CIM 2465 Intro to TCP/IP1 Introduction to TCP/IP (Topic 5) Textbook: Networking Basics, CCNA 1...

transcript

CIM 2465 Intro to TCP/IP 1

Introduction to TCP/IP(Topic 5)

Textbook:

Networking Basics, CCNA 1 Companion Guide, Cisco Press

Cisco Networking Academy Program, CCNA 1 and 2, Companion Guide, Cisco Press, Latest Edition

TCP/IP Model

• TCP/IP was first developed as part of a contract from the US DoD

OSI Model TCP/IP ModelApplication

Presentation Application

Session

Transport Transport

Network Internet

Data Link

Physical Network Access

TCP/IP Network Access Layer (1)

• Also known as Network Interface Layer• Defines how computers and networking devices

should access a physical medium to send bits to others

• Match OSI Layers 1 and 2• Does not actually define any network access

layer standards, but refers to other well-defined standards

• Note that ARP, proxy ARP, and RARP mainly work at TCP/IP’s internet layer, but they provide an interface to the network access layer

TCP/IP Network Access Layer (2)

• Fig 9-2

TCP/IP Internet Layer

• Defines how to deliver data from one host to another (over multiple different physical networks)

• By separating its logic from the underlying networking details, thus allows hosts, networking devices, routers, to use the same processes and logic regardless of the underlying physical networks being used

• Logical Addressing (IP addresses for each network interface)

• Routing• Defines several protocols, most important being the

Internet Protocol (IP)

Key Internet Layer ProtocolsProtocol Description

Internet Protocol (IP) Defines routing, logical IP addressing, the format of IP headers and packets, and interfaces

Address Resolution Protocol (ARP)

Defines the process by which an IP host dynamically learns the mapping between another host’s IP address and its MAC address

Reverse Address Resolution Protocol (RARP)

Mostly unused today. Provides a basic method for IP address assignment

Internet Control Message Protocol (ICMP)

Defines messaging used to manage and control IP (e.g. used by the command ping)

Basic IP Routing

• IP routing defines how to forward data, in form of IP packets, from one host to another

• Fig 9-3

IP Packets

• An IP packet is the header defined by the IP protocol, along with any higher-layer protocol headers and the end-user data

• Basic IP Packet format

IP Header TCP/IP Transport & Application Layer Headers

End-user data

How IP Routing uses IP Addresses

• Routers use IP routing tables to tell them out which interfaces to forward packets

• To make routing efficient– IP addresses for hosts on the same physical

network must have the same value in the first part of the addresses (network address)

– Each group then need one entry in the routing table

• Fig 9-5

TCP/IP Transport Layer

• To provide the service of taking data from one application process on one computer and delivering that data to the correct application process on another computer

• Compare with the Internet Layer, the internet layer delivers data packets from one computer to another, but it does not think about which application sent the data or which application on the receiving computer needs the data

• Fig 9-6

• Two main Transport Layer protocols– Transmission Control Protocol (TCP)– User Datagram Protocol (UDP)

TCP Vs UDPTransport Layer Feature

Description TCP UDP

Segmentation of data

Breaking large chunks of data into network-legal sizes, call segments

Multiplexing using port numbers

Identifying application process (by port) that needs the data

Error recovery Monitoring for lost segments and resending them

In-order delivery of data

Monitoring received segments and putting them in correct order

Flow control Monitoring network performance and control the flow of data

TCP/IP Application Layer

• Provides services to applications

• Fig 9-7

Application Layer ProtocolsProtocol Description Transport Layer

Protocol

Hypertext Transfer Protocol (HTTP)

Defines the commands, headers, and processes by which web servers and web browsers transfer files

Trivial File Transfer Protocol (TFTP)

A very simple protocol that allows file transfer

File Transfer Protocol (FTP)

A very robust protocol used for transferring files

Application Layer ProtocolsProtocol Description Transport Layer

Protocol

Network File System (NFS)

A distributed file system protocol suite that allows remote file access across a network

Simple Mail Transfer Protocol (SMTP)

Defines the process by which e-mail my be forwarded and then held for later retrieval

Terminal Emulation (Telnet)

Defines the protocols used to allow a user to remotely access another computer

Application Layer ProtocolsProtocol Description Transport Layer Protocol

Simple Network Management Protocol (SNMP)

An application protocol usually used by the network management software to allow a network engineer to monitor and troubleshoot network problems

Domain Name System (DNS)

A protocol that defines how a computer may refer to another computer by name, instead of the IP address

Dynamic Host Configuration Protocol (DHCP)

A protocol used to dynamically assign IP addresses to hosts

TCP/IP Internetworks

Routing Fundamentals

• Routers have two main functions– Perform end-to-end delivery of IP packets

from the sending host to the receiving host.• Receive packets• Decide to which router or host to send the packets

next• Forward them

– Maintain a Routing Table with the best routes to reach each possible destination, using some routing protocols

