Chapter 8 - TCP / IP Internetworking I
6b. Express this mask in prefix notation.
Answer: /8
20f. How many bits are there in a field?
Answer: 16 bits
4a. Connecting different networks is the main job of what type of router?
Answer: Border Router
22e. Does the Payload Length Field include the lengths of any extension headers in the packet?
Answer: Yes, It includes both extension headers and the data field.
12c. Why is decision caching dangerous?
Answer: a cached decision that is used for too long will result in non-optimal routing;
20g. How are fields separated?
Answer: fields are separated by colons
20d. Are simplified IPv6 addresses written with decimal or hexadecimal symbols?
Answer: hexadecimal
20c. Are simplified IPv6 addresses written in uppercase or lowercase letters?
Answer: lowercase
3a. What are the three parts of an IPv4 address?
Answer: the 3 parts re: (1) Network, (2) Subnet, & (3) Host Parts
5b. What do the 1s in an IPv4 network mask correspond to in IPv4 addresses?
Answer: the Network part
23d. How does the last extension header before a UDP datagram indicate that the UDP datagram comes next?
Answer: with the value 6 in the extension header
15a. Distinguish between application message fragmentation and packet fragmentation.
Answer: (1) application message fragmentation is when application messages are fragmented into individual packets (2) packet fragmentation is when routers further fragment individual packets
20h. How many fields are there in an IPv6 address?
Answer: 16 fields ( 16 x 4 = 128 bits )
6a. A mask has eight 1s, followed by 0s. Express this mask in dotted decimal notation.
Answer: 255.0.0.0
6c. In prefix notation, a mask is /16. Express this mask in dotted decimal notation.
Answer: 255.255.0.0
6d. Express the mask /18 in dotted decimal notation. (You will need a calculator for this.)
Answer: 255.255.48.0
5a. How many bits are there in an IPv4 mask?
Answer: 32 bits
3c. What is the total length of an IPv4 address?
Answer: 32 bits long
9c. Why is the last row called the default row?
Answer: A "default" is something you get if you do not have a more specific choice. Having a value of 0.0.0.0, this row ensures that at least one row will match the destination IPv4 address of every arriving packet.
25b. Distinguish between four-way closes and abrupt resets.
Answer: A four-way close consists of a normal TCP close of two FIN segments, one in each direction, plus their acknowledgements; an abrupt close is a one-way communication where either side sends a TCP reset segment (RST) to end the communication. There is no acknowledgement.
16b. What does the next router do?
Answer: A router decrementing the TTL field to zero with discard the packet.
25d. What other type of segment is not acknowledged?
Answer: A segment that is nothing more than a pure acknowledgement is not acknowledged because doing so would create an endless loop of acknowledgements.
12b. How would decision caching speed the routing decision for packets after the first one?
Answer: Because it will not have to make the 3-step destination decision every time, it will use the cached decision.
23a. Why is handling options the way that IPv4 does undesirable?
Answer: Because many options are only relevant to the destination host. yet each router must check each packet for options anyway, adding cost and time
25c. Why is a reset segment not acknowledged?
Answer: Because the RST's sender is no longer listening. (ie: someone abruptly hanging up the telephone.)
20b. Why must simplification rules be followed precisely?
Answer: Because when everyone writes them in the same way, it easy to test whether two addresses are the same
22a. How do the Version Number Fields in IPv4 and IPv6 differ?
Answer: Both headers begin with a 4-bit Version Number Field. For IPv4, the field value is 0100 (four). For IPv6, it is 0110 (six).
5c. What do the 1s in an IPv4 subset mask correspond to in IPv4 addresses? Think carefully!
Answer: Both the Network and the Subnet Parts
22h. What is the consequence IPv6 not having a header checksum field?
Answer: Dropping the checksum field slashes packet handling time on routers.
14c. How can the ECN Field be used?
Answer: ECN (Explicit Congestion Notification) field can be used to reduce the transmission frequency between a pair of hosts to cope with congestion between them
23b. Why is the approach of using optional extension headers desirable?
Answer: Each extension header has a well-defined purpose making it more efficent
16a. What does a router do if it receives a packet with a TTL value of 2?
Answer: Each router will decrease the TTL (Time to Live) Field by 1 as it is going through the routing process.
25a. What is a FIN segment?
Answer: FIN is the normal protocol of closing a connection. It consists of two FIN segments, one in each direction, plus their acknowledgments.
22c. What is the Purpose Of the Flow Label Field?
Answer: Flow Label Field value indicates that the packet is a member of a particular flow. The router has rules that apply to every packet in the flow.
20e. How many symbols are there in a field?
Answer: Four - Hex symbols are grouped in tetrad (groups of four) fields
22f. How is the Hop Limit Field used?
Answer: Hop Limit Field is like the IPv4 time to live field. Each router along the way decrements this field's value by one, and if a router decrements it to zero, the router discards the packet.
23e. If you see 0 in the Next Header Field of a header, what will follow this header?
Answer: Hop-by-Hop options
19. What has been holding back the adoption of IPv6?
Answer: Implementation is a long, expensive, and complex process requiring employees who understand this new protocol.
