaces on the router.
IP Multicast
Applications
Applications that take advantage of
multicast include video conferencing, corporate
communications, distance learning, and
distribution of software, stock quotes, and news.
IP Multicast Helps Optimize Bandwidth
Usage
• With IP multicast, you can send a high-volume
multimedia stream just once instead of once
for each user
• Requires support for
– Multicast addressing
– Multicast registration (IGMP)
– Multicast routing protocols
IP Multicast Addresses
IPv4 Multicast Addresses
224.0.0.0 to 239.255.255.255
IPv6 Multicast Addresses
FF02:0:0:0:0:0:0:1 All Nodes Address
FF02:0:0:0:0:0:0:2 All Routers Address
IP Multicast Helps Optimize Bandwidth
Usage
To map an IP multicast address to a MAClayer multicast address, the low order 23 bits of
the IP multicast address are mapped directly to
the low order 23 bits in the MAC-layer multicast
address. Because the first 4 bits of an IP
multicast address are fixed according to the class
D convention, there are 5 bits in the IP multicast
address that do not map to the MAC-layer
multicast address.
IP Multicast Addressing
• Uses Class D multicast destination address
– 224.0.0.0 to 239.255.255.255
• Converted to a MAC-layer multicast
destination address
– The low-order 23 bits of the Class D address
become the low-order 23 bits of the MAC-layer
address
– The top 9 bits of the Class D address are not used
– The top 25 bits of the MAC-layer address are
0x01:00:5E followed by a binary 0
Internet Group Management Protocol
(IGMP)
• Allows a host to join a multicast group
• Host transmits a membership-report message
to inform routers on the segment that traffic for
a group should be multicast to the host’s
segment
• IGMPv2 has support for a router more quickly
learning that the last host on a segment has left
a group
Multicast Routing Protocols
• Becoming obsolete
– Multicast OSPF (MOSPF)
– Distance Vector Multicast Routing Protocol
(DVMRP)
• Still used
– Protocol Independent Multicast (PIM)
• Dense-Mode PIM
• Sparse-Mode PIM
Multicast Routing Protocols
Multicast Routing Protocols
What is PIM?
Protocol-Independent Multicast (PIM) is a
family of multicast routing protocol for Internet
Protocol (IP) networks that provide one-to-many and
many-to-many distribution of data over
a LAN, WAN or the Internet. It is termed protocolindependent because PIM does not include its
own topology discovery mechanism, but instead uses
routing information supplied by other routing
protocols.
PIM (Protocol Independent Multicast)
• Dense mode is used when there are many
members (employees listen to a company
president). PIM is similar to DVMRP. Both
use reverse-path forwarding (RPF) mechanism
to compute the shortest (reserve) path between
a source and all possible recipients of a
multicast packet.
• Dense PIM does not require the computation
of routing tables.
PIM (Protocol Independent Multicast)
What is PIM Dense Mode?
Dense mode PIM is the older and simpler
PIM mode. It works well in small networks
where there are a large number of listeners, but is
inefficient in larger network.
PIM Dense Mode
PIM Dense Mode
PIM (Protocol Independent Multicast)
• Sparse mode utilizes a rendezvous point (RP).
A rendezvous point provides a registration
service for a multicast group.
• Sparse mode PIM relies on IGMP which let a
host join a group by sending a membershipreport message, and detach from a group by
sending a leave message.
PIM (Protocol Independent Multicast)
PIM Sparse Mode (PIM-SM) explicitly
builds unidirectional shared trees rooted at
a rendezvous point (RP) per group, and
optionally creates shortest-path trees per source.
PIM-SM generally scales fairly well for widearea usage.
Serialization
What is serialization?
Serialization is the process of
translating data structures or object state into a
format that can be stored (for example, in a file
or memory buffer, or transmitted across
a network connection link) and reconstructed
later in the same or another computer
environment. When the resulting series of bits is
reread according to the serialization format, it
can be used to create a semantically identical
clone of the original object.
Serialization
• Transmission delay or serialization delay
In a network based on packet switching,
transmission delay (or store-and-forward delay) is
the amount of time required to push all of the
packet's bits into the wire. In other words, this is
the delay caused by the data-rate of the link.
Transmission delay is a function of the
packet's length and has nothing to do with the
distance between the two nodes. This delay is
proportional to the packet's length in bits.
