Foundation Summary

The "Foundation Summary" section of each chapter lists the most important facts from the chapter. Although this section does not list every fact from the chapter that will be on the CCDA exam, a well-prepared CCDA candidate should at a minimum know all the details in each "Foundation Summary" before taking the exam.

This chapter covered the following topics that you will need to master for the CCDA exam:

■ IPv4 header—Know each field of the IPv4 header.

■ IPv4 addressing—Know IPv4 address classes, private addressing, and NAT.

■ IPv4 address subnets—Know VLSMs with a design example.

■ Address assignment and resolution—Know dynamic IP assignment and address-resolution protocols such as BOOTP, DHCP, DNS, and ARP.

Table 7-23 outlines the IPv4 address classes.

Table 7-23 IPv4 Address Classes

Address Class

High-Order Bits

Network Numbers

A

Oxxxxxxx

1.0.0.0 to 126.0.0.0

B

lOxxxxxx

128.0.0.0 to 191.255.0.0

C

110xxxxx

192.0.0.0 to 223.255.255.0

D

1110xxxx

224.0.0.0 to 239.255.255.255

E

1111xxxx

240.0.0.0 to 254.255.255.255

Table 7-24 summarizes the IPv4 private address space. Table 7-24 IPv4 Private Address Space

Class Type

Start Address

End Address

Class A

10.0.0.0

10.255.255.255

Class B

172.16.0.0

172.31.255.255

Class C

192.168.0.0

192.168.255.255

Table 7-25 shows subnet mask representations.

Table 7-25 Subnet Mask Representations

Dotted Decimal

Prefix

Hexadecimal

255.0.0.0

/8

FF000000

255.128.0.0

/9

FFA00000

255.192.0.0

/10

FFC00000

255.224.0.0

/11

FFE00000

255.240.0.0

/12

FFF00000

255.248.0.0

/13

FFFA0000

255.252.0.0

/14

FFFC0000

255.254.0.0

/15

FFFE0000

255.255.0.0

/16

FFFF0000

255.255.128.0

/17

FFFFA000

255.255.192.0

/18

FFFFC000

255.255.224.0

/19

FFFFE000

255.255.240.0

/20

FFFFF000

255.255.248.0

/21

FFFFFA00

255.255.252.0

/22

FFFFFC00

255.255.254.0

/23

FFFFFE00

255.255.255.0

/24

FFFFFF00

255.255.128.0

/25

FFFFFFA0

255.255.192.0

/26

FFFFFFC0

255.255.255.224

/27

FFFFFFE0

255.255.255.240

/28

FFFFFFF0

255.255.255.248

/29

FFFFFFF8

255.255.255.252

/30

FFFFFFFC

255.255.255.254

/31

FFFFFFFE

255.255.255.255

/32

FFFFFFFF

The following list reviews the various IPv4 address types:

■ Unicast—The IP address of an interface on a single host. It can be a source or destination address.

■ Multicast—An IP address that reaches a group of hosts. It is only a destination address.

■ Broadcast—An IP logical address that reaches all hosts in an IP subnet. It is only a destination address.

Table 7-26 summarizes the fields of the IP header.

Table 7-26 IPv4 Header Fields

Field

Length

Description

Version

4 bits

Indicates the IP header's format, based on the version number. Set to 0100 for IPv4.

IHL

4 bits

Length of the header in 32-bit words.

ToS

8 bits

QoS parameters.

Total length

16 bits

Length of the packet in bytes, including header and data.

Identification

16 bits

Identifies a fragment.

Flags

3 bits

Indicates whether a packet is fragmented and whether more fragments follow.

Fragment offset

13 bits

Location of the fragment in the total packet.

Time to live

8 bits

Decremented by 1 by each router. When this is 0, the router discards the packet.

Protocol

8 bits

Indicates the upper-layer protocol.

Header checksum

16 bits

Checksum of the IP header; does not include the data portion.

Source address

32 bits

IP address of the sending host.

Destination address

32 bits

IP address of the destination host.

IP options

Variable

Options for security, loose source routing, record route, and timestamp.

Padding

Variable

Added to ensure that the header ends in a 32-bit boundary.

Table 7-27 compares DSCP and IP precedence values used to assign priority and apply policies to IP packets.

