IP, NAT and PAT Table of Contents IP ..................................................................................................................................................... 2 IP Classes ......................................................................................................................................... 5 IP Addresses of Note ....................................................................................................................... 7 NAT and PAT ................................................................................................................................... 9 Notices .......................................................................................................................................... 11 Page 1 of 11 IP IP Internet Protocol (OSI Layer 3) • Sends packets over a network, used for addressing and routing • No guarantee of delivery, only best effort IP addressing • IPv4 address is 32-bits in length • 192.168.1.1 11000000 . 1010100 . 00000001 . 00000001 • Each number between periods is an “octet” between 0 and 255 • Reflects both the network, and the host address — These numbers are separated out by the subnet mask 128 **128 We're talking about first Internet protocol. Now, we're talking about Internet protocol version four at this moment in time, which is at layer three. We're also going to switch over to IPv6 in just a second. In v4, you have to know how big the address is in bits. Even though it's converted into decimal form, you need to think about it in terms of bits because then when we deal with subnet masking and when we deal with routing tables, we have to know how this conversion works in our head. So, when we convert this what we do is we do it in octets. That's four sets Page 2 of 11 of eight. And each IP address piece, each octet, is a number between two fifty-five and zero. Now, we don't use two fifty-five. And we don't use zero. That's the first and the last address because we use them for something else. But all of the other addresses area valid. And by the way, two fifty- five would be ones all the way across the bits. And zero would be zero all the way across the bits in that octet. So, right here we have an example of 192.168.1.1. Well, the first two bits are turned on in a thirty-two bit address. That's the one twenty-eight bit is the first bit. And the second bit is the sixty-four bit. Sixty-four plus one twenty-eight equals one hundred and ninety-two. The math works. The one sixty-eight address, the first bits turned on. That's one hundred twenty-eight. We'll keep that in our head. The second one is turned off, so we skip over the sixty four. And then the next bit is thirty-two. And that one's turned on. Well, not all of them are turned off. So, we've got one twenty-eight plus thirty-two. Let's see one twenty-eight plus thirty- two, that's a hundred and sixty. We count down a couple more bits, and we get to the third bit in that list. It's turned on. That's the eight bit. So, eight plus one hundred and sixty is one hundred and sixty-eight. Hey look, the math works. And then the other two, one and one. I mean we don't have to worry about those two, right? We're good for that. You get the idea that we have to know this and convert this in our head every Page 3 of 11 once and a while, not often, but every once and a while. So, we're also looking at the network address and the host address, and which are the portions here one versus the other. And these numbers are separated by the subnet mask. In this case, for a 192.168.1.255, that would be the network address. And what that says is all the numbers, the first three octets must stay the same. The subnet mask for this to tell us that this is a particular network is going to be 255.255.255, and what that says is-- I'm sorry, 255.255.255.0. That says everything in this octet has to be the same. Everything in the next octet has to be the same. Everything in the next octet has to be the same. So, if we want to communicate on the same network, you better be in the 192.168.1 and then change the numbers in the last octet. Page 4 of 11 IP Classes IP Classes Number Addresses Start Class End address of networks per network address Class A 128 (27) 16,777,216 (224) 0.0.0.0 127.255.255.255 Class B 16,384 (214) 65,536 (216) 128.0.0.0 191.255.255.255 Class C 2,097,152 (221) 256 (28) 192.0.0.0 223.255.255.255 Class D 224.0.0.0 239.255.255.255 (multicast) Class E 240.0.0.0 255.255.255.255 (reserved) 129 **129 There are different classes of IP addresses. A, B, and C are the normal classes. When we talk about the start and end address, some of the hosts that are in there, some of the numbers that are in there, are not valid. But we are talking about what is the extent of this network. Well, in a class A network what we do is we fix the first octet. And then we mess with the rest of them. So, we have a hundred and twenty-eight class A networks that are available. When we go down to the class B set of addresses, the first octet and the first bit is fixed. If you convert one Page 5 of 11 twenty-eight into decimal, you see that it is a one followed by a zero. In a class C address, we have two million networks. But each one of those networks only has two hundred and fifty-six hosts on it. So, the first two bits will be fixed. One, one, zero makes up one ninety-two. And then anything below that is configurable. What about the class D and the class E? Well, first off the class E is experimental. And it's not used. Any address that came to you that was, "Hi, I'm from 240.1.1. You're not from anywhere that I really want to know about. I'm putting you on the bogon list, and all those addresses are no good because we don't play experiments with the Internet. Okay, I can go ahead and lop those off. The class D is the multicast address. This is IGMP not ICMP. And you'll know that it is a class D address because it is just shy of two forty, between two twenty-four and just shy of two forty, at two thirty-nine trip two fifty-five. That class D is for multicasting. Page 6 of 11 IP Addresses of Note IP Addresses of Note Private IP spaces are not routable on the open Internet • Intended for organizations to use instead of public (costly) IP addresses Private Address Start Address End Address Space Class A 10.0.0.0 10.255.255.255 Class B 172.16.0.0 172.31.255.255 Class C 192.168.1.0 192.168.1.255 127.0.0.0 127.255.255.255 – loopback address 169.254.0.0 169.254.255.255 – autoconfiguration 130 **130 There are a set of private IP address-- well, the IP address space that is limited by rule RFC 1918. And in it what it says is that we've got a group of IP addresses, because we're running out of IP addresses, what we're going to do is allow you to do internal IP address assignments back in here that we don't care about on the Internet. And, in fact, all of the routers that are RFC 1918 compliant won't even pass that traffic. So, what can we use back here that's not routable on the Internet or is not supposed to be? Well, there's one for each class of address. In the class A, it's the ten network, the entire ten Page 7 of 11 network. Sixty million hosts are useable inside your organization. But not on the Internet. Class B is a little bit different. It's the 172.16, just shy of the 172.32. That's a class B network that is totally useable by you. And actually there are sixty-five thousand hosts sixteen different times that are useable. So, you could have a sixteen, a seventeen, an eighteen, a nineteen, a twenty, all the way up to thirty-one. Those are all Class B addresses. They are not supposed to be routable. Last is the Class C address. Now, there's a funny little thing about the Class C address. The 192.168.1.0 through 255 is a class A address with only two hundred and fifty-four hosts on it. However, that's by convention. If you try to use the 192.168.2, three, four, all the way up to two- fifty-five. Those are also non-routable and not used. But the convention is 1.0. Now, there are two other special addresses that we want to pay attention to that aren't inside of the RFC 1918, but these are very good lists of hosts to not allow on your network filtered at your router or firewall. And that is the loopback address, the entire class A address of one twenty-seven-- we only use 127.0.0.1 as our loopback. The other ones don't count. They're not useable. And lastly, Microsoft created something called automatic IP Page 8 of 11 addressing, or APIPA, where they disqualified the entire 169.254 all the way up through 255.255.