Chapter 3 Network Management

14. Priority Level

The 3-bit field used to give a frame one of eight priority levels from 000 (zero) to 111 (eight).

f) What kind of message can agents initiate?

Traps (alarms).

10. Jitter

Variability in latency.

e) What is jitter?

Variation in latency in arrival times among packets.

c) What is latency?

delay in transmission.

b) For the HDTV program in Figure 3-3, which of the speeds shown will allow real-time streaming?

10 Mbps and higher would be able to download the program fast enough for it to be received in real time.

f) If you have 10 site pairs connected by seven transmission links, how many rows of traffic data will you have in your traffic table?

10.

g) How many columns?

7.

19. managed devices

A device that can be managed remotely via the Simple Network Management Protocol

b) How long do momentary traffic peaks last?

A fraction of a second to a few seconds.

11. Service Level Agreement

A quality-of-service guarantee for throughput, availability, latency, error rate, and other matters.

23. Software Defined Networking

A radical change in networking that removes the control function from individual switches, routers, access points, and other devices.

15. Edge Router

A router at the edge of the network between an organization and its Internet service provider.

21. Management Information Base (MIB)

A specification that defines what objects can exist on each type of managed device and also the specific characteristics of each object; the actual database stored on a manager in SNMP.

17. Application Program Interfaces (APIs)

A standardized interface between programs.

13. Momentary Traffic Peaks

A surplus of traffic that briefly exceeds the network's capacity, happening only occasionally.

j) A business has an Internet access line with a maximum speed of 100 Mbps. What two things are wrong with this SLA?

An SLA should promise a minimum speed, and there should be a minimum allowable time at a lower speed.

16. Access Control List

An ordered list of pass/deny rules for a firewall or other device.

g) Is traffic shaping done before or after the traffic enters the network?

Before traffic enters the network.

a) Is transmission speed usually measured in bits per second or bytes per second?

Bits per second (bps).

j) What must be done if this is not possible or not sufficient?

Capacity must be increased.

a) Distinguish between dedicated and multiplexed transmission links.

Dedicated links are unshared. Multiplexing transmits the traffic of multiple conversations over a shared trunk link.

8. Latency

Delay, usually measured in milliseconds.

c) Distinguish between SNMP Get and SNMP Set commands.

Get commands ask for information. Set commands tell the agent to change the way its device operates.

f) Would an SLA guarantee specify a highest jitter or a lowest jitter?

Highest jitter.

e) Would an SLA specify highest latency or lowest latency?

Highest latency.

h) If carrier speed falls below its guaranteed speed in an SLA, under what circumstances will the carrier not have to pay a penalty to the customers?

If the length of failure time is less than allowed in the SLA.

26. Northbound APIs

In SDN, an application program interface between an SDN application and the SDN controller.

27. Southbound APIs

In SDN, an application program interface between an SDN controller and a switch, router, or other device.

b) Distinguish between individual and aggregate throughput.

In a shared system, the aggregate throughput is the throughput available to all users. Individual throughput is the speed an individual receives; it is lower than the aggregate throughput. The individual throughput is the aggregate throughput divided by the number of active users at the moment.

25. Error Rate

In biometrics, the normal rate of misidentification when the subject is cooperating.

d) Where does the SNMP manager store the information it receives from Get commands?

In the Management Information Base (MIB).

d) Where is it placed in SDN?

In the SDN controller.

c) Where was the control function placed traditionally?

In the individual switches and routers.

a) If you Ping a host and it does not respond, what can you conclude?

It is not reachable. Possibilities for this:It may not be functioning. There may be no network path to it. There may be a network failure A firewall may be blocking the ping. (This is common.)

g) What happens if a carrier does not meet its SLA guarantee?

It must pay a penalty unless the length of failure time is greater than allowed in the SLA.

e) Why can good security save money in network management?

It permits the company to use Set commands for doing remote diagnosis and management.

g) Why is network automation important?

It reduces management costs.

a) Why is the automation of network management tasks important?

It reduces management work and therefore costs.

c) What two problems do they create?

Latency. Also packet loss if the momentary peak is too long.

b) If 100 conversations averaging 50 Mbps are multiplexed on a transmission line, will the required transmission line capacity be less than 5 Gbps, equal to 5 Gbps, or more than 5 Gbps?

Less than 5 Gbps. (Individual conversations have bursts and silences; only traffic during the bursts is normally carried.

24. Traffic Shaping

Limiting access to a network based on type of traffic.

c) What is the business benefit of multiplexing?

Lower transmission cost.

d) Would an SLA specify a highest availability or a lowest availability?

Lowest availability.

c) Would an SLA specify a highest speed or a lowest speed?

Lowest speed.

a) List the main elements in SNMP.

Manager, managed devices, agents, MIB. Network visualization program is outside SNMP.

d) In what units is latency measured?

Milliseconds.

a) Distinguish between chronic lack of capacity and momentary traffic peaks.

Momentary traffic briefs are very brief. Their effects can be reduced by good management. Chronic lack of capacity means that traffic exceeds capacity most of the time. Their effects cannot be reduced by good management. The only thing to do is add sufficient capacity most of the time.

f) Why may adding applications that cannot tolerate latency and jitter be expensive?

More expensive switches and routers may be necessary. If so, purchase and installation costs may be high.

f) Comparing e-mail and VoIP, what priority would you give to network control messages sent to switches and routers? (The answer is not in the text.) Explain your reasoning.