IP Routing (1)

• Layer 2 devices, such as LAN switches, can forward data on only Ethernet links (within the same network), it cannot connect to WAN links (to other networks), as the physical and datalink standards are different

• Routers, can connect to multiple types of physical network (internetworking)

• So, routers can receive IP packets sent by computers and send the packets over any physical networks, to deliver the packets to the destinations. This forwarding process is called IP routing or IP forwarding

IP Routing (2)

• A router examines incoming packets, looks at the destination IP address, and decides out which interface to forward the packet

• Routing process relies on each router knowing how to route IP packets based on its IP routing table

• Routers use routing protocols (e.g. RIP, EIGRP), to dynamically learn the required routes

Some Key Terms

• Routing / Forwarding– The process of received packets, deciding where to

forward them next, and forwarding them

• Routed protocol / Routable protocol– A protocol that defines a packet that can be forwarded

by a routing process– E.g. IP, IPX (Netware) are routable, NetBEUI is non-

routable

• Routing protocol– A protocol used between routers so that they can

dynamically learn routes to add to their routing tables

Routing between Two Connected LAN Subnets

• The router has an interface physical attached to each of the two LANs

IP-Centric Perspective

No changes to source and destination IP address

• Note that the router will remove the Ethernet header/trailer and encapsulate a new one

Note the changes of MAC addresses

IP Routing: Host Perspective (1)

IP Routing: Host Perspective (2)• Decision

– If the destination IP address is on my same IP network/subnet, send the packet directly to that host

– If the destination IP address is not on my same IP network/subnet, send the packet to my default router (default gateway)

Main steps of IP routing

• P.400 of the textbook

More Detailed Routing Steps

Perspectives on WAN Routing• R1, R2 configured to use Serial interface and a

data link protocol PPP (Point-to-Point Protocol)

Important Characteristics of IP

• IP is Unreliable– The protocol does not attempt to perform any

error recovery of data (lost data)– How to have Reliable transmission

• Uses TCP transport layer protocol, which performs error recovery

• The application itself performs the error recovery

• IP is Connectionless

Connectionless Vs Connection-oriented

• Connectionless– The sender and receiver do not pre-arrange for

communication to occur– E.g. IP, Ethernet, UDP– Analogy: mailing a letter

• Connection-oriented– The sender and receiver must pre-arrange for

communication to occur– E.g. TCP, Frame Relay– Analogy: make a phone call

Full IP Header• Table 10-4 for details

Routing Protocols

• Used by routers to learn routes• When a collection of routers uses the

same IP routing protocol, the routers exchange messages and update their own routing tables

• HOW?– Connected subnets– Static Routes– Routing protocols

Learning Connected Routes• Subnets to which a router’s interfaces are connected are

called connected subnets• Routers automatically add routes to their IP routing

tables for directly connected subnets

means “Connected”

Static Routes

• Add routes to routing tables via router configuration

• E.g. a Cisco router command to R1 (interface FA0/1) of Fig 10-11ip route 172.16.3.0 255.255.255.0 172.162.2.252

will add an entry to R1

S 172.16.3.0 255.255.255.0 Fa0/1 172.16.2.252

(S means “Static”)

Learning by Routing Protocols

• Each router sends messages to the routers attached to the same subnets, which essentially list all the routing information each router knows. Thus all routers learns all the routes.

RIP (Routing Information Protocol)• R2 knows a connected route to 172.16.3.0, so

RIP then advertises this route to R1

Using Metrics to Pick the Best Routes

• Routing protocols must be able to choose between competing alternative routes

Using Metrics to Pick the Best Routes

• By Metric, some kind of measurement• Allows a router to measure how good each route is

– Hop Count (RIP)– Bandwidth, Delay, Loading, Reliability (IGRP, EIGRP)– Cost (OSPF)– Clock Ticks (Novell IPX)

Routing Protocol Metrics

Routing Protocol Algorithms

• Distance Vector Algorithms– “distance to neighboring routers” as the metric

(e.g. Hop count in RIP)– No information about the topology of the

network beyond the neighboring routers

• Link State Algorithms– Advertise information about the entire topology– Shortest Path Algorithm

• Hybrid Algorithms

Classless Vs Classful Routing Protocols

• Variable-length Subnet Masking (VLSM)– Provides a great deal of flexibility when subnetting a sin

gle Class A, B, or C network– Different subnet masks can be used on different subnet

s of the same Class A, B, or C network– Allows network engineers to reduce the number of wast

ed IP addresses

• A Classful routing protocol does not send subnet masks in routing updates, so it cannot support VLSM

• A Classless routing protocol does send subnet masks in routing updates, so it does support VLSM

CIM 2465 Intro to TCP/IP1 Introduction to TCP/IP (Topic 5) Textbook: Networking Basics, CCNA 1...

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