Reducing Serialization Delay
• Link-layer fragmentation and interleaving
– Breaks up and reassembles frames
– Multilink PPP
– Frame Relay FRF.12
• Compressed Real Time Protocol
– RTP is used for voice and video
– Compressed RTP compresses the RTP, UDP,
and IP header from 40 bytes to 2 to 4 bytes
A Few Technologies for Meeting QoS
Requirements
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IETF controlled load service
IETF guaranteed service
IP precedence
IP differentiated services
IP Type of Service Field
• The type of service field in the IP header is
divided into two subfields
– The 3-bit precedence subfield supports eight
levels of priority
– The 4-bit type of service subfield supports four
types of service
• Although IP precedence is still used, the
type of service subfield was hardly ever
used
IP Type of Service Field
Type of Service Subfield
Bit 0
3
Precedence
0
D
4
T
8
5
6
R
C
7
0
15
D = Delay
T = Throughput
R = Reliability
C = Cost
24
31
Bit
Version
Header
Length
Identification
Time to Live
Total Length
Type of Service
Flags
Protocol
Fragment Offset
Header
Checksum
Source IP Address
Destination IP Address
Options
Padding
IP Differentiated Services (DS) Field
• RFC 2474 redefines the type of service field
as the Differentiated Services (DS) field
– Bits 0 through 5 are the Differentiated Services
Codepoint (DSCP) subfield
• Has essentially the same goal as the
precedence subfield
• Influences queuing and packet dropping
decisions for IP packets at a router output
interface
– Bits 6 and 7 are the Explicit Congestion
Notification (ECN) subfield
IP Differentiated Services (DS) Field
0
6
Differentiated Services Codepoint
Explicit Congestion Notification
0
8
Version
Header
Length
15
Differentiated Services
24
Total Length
31
Resource Reservation Protocol (RSVP)
• RSVP complements the IP type-of-service,
precedence, DSCP, and traffic-class
capabilities inherent in an IP header.
• RSVP supports mechanisms for hosts to
specify QoS requirements for individual traffic
flow.
• RSVP can be deployed on LANs and
enterprise WANs to support multimedia
applications or other types of applications with
strict QoS requirements.
Resource Reservation Protocol (RSVP)
• IP header type-of-service capabilities and
RSVP are examples of QoS signaling
protocols.
• In-band signaling means that bits within the
frame header signal to routers how the frame
should be handled.
• Out-of-band signaling means that hosts send
additional frames, beyond data frames, to
indicate that a certain QoS is desired for a
particular traffic flow.
Classifying LAN Traffic
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IEEE 802.1p
Classifies traffic at the data-link layer
Supports eight classes of service
A switch can have a separate queue for each
class and service the highest-priority queues
first
Cisco Switching Techniques
• Process switching is the slowest switching
method
• Fast switching allows highest throughput by
switching a packet using an entry in the fast-cache
that was created when a previous packet to the
same destination was processed.
• NetFlow switching is optimized for environments
where services must be applied to packets to
implement security, QoS features, and traffic
accounting. Example Internet and enterprise
network environment boundary.
Cisco Switching Techniques
• Cisco Express Forwarding (CEF) is a
technique for switching packets quickly across
large backbone networks and the Internet.
• CEF depended on a forwarding information
base (FIB), rather than caching techniques.
• FIB allows CEF to use less CPU resources
compared to other Layer 3 switching methods.
FIB contains forwarding information for all
routes in the routing tables.
Cisco Switching Techniques
Why did CEF evolve?
With the introduction of web-based
applications and other interactive applications
that are characterized by sessions of short
duration to multiple addresses.
It became very apparent that the cachebased system could not deliver the needed
performance for these applications.
Cisco Queuing Services
First in, first out (FIFO) queuing store packets
when the network is congested and forward the
packets in the order they arrived in when there is no
congestion. Disadvantage: No packet priority
scheme.
Priority queuing ensures that important traffic is
processed first. Priority is based on the type of protocol,
incoming interface, packet size, and source or
destination address. The priorities are high, medium,
normal, and low.
Cisco Queuing Services
Custom queuing is designed to allow the
network to be shared among applications with
different minimum bandwidth or latency
requirements. Custom queuing provides different
amounts of queue space to different protocols
and handles the queues in round-robin manner. A
particular protocol can be prioritized by
assigning it more queue space.
Custom queuing can be used to guarantee
bandwidth at a potential congestion point.
Cisco Queuing Services
Custom queuing helps ensure that each traffic
type receives a fixed portion of available bandwidth
and that when the link is under stress, no application
receives more than a predetermined proportion of
capacity.
