TCP/IP Model Overview - USALearning

TCP/IP Model OverviewTable of ContentsOSI Model vs. TCP/IP Model . 2TCP/IP Model . 3TCP/IP Layer 1 – Physical . 4TCP/IP Layer 2 – Data-link . 5TCP/IP Layer 3 – Network . 6TCP/IP Layer 4 – Transport . 7TCP/IP Layer 5 – Application . 8TCP/IP Model . 9TCP/IP Model – Sender -1 . 12TCP/IP Model – Sender -2 . 13TCP/IP Model – Sender -3 . 14TCP/IP Model – Sender -4 . 15TCP/IP Model – Sender -5 . 16TCP/IP Model – Data Transmitted . 17TCP/IP Model – Receiver -1 . 18TCP/IP Model – Receiver -2 . 19TCP/IP Model – Receiver -3 . 20TCP/IP Model – Receiver -4 . 21TCP/IP Model – Receiver -5 . 22Notices . 23Page 1 of 23

OSI Model vs. TCP/IP ModelOSI Model vs. TCP/IP icalPhysicalOSI ModelTCP/IP Model“Please Do not Throw Sausage Pizza Away”30**030 Okay so now let's map to theother model that's out there.Page 2 of 23

TCP/IP ModelTCP/IP ModelA framework for data communicationDe facto standard for networkingArchitecture independent – the layersabstract the details from higher levelsNot originally designed to handlesecurity tasks – tacked on as separateprotocols within the modelApplicationTransportNetworkData-link*Other interpretations of the TCP/IP model donot include a physical layerPhysical31**031 So let's talk about the wholemodel first before we actually dig anydeeper.It is another framework for dataCommunication.Now it was never designed at thevery beginning to handle the security.It just-- it wasn't- that wasn't anissue as it was birthed. But now thatis an issue. And so we've revved theprotocol from version 4 to version 6.There is no version 5 of TCP/IP.Page 3 of 23

TCP/IP Layer 1 – PhysicalTCP/IP Layer 1 – PhysicalApplication Transmits logical bits (1’s and0’s) over a physical circuit Electrical and physicalspecificationsTransportNetwork Equivalent to Physical layer inOSI modelData-linkPhysical32**032 So let's look at it.Physical layer; same thing:Transmitting the bits; electricalsignals; Physical specification. Soidentical to the OSI.Page 4 of 23

TCP/IP Layer 2 – Data-linkTCP/IP Layer 2 – cal Physical addressing, errordetection and reliable datatransfer Also referred to as the networkaccess layer Equivalent to Data-link layer inOSI model Devices – ATM, switches,bridges Protocols: PPP, ARP33**033 Data-link layer; same thing.Now we're talking about havingPhysical addressing that was burnedinto the network card itself, that MACaddress. We're using that overagain. And we also pay attention toARP; and that allows us to map theData-link to the Network layer.Page 5 of 23

TCP/IP Layer 3 – NetworkTCP/IP Layer 3 – NetworkApplication Logical addressing, routeselection Fragmentation and re-assemblyTransportNetworkData-linkPhysical Equivalent to Network layer inOSI model Devices – Layer 3 bridges,routers Protocols: IP, ICMP, IPSec34**034 TCP Network layer. Samething all over again. Same kind oflogical addressing.Routed protocols versus routingprotocols. Routed protocols meansthe data is being transmitted fromhost to host. Routing protocolsmeans that when we're talking aboutthe routers that are in the way thatwe route around the congestion.We'll talk about those in a bit.Page 6 of 23

TCP/IP Layer 4 – TransportTCP/IP Layer 4 – TransportApplication End-to-end connections, flowcontrol and reliability Equivalent to Transport layer inthe OSI modelTransport Protocols: TCP, UDPNetworkData-linkPhysical35**035 Transport Layer. Again thesame thing. At the Transport layerfor TCP there are definitely only twoprotocols: TCP and UDP.Page 7 of 23

TCP/IP Layer 5 – ApplicationTCP/IP Layer 5 – Application User applications, data shapingApplicationTransportNetwork Equivalent to Session,Presentation, and Applicationlayers in OSI model Protocols: DHCP, HTTP, Telnet,FTP, SMTPData-linkPhysical36**036 At the Application layer it allgot jammed together-- Session,Presentation and Application-- whenwe look at the protocols that are there.These are the same protocols thatwere in the OSI. But the problemwas is we didn't quite know whatlayer to put Dynamic HostConfiguration protocol. We didn'tquite know where to put SMTP;because it's not really an end-usermail protocol, unless you're POPingor IMAPing in. I mean, yes you canSMTP back. But we didn't quite knowwhere to put those in the OSI modelbecause they kind of bled into all thedifferent layers.Page 8 of 23