Table 7-27 DSCP and IP Precedence Values

IP Precedence

DSCP

Service Type

Decimal

Binary

Class

Decimal

Binary

Routine

0

000

Best effort

0

000 to 000

Priority

Forwarding (AF) Class l

8

001 to 000

Immediate

2

010

AF Class 2

16

010 to 000

Flash

3

011

AF Class 3

24

011 to 000

Flash override

4

100

AF Class 4

32

100 to 000

Critical

Forwarding (EF)

40

101 to 000

Internetwork control

6

110

Control

48

110 to 000

Network control

7

111

Control

56

As mentioned in the Introduction, you have two choices for review questions: here in the book or the exam questions on the CD-ROM. The answers to these questions appear in Appendix A.

For more practice with exam format questions, use the exam engine on the CD-ROM.

1. List the RFC 1918 private address space.

2. What is the difference between VLSM and CIDR?

3. Fill in the blank:_maps FQDN to IP addresses.

4. True or false: You can use DHCP to specify the TFTP host's IP address to a client PC.

5. True or false: 255.255.255.248 and /28 are two representations of the same IP mask.

6. True or false: Upper-layer protocols are identified in the IP header's protocol field. TCP is protocol 6, and UDP is protocol 17.

7. Fill in the blank: Without any options, the IP header is_bytes in length.

8. The IP header's ToS field is redefined as the DS field. How many bits does DSCP use for packet classification, and how many levels of classification are possible?

9. True or false: NAT uses different IP addresses for translations. PAT uses different port numbers to identify translations.

10. True or false: The IP header's header checksum field performs the checksum of the IP header and data.

11. Calculate the subnet, the address range within the subnet, and the subnet broadcast of the address 172.56.5.245/22.

12. When packets are fragmented at the network layer, where are the fragments reassembled?

13. Which protocol can you use to configure a default gateway?

b. DHCP

d. RARP

14. How many host addresses are available with a Class B network with the default mask?

15. Which of the following is a dotted-decimal representation of a /26 prefix mask?

a. 255.255.255.128

b. 255.255.255.192

c. 255.255.255.224

d. 255.255.255.252

16. Which network and mask summarize both the 192.170.20.16/30 and 192.170.20.20/30 networks?

17. Which AF class is backward-compatible with IP precedence bits' flash traffic?

18. Which of the following is true about fragmentation?

a. Routers between source and destination hosts can fragment IPv4 packets.

b. Only the first router in the network can fragment IPv4 packets.

c. IPv4 packets cannot be fragmented.

d. IPv4 packets are fragmented and reassembled at each link through the network.

19. A packet sent to a multicast address reaches what destination(s)?

a. The nearest destination in a set of hosts.

b. All destinations in a set of hosts.

c. Broadcasts to all hosts.

d. Reserved global destinations.

20. What are three types of IPv4 addresses? Answer the following questions based on the given scenario and figure.

Company VWX has the network shown in Figure 7-8. The main site has three LANs with 100, 29, and 60 hosts. The remote site has two LANs, each with 100 hosts. The network uses private addresses. The Internet service provider assigned the company the network 210.200.200.8/26.

Figure 7-8 Scenario Diagram

Figure 7-8 Scenario Diagram

21. The remote site uses the network prefix 192.168.10.0/24. What subnets and masks can you use for the LANs at the remote site and conserve address space?

a. 192.168.10.64/26 and 192.168.10.192/26

b. 192.168.10.0/25 and 192.168.10.128/25

c. 192.168.10.32/28 and 192.168.10.64/28

d. 192.168.10.0/30 and 192.168.10.128/30

22. The main site uses the network prefix 192.168.15.0/24. What subnets and masks can you use to provide sufficient addresses for LANs at the main site and conserve address space?

a. 192.168.15.0/25 for LAN 1, 192.168.15.128/26 for LAN 2, and 172.15.192.0/27 for LAN 3

b. 192.168.15.0/27 for LAN 1, 192.168.15.128/26 for LAN 2, and 172.15.192.0/25 for LAN 3

c. 192.168.15.0/100 for LAN 1, 192.168.15.128/60 for LAN 2, and 172.15.192.0/29 for LAN 3

d. 192.168.15.0/26 for LAN 1, 192.168.15.128/26 for LAN 2, and 172.15.192.0/29 for LAN 3

23. Which network and mask would you use for the WAN link to save the most address space?

a. 192.168.11.240/27

b. 192.168.11.240/28

c. 192.168.11.240/29

d. 192.168.11.240/30

24. What networks does Router C announce to the Internet service provider's Internet router?

c. 192.168.10.0/25 summary address d. 201.200.200.8/29 and 192.168.10.0/25

25. What technology does Router C use to convert private addresses to public addresses?

d. VLSM

26. What mechanism supports the ability to divide a given subnet into smaller subnets based on need?

d. VLSM

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