Weighted fair queuing (WFQ) operates from
algorithms designed to reduce delay variability and
provide predictable throughput and response time
for traffic flows. Applications with small payloads
are not starved of bandwidth by applications that
send large packets.
Cisco Queuing Services
Class-based Weighted Fair Queuing
(CBWFQ) combines the best scenarios of priority,
custom, and weight-fair queuing.
Class-based WFQ allows you to define traffic
classes based on matching criteria such as protocol,
access control lists, and input interfaces.
Low latency queuing (LLQ) combines priority
queuing with CBWFQ. LLQ brings strict priority
queuing to CBWFQ. Strict priority queuing allows
delay-sensitive data such as voice to be sent before
packets in other queues are sent.
Priority Queuing
START
Packet in high
queue?
YES
NO
Packet in medium
queue?
YES
NO
Packet in normal
queue?
YES
NO
Packet in low
queue?
YES
Dispatch Packet
Continue
NO
Custom Queuing
START
(with Queue 1)
NO
Packet in
Queue?
YES
Next Queue
YES
Reached
transmission
window size?
NO
Dispatch Packet
Low-Latency Queuing
• One queue always gets the green light
– Use this for voice
• Combine this with class-based weighted
fair queuing
– Define traffic classes based on protocols,
access control lists, and input interfaces
– Assign characteristics to classes such as
bandwidth required and the maximum
number of packets that can be queued for
the class
Random Early Detection (RED)
• Congestion avoidance rather than congestion
management
• Monitors traffic loads and randomly discards
packets if congestion increases
• Source nodes detect dropped packets and slow
down
– Works best with TCP
• Weighted Random Early Detection
• Cisco’s implementation uses IP precedence or the DS
field instead of just randomly dropping packets
Traffic Shaping
• Manage and control network traffic to avoid
bottlenecks
• Avoid overwhelming a downstream router
or link
• Reduce outbound traffic for a flow to a
configured bit rate
– Queue bursts of traffic for that flow
Committed Access Rate (CAR)
• Cisco feature for classifying and policing
traffic on an incoming interface
• Supports policies regarding how traffic that
exceeds a certain bandwidth allocation should
be handled
• Can drop a packet or change the IP precedence
or DSCP bits
Security Penetration
A penetration test is a proactive and authorized
attempt to evaluate the security of an IT infrastructure
by safely attempting to exploit system vulnerabilities,
including OS, service and application flaws, improper
configurations, and even risky end-user behavior. Such
assessments are also useful in validating the efficacy of
defensive mechanisms, as well as end-users’ adherence
to security policies.
Security Penetration
Penetration tests are typically performed using
manual or automated technologies to systematically
compromise servers, endpoints, web applications,
wireless networks, network devices, mobile devices and
other potential points of exposure. Once vulnerabilities
have been successfully exploited on a particular system,
testers may attempt to use the compromised system to
launch subsequent exploits at other internal resources,
specifically by trying to incrementally achieve higher
levels of security clearance and deeper access to
electronic assets and information via privilege
escalation.
Summary
• An untested network design probably won’t
work.
• It’s often not practical to test the entire design.
• However, by using industry testing services
and tools, as well as your own testing scripts,
you can (and should) test the complex, risky,
and key components of a network design.
Summary
• Optimization provides the high bandwidth, low
delay, and controlled jitter required by many
critical business applications
• To minimize bandwidth utilization by multimedia
applications, use IP multicast
• To reduce serialization delay, use link
fragmentation and compressed RTP
• To support QoS and optimize performance, use IP
precedence, DSCP, 802.1p. advanced switching
and queuing methods, RED, CAR, etc.
Review Questions
• Why is it important to test your network
design?
• Why is regression testing important?
• What are some characteristics of well-written
acceptance criteria?
• What are some characteristics of a good
network simulation tool?
Review Questions
• Why is it important to optimize your
network?
• What has become of the IP type of service
field?
• What are some methods for marking
packets to identify the need for priority
handling?
• Compare and contrast Cisco queuing
services.
This Week’s Outcomes
– Industry Tests
– Build and Test a Prototype
– Write and Implement a Test Plan
– Tools for Testing a Network Design
– Multicasting
– QoS
– Queuing and Traffic Shaping
Due this week
• 12-1 – Concept questions 9
• 1-5-3 – Network design project
– New office network
Next week
• Review chapters 12 and 13 in Top-Down
Network Design
• 13-1 – Concept questions 10
• 4-2-3 – Networking practical experiences
– Basic network troubleshooting
Q&A
• Questions, comments, concerns?