BROCADE IP PRIMER

Console49F Link 50F1 3 5 7 9 1113 15 17 19 21 23 25 27 29 31 33 3537 39 41 43 45 47Power1F 2F 3F 4F2 4 6 8 10 1214 16 18 20 22 24 26 28 30 32 34 3638 40 42 44 46 4849F Link 50FPowerConsole1 3 5 7 9 1113 15 17 19 21 23 25 27 29 31 33 3537 39 41 43 45 471F 2F 3F 4F2 4 6 8 10 1214 16 18 20 22 24 26 28 30 32 34 3638 40 42 44 46 48Thinking in BinaryI mentioned earlier that there are other Network Layer protocols in IP. Here area couple of the more well-known ones:Internet Control Message Protocol (ICMP) is used to send messages betweenLayer 3 devices. It can check to see if an address is responding. It can tellanother Layer 3 address that it's sending information too fast. It can help tracethe path through several routers. The most common use for ICMP is its echoprotocol, more commonly known as ping. This is a really simple protocol. Onedevice will send an “echo request” message to another device. If that device isactive, it will send an “echo reply” back to the first device. Simply stated, it's asif one device shouts out, “Hey, are you there?” And if the device is there, itresponds with, “Yeah, I'm here!”Hey, are you there?ICMP Echo RequestYeah, I’m here!ICMP Echo ReplyAddress Resolution Protocol (ARP) is used to match an IP address with a MACaddress. It kind of bridges the gap between the Data Link Layer and the NetworkLayer. We'll talk more about ARP later in the chapter.Thinking in BinaryThe numbers that we use in our daily lives (with rare exception) are decimal.This means base 10. What does “base 10" mean? It means we have ten digits(single numbers) we can use before we have to start using two digits. Forexample, we have the number 0 (zero). That's one number. We also have nineother numbers: 1, 2, 3, 4, 5, 6, 7, 8, and 9. If we're going to represent anynumber higher than that, we need to start using two-digit numbers (e.g., 10,11, 12, etc.). That's decimal, or base 10.Computers, overly simplified, are made of up of billions of transistors. Transistorsare electrical components that can be in one of two states. There's eithera voltage (electricity is passing through them), or there is no voltage (no electricityis passing through them). You can think of transistors like a light switch.The light switch is either on, or it's off. You've got two options.It didn't take computer engineers long to realize that they could use this anomalyto count. But we can only really represent two numbers: 0 (off) and 1 (on).So, how can that be useful? Well, if you're only talking about a single digit, itreally isn't very useful. But when you string a bunch of digits together, now youcan represent all kinds of numbers.Brocade IP Primer 39