1. Which of the following describes the functions of OSI Layer 3 protocols? Answer: A and C
2. Imagine that PC1 needs to send some data to PC2, and PC1 and PC2 are separated by several routers. What are the largest entities that make it from PC1 to PC2?
Answer: C and E
3. Which of the following does a router normally use when making a decision about routing TCP/IP?
4. Imagine a network with two routers that are connected with a point-to-point HDLC serial link. Each router has an Ethernet, with PC1 sharing the Ethernet with Router1, and PC2 sharing an Ethernet with Router2. When PC1 sends data to PC2, which of the following is true?
5. Which of the following are valid Class C IP addresses? Answer: B
6. What is the range for the values of the first octet for Class A IP networks? Answer: D
7. PC1 and PC2 are on two different Ethernets that are separated by an IP router. PC1's IP address is 10.1.1.1, and no subnetting is used. Which of the following addresses could be used for PC2?
Answer: D and F
8. How many valid host IP addresses does each Class B network contain? Answer: D
9. How many valid host IP addresses does each Class C network contain? Answer: G
10. Which of the following protocols allows a client PC to discover the IP address of another computer, based on that other computer's name?
Which of the following protocols allow a client PC to request assignment of an IP address as well as learn its default gateway?
Which term is defined by the following phrase: "the type of protocol that is being forwarded when routers perform routing."
What are the two main functions of each OSI Layer 3-equivalent protocol? Answer: Path selection, which is also called routing, and logical addressing.
Assume that PC1 sends data to PC2, and PC2 is separated from PC1 by at least one router. Are the IP addresses of the PCs in the same IP subnet? Explain your answer.
Answer: They must be in different subnets. IP addressing rules require that IP hosts separated by a router be in different subnets.
Assume that PC1 sends data to PC2, and PC2 is not separated from PC1 by at least one router. Are the IP, addresses of the PCs in the same IP subnet? Explain your answer.
Answer: They must be in the same subnet. IP addressing rules require that IP hosts not separated by a router be in the same subnet.
How many bits are present in an IP address?
Answer: IP addresses have 32 bits: a variable number in the network portion, and the rest of the 32 in the host portion. IP Version 6 uses a 128-bit address!
How many bits are present in an IPX address?
Answer: IPX addresses have 80 bits: 32 bits in the network portion and 48 bits in the node portion.
How many bits are present in an AppleTalk address?
Answer: AppleTalk addresses have 24 bits: 16 in the cable-range portion and 8 bits in the node portion.
7. Name the two main parts of an IPX address. Which part identifies which group this address is a member of?
Answer: Network number and node number are the two main parts of an IPX address. Addresses with the same network number are in the same group. On LAN interfaces, the node number is made to have the same value as the LAN MAC address.
8. Name the two main parts of an IP address. Which part identifies which group this address is a member of?
Answer: Network and host are the two main parts of an IP address. As described in Chapter 5, technically there are three portions of the IP address: network, subnet, and host. However, because most people think of the network and subnet portions as one portion, another correct answer to this question, using popular terminology, would be subnet and host. In short, without subnetting, the network part identifies the group; with subnetting, the network and subnet part together identifies the group.
9. PC1 sends data to PC2 using TCP/IP. Three routers separate PC1 and PC2. Explain why the statement "PC1 sends an Ethernet frame to PC2" is true or false.
Answer: False. Packets are delivered from end to end across a network, whereas frames simply pass between devices on each common physical network. The intervening routers discard the original Ethernet header, replacing it with other data-link headers as needed. A truer statement would be "PC1 sends an IP packet to PC2."
10. In IP addressing, how many octets are in 1 byte?
Answer: One. Octet is a generic word to describe a single byte. Each IP address is 4 bytes, or four octets, long.
11. Describe the differences between a routed protocol and a routing protocol.
Answer: The routed protocol defines the addressing and Layer 3 header in the packet that actually is forwarded by a router. The routing protocol defines the process of routers exchanging topology data so that the routers know how to forward the data. A router uses the routing table created by the routing protocol when choosing where to route a packet.
12. Name at least three routed protocols.
Answer: TCP/IP (IP), Novell (IPX), OSI (CLNP), DECnet (CLNP), AppleTalk (DDP), and VINES are some examples of routed protocols.