7. Why are routing tables more complex than Ethernet switching tables? Give a detailed answer.
Answer: In Ethernet switching, there is only a single path between any two hosts across the network; contrast, routers are organized in meshes allowing many possible alternative routes between endpoints.
8a. In a routing table, what does a row represent?
Answer: In a routing table, each row represents a route
4b. What type of router connects different subnets?
Answer: Internal Router
14a. What is the main version of the Internet Protocol in use today?
Answer: Internet Protocol Version 4 (IPv4)
8d. What is the advantage of the answer to the previous subparts of this question?
Answer: It means that a router needs many fewer rows than an Ethernet switch would need for the same number of addresses.
17. What problem is caused by the way that IPv4 handles options?
Answer: It slows things down because the lack of required order with the options means that each router must look at every option to see if it applies.
16d. What will the destination internet process do if it see 17 in the Data Field?
Answer: It will recognize the contents Data field as UDP
1a. Which two layers standardize Ethernet and Wi-Fi operation?
Answer: Layers 1 and 2
1b. Which two layers standardize most of the Internet's operation?
Answer: Layers 3 and 4
15d. Does IPv6 allow packet fragmentation?
Answer: NO
22g. Does IPv6 have a header checksum field?
Answer: NO
8c. Do routers have a row for each individual IPv4 address?
Answer: No, It only needs a row for each group of IPv4 addresses.
21f. Which RFC is used to write IPv6 addresses in canonical form?
Answer: RFC 5952
2a. What are interfaces?
Answer: Router Ports are called interfaces
11b. What are router ports called?
Answer: Router ports are called interfaces.
2b. Explain the network adage "Switch where you can; route where you must."
Answer: Routing is more complex and expensive than switching .
3d. In the IPv4 address, 10.11.13.13, what is the network part?
Answer: Since the lengths of each section vary, you cannot tell which bits correspond to the network or subnet parts.
11a. Distinguish between Step 2 and Step 3 in routing.
Answer: Step 2 is Selecting the Best-Match Row and Step 3 is Sending the Packet Back Out.
26a. Why can TCP handle long application messages?
Answer: TCP can handle application messages of almost any length. TCP does this by fragmenting long messages into many pieces and sending each segment in its own TCP segment.
24b. How many flag fields do TCP headers have?
Answer: TCP has nine single-bit fields.
3e. If you see an IPv4 address, what do you know for certain?
Answer: That is is 32 bits long.
22b. What is the general purpose of the Diffserv subfield?
Answer: The 6-bit Differentiated Services (Diffserv) subfield specifies whether this particular packet should be given routine best-effort service, high-priority low-latency service, or some other type of service.
14b. Which field can be used to specify quality of service?
Answer: The Differentiated Services Control Point field
1c. What do IP, TCP, and UDP govern?
Answer: The Internet
26c. What is the maximum application message size when UDP is used at the transport layer?
Answer: The Length Field in the UDP header is 16 bits long, so the maximum length of the UDP data field (and therefore the maximum length of an application message) is 65,536 octets.
22d. In IPv6, how can the receiver tell the length of packet?
Answer: The Payload Length Field gives the length of the packet payload, which is everything beyond the 40-octet main packet header. The Payload Length Field is 16 bits long.
16c. What does the Protocol Field value tell the destination host?
Answer: The Protocol Field value tells the receiver which process should receive these contents.
5d. When a network mask is applied to any IPv4 address on the network, what is the result?
Answer: The Subnet and Host parts become zeros
24c. If the ACK bit is set, what other field must have a value?
Answer: The acknowledgment field must be filled in to indicate which message is being acknowledged.
23f. Why are the terms payload and data field not synonymous?
Answer: The data field is the content message being delivered. The payload is everything that follows the main header. So the payload consists of both extension headers and the data field.
10b. If any row other than the default row matches an IPv4 address, why will the router never choose the default row?
Answer: The default row always has a prefix of 0/. This is the shortest possible length of match. If any other row matches, its length of match will be longer than the default.
23c. What is often the only extension header that routers must consider?
Answer: The main header's Next Header Field specifies the first extension header. This is often the only extension header that routers need to deal with.
9d. Why must a router look at all rows in a routing table?
Answer: The router must do this to ALL rows because there may by multiple matches.
12a. What should a router do if it receives several packets going to the same destination IPv4 address?
Answer: The router should go through the entire 3-step process for each packet.
1d. What do TCP/IP supervisory protocols govern?
Answer: They govern how routers and hosts on the internet work beyond the delivery of packets.
18b. How does IPv6 solve this problem?
Answer: They moved from a 32-bit address to a 128-bit address (creating a lot more addresses!)
18a. What is the main problem with IPv4 that IPv6 was created to solve?
Answer: They ran out of IPv4 addresses. Today there are no more to distribute.
20a. Why are IPv6 addresses simplified?
Answer: To make it easier for humans to read and wto make them searchable in text documents.
26b. Why can UDP not handle long application messages?
Answer: UDP, unlike TCP, cannot do segmentation. The entire application message must fit into a single UDP datagram.
3b. How long is each part?
Answer: Variable part lengths
8b. Do Ethernet switches have a row for each individual Ethernet address?
Answer: Yes