1. ITEC 275 Computer Networks – Switching, Routing, and WANs
Week 11
Robert D’Andrea
Some slides provide by Priscilla Oppenheimer and used with permission

2. 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

3. 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 agreed-up service
Identify bottlenecks or connectivity problems
Determine optimization techniques that will be necessary
This is a short list of the reasons that testing a new network design is important. There are many other reasons also, many of which are listed in Top-Down Network Design, the book.

4. 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
Convincing mangers and coworkers 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
This is a short list of the reasons that testing a new network design is important. There are many other reasons also, many of which are listed in Top-Down Network Design, the book.

5. Testing Your Network Design
Use industry testing services
Build and test a prototype system
Use third-party and Cisco tools

6. 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.

7. 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 that component testing. There will be a need for unit, integration, and system testing.

8. Scope of a Prototype System
It’s not generally practical to implement a full-scale 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.

9. 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 network during typical loads and benchmark the performance

10. 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 project

11. 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

12. 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 a baseline

13. Types of Tests 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)
Regression testing makes sure the new system doesn’t break any applications or components that were known to work and perform to a certain level before the new system was installed. Regression testing does not test new features or upgrades. Instead, it focuses on existing applications. Regression testing should be comprehensive, and is usually automated to facilitate comprehensiveness.

14. 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

15. Example Test Script Workstations Server 1 Firewall Network A Network B
Protocol Analyzer
Protocol Analyzer

16. 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.

17. Example Test Script (continued)
Start capturing network traffic on the protocol analyzer on Network A.
Start capturing network traffic on the protocol analyzer on Network B.
Run Application ABC on a workstation located on Network A and access Server 1 on Network B.
Stop capturing network traffic on the protocol analyzers.

18. 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.

19. Example Test Script (continued)
Display data on Network B’s protocol analyzer and verify that the analyzer did not capture any Application-ABC traffic from the workstation.
Log the results of the test in the project log file.
Save the protocol-analyzer trace files to the project trace-file 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.

20. 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. - See more at:

21. 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

22. 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.

23. 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.

24. Reasons to Optimize 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

25. IP Multicast

26. IP Multicast
Applications that take advantage of multicast include video conferencing, corporate communications, distance learning, and distribution of software, stock quotes, and news.

27. 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

28. IP Multicast Helps Optimize Bandwidth Usage
To support IP multicasting, the Internet authorities have reserved the multicast address range of E to E-7F-FF-FF for Ethernet and Fiber Distributed Data Interface (FDDI) media access control (MAC) addresses. 

29. IP Multicast Helps Optimize Bandwidth Usage
To map an IP multicast address to a MAC-layer 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. 

30. IP Multicast Addressing
Uses Class D multicast destination address to
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

31. 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

32. 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

33. 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 protocol-independent because PIM does not include its own topology discovery mechanism, but instead uses routing information supplied by other routing protocols.

34. 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.

35. 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.

36. PIM Dense Mode

37. PIM Dense Mode

38. 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 membership-report message, and detach from a group by sending a leave message.

39. 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 wide-area usage.

40. 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.

41. 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.

42. 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

43. A Few Technologies for Meeting QoS Requirements
IETF controlled load service
IETF guaranteed service
IP precedence
IP differentiated services

44. 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

45. IP Type of Service Field
Type of Service Subfield
Bit 3 4 5 6 7
D = Delay
T = Throughput
R = Reliability
C = Cost
Precedence D T R C 8 15 24 31
Bit
Version
Header Length
Type of Service
Total Length
Identification
Flags
Fragment Offset
Time to Live
Protocol
Header Checksum
Source IP Address
Destination IP Address
Options
Padding

46. 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

47. IP Differentiated Services (DS) Field6
Differentiated Services Codepoint
Explicit Congestion Notification 8 15 24 31
Header Length
Version
Differentiated Services
Total Length

48. 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.

49. 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.

50. Classifying LAN Traffic
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

51. 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.
These are technologies for “switching” (forwarding) packets through a router.

52. 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.
These are technologies for “switching” (forwarding) packets through a router.

53. 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 cache-based system could not deliver the needed performance for these applications.
These are technologies for “switching” (forwarding) packets through a router.

54. 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 type of protocol, incoming interface, packet size, and source or destination address. The priorities are high, medium, normal, and low.

55. 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.

56. 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.

57. Cisco Queuing Services
Class-based WFQ (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.

58. 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

59. Priority Queuing START NO Packet in high queue? NO
Packet in medium queue?
YES NO
Packet in normal queue?
YES NO
Packet in low queue?
YES
YES
Dispatch Packet
Continue

60. Reached transmission window size?
Custom Queuing
START (with Queue 1)
Packet in Queue? NO
YES
Reached transmission window size?
YES NO
Next Queue
Dispatch Packet

61. 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

62. 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

63. 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

64. 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

65. 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.

66. 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.

67. 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?

68. 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.

69. 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

70. Due this week 12-1 – Concept questions 9
1-5-3 – Network design project
New office network

71. 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

72. Q & A
Questions, comments, concerns?