1. CCNA Guide to Cisco Networking Fundamentals Fourth Edition
Chapter 3
TCP/IP

2. Objectives Discuss the origins of TCP/IP
Identify and discuss the different layer functions of TCP/IP
Describe the functions performed by protocols in the TCP/IP protocol suite, including ICMP, UDP, TCP, ARP, and RARP
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

3. Objectives (continued)
Use Ping and Trace and describe their functions
Explain how packets are transmitted
Describe the Cisco three-layer hierarchical model
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

4. Origins of TCP/IP
Transmission Control Protocol/Internet Protocol (TCP/IP)
Resulted from a coordinated effort by the U.S. Department of Defense (DOD)
Advanced Research Projects Agency (ARPA)
Charged with creating a wide area network (WAN)
Results were TCP/IP and ARPANET
DOD funded two projects
The adaptation of TCP/IP to work with UNIX
The inclusion of the TCP/IP protocol with Berkeley UNIX (BSD UNIX)
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

5. Overview of the TCP/IP Protocol Suite
The TCP/IP model explains how the protocol suite works to provide communications
Four layers: Application, Transport, Internetwork, and Network Interface
Requests for Comments (RFCs)
Define, describe, and standardize the implementation and configuration of the TCP/IP protocol suite
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

6. CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

7. Application Layer Protocols at the TCP/IP Application layer include:
File Transfer Protocol (FTP)
Trivial File Transfer Protocol (TFTP)
Network File System (NFS)
Simple Mail Transfer Protocol (SMTP)
Terminal emulation protocol (telnet)
Remote login application (rlogin)
Simple Network Management Protocol (SNMP)
Domain Name System (DNS)
Hypertext Transfer Protocol (HTTP)
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

8. Transport Layer
Performs end-to-end packet delivery, reliability, and flow control
Protocols:
TCP provides reliable, connection-oriented communications between two hosts
Requires more network overhead
UDP provides connectionless datagram services between two hosts
Faster but less reliable
Reliability is left to the Application layer
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

9. Transport Layer (continued)
Ports
TCP and UDP use port numbers for communications between hosts
Port numbers are divided into three ranges:
Well Known Ports are those from 1 through 1,023
Registered Ports are those from 1,024 through 49,151
Dynamic/Private Ports are those from 49,152 through 65,535
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

10. CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

11. Transport Layer (continued)
TCP three-way handshake
Establishes a reliable connection between two points
TCP transmits three packets before the actual data transfer occurs
Before two computers can communicate over TCP, they must synchronize their initial sequence numbers (ISN)
A reset packet (RST) indicates that a TCP connection is to be terminated without further interaction
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

12. CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

13. CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

14. CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

15. Transport Layer (continued)
TCP sliding windows
Control the flow and efficiency of communication
Also known as windowing
A method of controlling packet flow between hosts
Allows multiple packets to be sent and affirmed with a single acknowledgment packet
The size of the TCP window determines the number of acknowledgments sent for a given data transfer
Networks that perform large data transfers should use large window sizes
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

16. Transport Layer (continued)
TCP sliding windows (continued)
Other flow control methods include
Buffering
Congestion avoidance
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

17. Internetwork Layer Four main protocols function at this layer ARP
Internet Protocol (IP)
Internet Control Message Protocol (ICMP)
Address Resolution Protocol (ARP)
Reverse Address Resolution Protocol (RARP)
ARP
A routed protocol
Maps IP addresses to MAC addresses
ARP tables contain the MAC and IP addresses of other devices on the network
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

18. Internetwork Layer (continued)
ARP (continued)
When a computer transmits a frame to a destination on the local network
It checks the ARP cache for an IP to MAC address mapping for the destination node
ARP request
If a source computer cannot locate an IP to MAC address mapping in its ARP table
It must obtain the correct mapping
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

19. Internetwork Layer (continued)
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

20. Internetwork Layer (continued)
ARP request (continued)
A source computer broadcasts an ARP request to all hosts on the local segment
Host with the matching IP address responds this request
ARP request frame
See Figure 3-7
ARP cache life
Source checks its local ARP cache prior to sending packets on the local network
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

21. Internetwork Layer (continued)
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

22. Internetwork Layer (continued)
ARP cache life (continued)
Important that the mappings are correct
Network devices place a timer on ARP entries
ARP tables reduce network traffic
Reverse Address Resolution Protocol (RARP)
Similar to ARP
Used primarily by diskless workstations
Which have MAC addresses burned into their network cards but no IP addresses
Client’s IP configuration is stored on a RARP server
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

23. Internetwork Layer (continued)
RARP request frame
See Figure 3-8
RARP client
Once a RARP client receives a RARP reply, it configures its IP networking components
By copying its IP address configuration information into its local RAM
ARP and RARP compared
ARP is concerned with obtaining the MAC address of other clients
RARP obtains the IP address of the local host
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

24. CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

25. Internetwork Layer (continued)
ARP and RARP compared (continued)
The local host maintains the ARP table
A RARP server maintains the RARP table
The local host uses an ARP reply to update its ARP table and to send frames to the destination
The RARP reply is used to configure the IP protocol on the local host
Routers and ARP
ARP requests use broadcasts
Routers filter broadcast traffic
Source must forward the frame to the router
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