And so that's why TCP/IP, from animplementation standpoint, is actuallya better model; because thoseabstractions that had to be done atlayer after layer after layer, thosethree layers there, could all besatisfied by one executable or oneDLL. And so it makes it a little biteasier for us to wrap them alltogether into the Application layer;and we leave all that stuff there.TCP/IP ModelTCP/IP ModelData passes through each layer in the model. Top-down (sender) and bottom-up (receiver) Sender transmits data in small pieces— Segments/datagrams, packets, frames, bits Network transfers data to destination— Reliably (TCP) or not (UDP) Destination reassembles data— Error correction, retransmission as 37**037 Now when we talk about TCPmodel-- and you could say the exactsame thing for the OSI model; and sowhat we're going to do is we're goingto leave OSI behind and we're goingPage 9 of 23

to only focus on TCP/IP pretty muchfor the rest of this session.When you've passed the data downor up the stack, what happens isencapsulation or de-encapsulation.As we move up and down the layers,we call the name of the protocol dataunit at that layer something distinct.So at the Physical layer it's calledbits; at the Data-link layer-- let's seeit's-- the way to do this is to talkabout bits, frames, at the Data-linklayer.Very rarely do we hear that; becausepeople don't talk about the framesanymore: Well there's a problem withthe frames.The problem is is that everybody saysone universal word when they'retalking about non-application layerprotocols, in most cases; they say theword 'packet'. And so we accept thatfrom the rest of the world; but wewant to be a little bit more specifichere.And what happens with theseprotocol data units is at the framelevel we do these kinds of activities.If we have a frame problem, weknow it's not an end-user issue; it'ssomething either wrong with thestack or it's something wrong withour resolution.Now what happens in TCP model iswe pass through each one of theselayers; and each one of theseprotocol data units, or names forPage 10 of 23

things at that layer, does itsparticular purpose; and then it's set itand forget it for the other layers.When I do all my frame work at theData-link layer, the Physical layerknows it needs to give it to me in acertain format. But that's prettymuch it; and it de-encapsulates andhands that frame to me.I look at this frame and I take myaction. I de-encapsulate; and then Ipass that up to the Network layer.So as we send and transmitsegments, packets, data, frames,bits, when we start doing thistransmission back and forth we usethose constructs.Page 11 of 23

TCP/IP Model – Sender -1TCP/IP Model – Sender -1Data is “encapsulated” as it makes its way through the rkData-linkPhysicalWireWire38**038 So as we pass down thestack we're going to add information.We're going to encapsulate.Page 12 of 23

TCP/IP Model – Sender -2TCP/IP Model – Sender -2Data is “encapsulated” as it makes its way through the rtNetworkData-linkPhysicalWireWire39**039 So from the Application layerwe have pure data. At the Transportlayer we add in the TCP headerinformation that is valid fortransmitting to the host on the otherside.Page 13 of 23

TCP/IP Model – Sender -3TCP/IP Model – Sender -3Data is “encapsulated” as it makes its way through the portTCPDataNetworkData-linkPhysicalWireWire40**040 At the Network layer we addin the IP header information.Now at the Network layer, by theway, we don't know that there's TCPand data as separate things. Wetreat it all like data.So you could- here you could crossoff the word TCP and data at thislayer and just write the word data;and that would be accurate becausethe IP layer, the Network layer, doesnot know anything about thepreceding headers above it.When it passes it down thestack again, this all becomes data.Page 14 of 23

TCP/IP Model – Sender -4TCP/IP Model – Sender -4Data is “encapsulated” as it makes its way through the Wire41**041 And at the Data-link layer weadd the header information of the source anddestination MAC address; and wealso add a trailer at this point, whichis the Cyclical Redundancy Checking-CRC or FCS if you're a Cisco person.So we actually do encapsulation onboth sides.Page 15 of 23

TCP/IP Model – Sender -5TCP/IP Model – Sender -5Data is “encapsulated” as it makes its way through the Wire42**042 At the Physical layer whatwe're doing is we're converting it intosignal. We're converting it- forcopper we're converting it intoelectronic charges of 1s and 0s, on'sand off.If we're converting it over to fiber,then what we're doing is is we'returning it into light pulses at thatpoint. And that gets a little bitbeyond- how the light pulses workgets beyond what we do here.We pass it across the wire asa whole.Page 16 of 23

TCP/IP Model – Data TransmittedTCP/IP Model – Data TransmittedData is transmitted across the PTCPDataWire43**043 So on the wire it looks likeall 1s and 0s.Page 17 of 23

TCP/IP Model – Receiver -1TCP/IP Model – Receiver -1Data is “de-encapsulated” as it makes its way through DLPhysicalDLWireIPTCPDataWire44**044 But when it gets to thereceiving host on the other side, itsays: Oh I know what to do withthat; that is destined for me basedupon my MAC address; or basedupon the broadcast. I'm going totake care of that and I'm going to ripoff the Data-link layer information.Page 18 of 23

TCP/IP Model – Receiver -2TCP/IP Model – Receiver -2Data is “de-encapsulated” as it makes its way through DataTCPIPDLPhysicalDLWireIPTCPDataWire45**045 And I'm going to pass it upthe stack; and I'll trust that theNetwork layer knows what to do withthis. Because I knew what to do, mypart, and I'm done my part; and Ipass it up the stack.Page 19 of 23

TCP/IP Model – Receiver -3TCP/IP Model – Receiver -3Data is “de-encapsulated” as it makes its way through 46 Same thing with theTransport layer. The IP layer isripped off; and now it makes TCPdecisions.Page 20 of 23

TCP/IP Model – Receiver -4TCP/IP Model – Receiver -4Data is “de-encapsulated” as it makes its way through 7**047 Finally it gets to the top ofthe food chain, where it's now dataat that point, and now we've strippedoff all the header information; andthe Application is going to makeprobably some sort of presentationactions that occur at that point.Page 21 of 23

TCP/IP Model – Receiver -5TCP/IP Model – Receiver -5Data is “de-encapsulated” as it makes its way through 8**048 So we've got a sender and areceiver; an encapsulation as we godown, a de-encapsulation as we go up.Page 22 of 23