74 PART I Networking Basics have little to do directly with how TCP/IP protocols or the Internet operates. For exam- ple, a full exploration of all the connector types used with fiber-optic cable would take many pages, and yet add little to anyone's understanding of TCP/IP or the Internet. Instead, we will concentrate on the structure of the frames sent on these link types, which are often important to TCP/IP, and present some operational details as well. ILLUSTRATED NETWORK CONNECTIONS We will start by using Ethereal (Wireshark), the network protocol analyzer introduced in the last chapter, to investigate the connections between systems on the Illustrated Network. It runs on a variety of platforms, including all three used in the Illustrated Network: FreeBSD Unix, Linux, and Windows XP. Ethereal can display real-time packet interpretations and, if desired, also save traffic to files (with a variety of formats) for later analysis or transfer to another system. Ethereal is most helpful when examining all types of Ethernet links. The Ethernet links are shown as dashed lines in Figure 3.1. The service provider networks' SONET links are shown as heavy solid lines, and the DSL link to the home office is shown as a dotted line. The wireless network inside the home is not given a distinctive representation in the figure. Note that ISPs today typi- cally employ more variety in WAN link types. Displaying Ethernet Traffic On the Illustrated Network, all of the clients and servers with detailed information listed are attached to LANs. Let's start our exploration of the links used on the Illus- trated Network by using Ethereal both ways to see what kind of frames are used on these LANs. Here is a capture of a small frame to show what the output looks like using tethe- real, the text-based version of Ethereal. The example uses the verbose mode ( ­V ) to force tethereal to display all packet and frame details. The example shows, highlighted in bold, that Ethernet II frames are used on LAN1. [root@lnxserver admin]# /usr/sbin/tethereal ­V Frame 2 (60 bytes on wire, 60 bytes captured) Arrival Time: Mar 25, 2008 12:14:36.383610000 Time delta from previous packet: 0.000443000 seconds Time relative to first packet: 0.000591000 seconds Frame Number: 2 Packet Length: 60 bytes Capture Length: 60 bytes Ethernet II, Src: 00:05:85:88:cc:db, Dst: 00:d0:b7:1f:fe:e6 Destination: 00:d0:b7:1f:fe:e6 (Intel_1f:fe:e6) Source: 00:05:85:88:cc:db (Juniper__88:cc:db) Type: ARP (0x0806) Trailer: 00000000000000000000000000000000...