Network control messages should get highest priority because they are crucial for network operation, and latency or loss can be very harmful to network performance.

b) Why are QoS metrics important?

Networks must not just work. They must work well. Without QoS metrics, companies could not assess how well they worked.

b) Does the SNMP manager communicate directly with the managed device? Explain.

No. It communicates with the network management agents, not the individual managed devices.

a) What are QoS metrics? (Do not just spell out the acronym.)

Numerical measures for quality of service variables.

1. Quality of Service (QoS)

Numerical service targets that must be met by networking staff.

i) If there is chronic lack of capacity, which of the mechanisms describe in these sections can help?

Only traffic shaping.

d) What three choices do you have for reducing the impact of delays on traffic?

Overprovisioning (adding more capacity than will be needed nearly all the time). Prioritizing latency-intolerant traffic. Giving QoS guarantees to certain types of traffic.

e) What is the advantage of each compared to the others?

Overprovisioning wastes capacity but adds no management costs. Priority adds no capacity costs but requires management costs. QoS guarantees are fine for guaranteed traffic but by reserving capacity, QoS makes things worse for other traffic.

c) What types of latency do Ping and Traceroute give you?

Ping gives round-trip latency to the pinged host. Traceroute also gives round-trip latency to each router along the route, as well as to the pinged host.

e) Distinguish between Ping and Traceroute.

Ping only pings a host. Traceroute also pings all routers along the route.

d) In a coffee shop, there are 10 people sharing an access point with a rated speed of 2 Gbps. The throughput is half the rated speed. Several people are downloading. Each is getting an average of 100 Mbps. How many people are using the Internet at that moment?

Rated speed: 2 Gbps Throughput: 1 Gbps (half of the rated speed) Individual throughput: 100 Mbps Simultaneous users: 10

a) What are the benefits of Software-Defined Networking?

Reducing configuration costs. Speeding configuration changes.

h) What two choices does traffic shaping present for forbidden or undesirable traffic submitted to the network?

Refuse all access. Limit access to a certain percentage of capacity.

i) Does residential ISP service usually offer SLA guarantees? Why or why not?

Residential service rarely offers SLAs because the service would be too expensive.

f) In Figure 3-21, what jump causes the second most latency?

Router 18 (50 ms).

e) What do northbound APIs connect?

SDN applications to the SDN controller.

b) What two things does Ping tell you about a host that replies?

That it is reachable and the round-trip latency to reach it.

a) What are service level agreements?

Service level agreements (SLAs) are contracts that guarantee minimum levels of performance for various QoS metrics such as speed and availability.

g) Which type of API must router and switch designers support?

Southbound APIs.

f) What do southbound APIs connect?

The SDN controller to individual devices.

7. Availability

The ability of a network to serve its users.

6. Individual Throughput

The actual speed a single user receives (usually much lower than aggregate throughput in a system with shared transmission speed).

b) Distinguish between the control function and the forwarding function.

The control function configures the device's forwarding rules. The forwarding function forwards frames and packets according to the forwarding rules.

3. Rated Speed

The official standard speed of a technology.

2. Bits Per Second (bps)

The measure of network transmission speed.

h) What is the relationship between the network visualization program and the SNMP manager?

The network visualization program draws its data from the manager and the MIB and sends commands to the manager.

a) What is availability?

The percentage of time a resource is available for use.

20. Simple Network Management Protocol (SNMP)

The protocol that allows a general way to collect rich data from various managed devices in a network.

a) Distinguish between rated speed and throughput.

The rated speed is the speed the standard or the carrier specifies. Throughput is the speed you actually receive.

18. Round-Trip Latency

The time delay between when a message is sent and the response is received.

4. Throughput

The transmission speed that users actually get. Usually lower than a transmission system's rated speed.

9. Milliseconds (ms)

The unit of time in which latency is measured.

b) Does an SLA measure the best case or the worst case?

The worst case. If you are guaranteed an eight-ounce steak, it means that you will not get less. If it was the best case, you would get no more than 8 ounces, which would actually be nice.

a) What do network visibility tools allow a manager to do?

They allow management to understand what is happening throughout a network.

b) Why are standard configurations desirable?

They save configuration time and reduce configuration errors. Their configuration can then be modified as needed for that particular router's role.

b) Do they cost more money than they save? Explain.

They save more money than they cost.

12. Traffic Analysis

This is a method of uncovering information by watching traffic patterns on a network.

c) You are working at an access point with 20 other people. Three are doing a download at the same time you are. The rest are looking at their screens or sipping coffee. The access point you share has a rated speed of 150 Mbps and provides a throughput of 100 Mbps. How much speed can you expect on average for a download?

Throughput = 100 Mbps

5. Aggregate Throughput

Throughput shared by multiple users; individual users will get a fraction of this throughput.

h) Why are applications necessary for SDN to be successful?

To reduce the work of the network administrators as much as possible.

d) If a router causes problems, how can you diagnose this with Ping?

You can ping all hosts, then look at a map of which fail to respond. You may see that they are all behind a router. That router may be down.

b) When should you measure error rates? Why?

You should measure error rates when traffic is high because this is when errors are highest.

22. Network Visualization Program

takes results from the MIB (management information base) and interprets the data to display results in maps, find root causes for problems, and do other tasks