26. Internetwork Layer (continued)
ARP tables
Routers maintain ARP tables to assist in transmitting frames from one network to another
A router uses ARP just as other hosts use ARP
Routers have multiple network interfaces and therefore also include the port numbers of their NICs in the ARP table
The Ping utility
Packet Internet Groper (Ping) utility verifies connectivity between two points
Uses ICMP echo request/reply messages
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

27. Internetwork Layer (continued)
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

28. Internetwork Layer (continued)
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

29. Internetwork Layer (continued)
The Trace utility
Uses ICMP echo request/reply messages
Can verify Internetwork layer (OSI-Network layer) connectivity
Shows the exact path a packet takes from the source to the destination
Accomplished through the use of the time-to-live (TTL) counter
Several different malicious network attacks have also been created using ICMP messages
Example: ICMP flood
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

30. Internetwork Layer (continued)
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

31. Network Interface Layer
Plays the same role as the Data Link and Physical layers of the OSI model
The MAC address, network card drivers, and specific interfaces for the network card function at this level
No specific IP functions exist at this layer
Because the layer’s focus is on communication with the network card and other networking hardware
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

32. Understanding Frame Transmission
Each host on a segment evaluates the frame
To determine whether the listed destination MAC address matches its own or is a broadcast to all hosts
The host makes a copy of the frame and sends the original along the network path
On the destination host, frames are sent up the TCP/IP stack
Removing each layer header information
For a packet to be routed on a TCP/IP internetwork
An IP address and MAC address are required for both the source and destination hosts
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

33. Routers on the Network A router requires:
An IP address for every network segment to which it is connected
A separate network interface or port for each network segment
Computers send frames to destinations that are not on their segment to the router (default gateway)
The router must determine which subnet should receive the frame
The router references its routing table
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

34. Routers on the Network (continued)
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

35. Network to Network
Routers maintain routing tables that they use to route packets from one network to another
When a network uses TCP/IP, each port on a router requires an IP address
Allows the router to correctly forward the packet to the appropriate network segment
On a TCP/IP network, the logical addresses on a certain segment must be matched
If you move a computer from one segment to another, the IP address will have to be changed
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

36. Network to Network (continued)
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

37. Dynamic or Static Tables
Routing tables match network addresses with the addresses of the routers that handle those networks
The tables can be built statically or dynamically
Dynamic updates are provided through routing protocols
A router capable of dynamic routing can choose from among the various routes on a network
The router communicates with other dynamic routers
To determine the most efficient route from one point to another on the network
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

38. Dynamic or Static Tables (continued)
Methods to determine the best path across a network
The distance-vector algorithm
The link-state algorithm
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

39. Transmitting Packets to Remote Segments
When TCP/IP hosts transmit packets to remote segments
They contact their default gateway (usually a router)
The router checks its routing tables against the destination IP address
To locate the appropriate network interface through which to forward the packet
Router re-addresses the frame or sends the packet to the next router in the path (indirect routing)
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

40. Routing Packets
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

41. Routing Packets (continued)
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

42. Routing Packets (continued)
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

43. Routing Packets (continued)
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

44. The Cisco Three-Layer Hierarchical Model
Does not describe how communications take place
Focuses on how best to design a network
Especially a relatively large network or one that is expected to grow
Each layer of the model is involved in specific functions
Is typically defined by a particular type of device
The three layers of the model from bottom up are Access, Distribution, and Core
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

45. CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

46. Access Layer
The layer closest to the users, where they attach to the network
Could be a router if the network is very small
But typically a hub or layer 2 switch
Sometimes called the desktop layer because it deals with connecting workstations to the network
Frames are delivered to the users at this layer
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

47. Distribution Layer Separates the Access layer from the Core layer
Implements network policies, and provides many networking services
Such as Network Address Translation (NAT), firewall protection, and quality of service (QoS)
IP addressing hierarchy is managed at this layer
IP addressing is the process of assigning unique IP addresses to devices on the network
Typically involves routers and includes all of the router functions
Provides almost all of the connectivity tasks
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

48. Core Layer
Responsible for switching large amounts of data quickly and efficiently
To prevent slowing down the switching process:
This layer should not be burdened with security or traffic control measures or any unnecessary additional equipment
The primary device at this layer is a high-end layer 3 switch
Essentially the backbone of the network
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

49. Summary
TCP/IP is not limited to transmission control and Internet protocols
TCP/IP was started by the Defense Advanced Research Projects Agency (DARPA)
TCP/IP maps to a four-layer network model: Application, Transport, Internetwork, and Network Interface
The Application layer in the TCP/IP model covers the Application, Presentation, and Session layers of the OSI reference model
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

50. Summary (continued)
The TCP and UDP protocols reside at the Transport layer of the TCP/IP networking model
Both TCP and UDP use port numbers from 1 to 65,535 to establish their communications between two points
The Internet Protocol (IP) resides at the Internetwork layer and provides the logical address that can be passed through a router
You can use the Ping utility with IP and ICMP to diagnose and troubleshoot network connections
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition

51. Summary (continued)
Address Resolution Protocol (ARP) and Reverse ARP (RARP) reside in the Internetwork layer
The MAC address is the final leg of communication between hosts
Routing tables can be created manually and dynamically
Cisco developed the Three-Layer Hierarchical model to help network administrators design more efficient networks
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition