Inside Back Cover
| Q | Why is header information enclosed at each layer of the TCP/IP protocol stack? |
| A | Because each protocol layer on the receiving machine needs different information to process the incoming data, each layer on the sending machine encloses a package of information inside a header. |
| Q | How large is the subnet ID field on a Class B network with the mask 255.255.0.0? |
| A | Zero bits (no subnet ID field). The mask 255.255.0.0 is the default condition for a Class B network. All 16 mask bits are used for the network ID, and no bits are available for subnetting. |
| Q. | Why would a software developer use UDP for a transport protocol when TCP offers better quality assurance? |
| A. | TCP’s quality assurance comes at the price of slower performance. If the extra error control and flow control of TCP are not necessary, UDP is a better choice because it is faster. |
| Q. | Why is the third step in the TCP three-way handshake necessary? |
| A. | After the first two steps, the two computers have exchanged ISN numbers, so theoretically they have enough information to synchronize the connection. However, the computer that sent its ISN in step 2 of the handshake still hasn’t received an acknowledgment. The third step acknowledges the ISN received in the second step. |
| Q | What is the role of a resolver? |
| A | A resolver passes name resolution requests between the applications on a system and DNS servers. |
| Q | What is a hostname? |
| A | It is a single name that is assigned to a particular host. Usually the hostname has some meaning such as location, usage, or ownership. |
| Q | When I bring my laptop to an Internet cafe, I can’t send email messages with the email account I use at the office. How can I stay in contact with coworkers when I stop for a latte? |
| A | Corporate networks often block outside access to the SMTP server to prevent spammers from accessing the mail server. If you have access to a webmail account, try using it from the Internet cafe instead. You could also ask your system administrator for a VPN account, which would allow you to connect to the local network from outside the firewall. |
| Q | I can connect with remote websites by IP address but not by URL. What is wrong? |
| A | Sounds like a name resolution problem. Check your configuration to ensure that your system is configured to use a DNS server. If so, ping the DNS server to ensure that you’re connected. |
| Q. | I need to make several legacy network applications work on a Windows XP computer. I have been instructed to provide confidentiality for communication using these ancient apps. Should I use SSL or IPSec? |
| A. | SSL operates above the Transport layer, so an application that uses SSL must be aware of the SSL interface. IPSec, on the other hand, operates lower in the stack. The application doesn’t have to know about IPSec. In this case, try IPSec. |
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