13. Name at least three IP routing protocols.
Answer: IP RIP, IP IGRP, IP/IPX/AppleTalk EIGRP, IP OSPF, OSI NLSP, and OSI IS-IS are some examples of routing protocols.
14. Imagine an IP host on an Ethernet, with a single router attached to the same segment. In which cases does an IP host choose to send a packet to this router instead of directly to the destination host, and how does this IP host know about that single router?
Answer: Typically an IP host knows to what router to send a packet based on its configured default router. If the destination of the packet is in another subnet, the host sends the packet to the default router. Otherwise, the host sends the packet directly to the destination host because it is in the same subnet and, by definition, must be on the same data link.
15. Name three items in an entry in any routing table.
Answer: A number that identifies a group of addresses, the interface out which to forward the packet, and the Layer 3 address of the next router to send this packet to are three items that you will always find in a routing table entry. For instance, IP routes contain subnet numbers, the outgoing interface, and the IP address of the next-hop router.
16. Name the parts of an IP address when subnetting is used.
Answer: Network, subnet, and host are the three parts of an IP address. However, many people commonly treat the network and subnet parts of an address as a single part, leaving only two parts, the subnet and host parts. On the exam, the multiple-choice format should provide extra clues as to which terminology is used.
17. How many valid IP addresses exist in a Class A network? (You may refer to the formula if you do not know the exact number.)
Answer: 16,777,214, derived by the formula 224 - 2.
18. How many valid IP addresses exist in a Class B network? (You may refer to the formula if you do not know the exact number.)
Answer: 65,534, derived by the formula 216 - 2.
19. How many valid IP addresses exist in a Class C network? (You may refer to the formula if you do not know the exact number.)
Answer: 254, derived by the formula 28 - 2.
20. What values can a Class A network have in the first octet? Answer: 1 through 126, inclusive.
21. What values can a Class B network have in the first octet? Answer: 128 through 191, inclusive.
22. What values can a Class C network have in the first octet? Answer: 192 through 223, inclusive.
23. When subnetting a Class B network, do you create the subnet field by taking bits from the network part of the address or the host part?
Answer: Host part.
24. When subnetting a Class B network, using the entire third octet for the subnet part, describe the number of possible subnets created.
Answer: The subnet part consists of a full octet, which is 8 bits long. You can number 28 things with 8 bits, or 256. However, 2 subnet numbers are reserved, leaving 254 subnets.
25. When subnetting a Class A network using the entire second octet for the subnet part, describe the number of hosts in each subnet.
Answer: The host part consists of two entire octets in this case, which is 16 bits long. You can number 2 things with 16 bits, or 65,536. However, 2 subnet numbers are reserved, leaving 65,534 hosts per subnet.
26. When a router hears about multiple routes to the same subnet, how does it choose which route to use?
Answer: Routing protocols use a metric to describe how good each route is. The lower the metric is, the better the route is.
27. What is the primary purpose of a routing protocol?
Answer: Routing protocols discover the routes in network and build routing tables.
28. True or false: "Routing protocols are required to learn routes of directly connected subnets."
Answer: False. Routers add routes to directly connected subnets when the interfaces initialize. No routing protocols are needed.
29. Which IP routing protocols are Cisco proprietary? Answer: IGRP and EIGRP.
30. List the similarities and differences between RARP and BOOTP.
Answer: Both protocols send broadcasts looking for a server, and they hope to have the server assign them an IP address. BOOTP also can be used to assign other parameters, such as the subnet mask, default gateway, DNS address, and filenames for downloading an operating system.
31. List the similarities and differences between DHCP and BOOTP.
Answer: Both protocols send broadcasts looking for a server, and they hope to have the server assign them an IP address. Both can be used to assign a large variety of parameters, such as the subnet mask, default gateway, DNS address, and filenames for downloading an operating system. DHCP does not require that the server be preconfigured with the MAC addresses of all the DHCP client PCs, making it much more scalable.
32. List the similarities and differences between ARP and DNS.
Answer: Both protocols send messages with one bit of information, hoping to learn another bit of information. The similarities do not go beyond that fact. DNS requests are unicast IP packets sent specifically to the DNS server, whereas ARP uses a LAN broadcast frame. DNS queries supply a name, expecting to hear the corresponding IP address back from the server. ARP requests supply an IP address, hoping to hear a corresponding MAC address not from a server, but from the host that uses that IP address.
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