• No results found

Guide to TCP/IP, Third Edition. Chapter 3: Data Link and Network Layer TCP/IP Protocols

N/A
N/A
Protected

Academic year: 2021

Share "Guide to TCP/IP, Third Edition. Chapter 3: Data Link and Network Layer TCP/IP Protocols"

Copied!
52
0
0

Loading.... (view fulltext now)

Full text

(1)

Guide to TCP/IP, Third Edition

Chapter 3:

Data Link and Network Layer TCP/IP

Protocols

(2)

Objectives

• Understand the role that data link protocols, such as SLIP and PPP, play for TCP/IP

• Distinguish among various Ethernet and token ring frame types

• Understand how hardware addresses work in a

TCP/IP environment, and the services that ARP

and RARP provide for such networks

(3)

Guide to TCP/IP, Third Edtion 3

Objectives (continued)

• Appreciate the overwhelming importance of the Internet Protocol (IP), and how IP packets behave on TCP/IP networks

• Understand the lifetime of an IP datagram, and the process of fragmentation and reassembly

• Appreciate service delivery options

• Understand IP header fields and functions

(4)

Data Link Protocols

• Key jobs of Data Link layer

– Media Access Control (MAC) – Logical Link Control (LLC)

• Point-to-point data transfer

– Shipping data from one MAC layer address to another

(5)

Guide to TCP/IP, Third Edtion 5

Data Link Protocols (continued)

• WAN encapsulation of frames at Data Link layer involves one or more of the following services

– Addressing

– Bit-level integrity check – Delimitation

– Protocol identification (PID)

(6)

Serial Line Internet Protocol (SLIP)

• Original point-to-point protocol

• Sometimes used to

– Manage communications or networking equipment through a dial-up serial port connection

• Simple packet-framing protocol described in RFC 1055

• Uses a special END character (0xC0)

– Placed at the beginning and end of each IP datagram to delimit, or separate, each payload

(7)

Guide to TCP/IP, Third Edtion 7

Point-to-Point Protocol

• Provides

– Frame delimitation

– Protocol identification and bit-level integrity check services

• RFC 1661 includes

– Encapsulation methods

– A special Link Control Protocol (LCP) – A collection of negotiation protocols

(8)

Point-to-Point Protocol (continued)

• Fields in the PPP header and trailer include

– Flag

– Protocol identifier

– Frame Check Sequence (FCS)

• Supports a default MTU of 1,500 bytes

– Which makes it ideal for interconnecting Ethernet- based networks (or peers)

(9)

Guide to TCP/IP, Third Edtion 9

Special Handling for PPP Links

• For switched technologies

– Bidirectional connections must be negotiated between peers that wish to exchange data

• X.25: RFC 1356. X.25

– Standard set of protocols defined in the 1970s by the International Telecommunications Union (ITU)

• Frame relay: RFC 2427

– Assumes that digital-quality transmission lines are available for creating WAN links

(10)

Special Handling for PPP Links (continued)

• ATM: RFCs 1577 and 1626

– High-speed, long-haul, broadband, cell-switched networking technology

– Offers astonishing and ever-increasing bandwidth

• PPPoE: RFC 2516

– Protocol used by Internet service providers to authenticate and manage broadband subscribers

(11)

Guide to TCP/IP, Third Edtion 11

Frame Types

• At Data Link layer

– Protocol data units are called frames

• Frame

– Represents same data that appears in digital form at the Network layer in an IP datagram

(12)

Ethernet Frame Types

• Ethernet II frame type

– De facto standard frame type used for IP datagram transmissions over Ethernet networks

– Has protocol identification field

• Ethernet frame types that TCP/IP can use

– Ethernet II

– Ethernet 802.2 Logical Link Control

– Ethernet 802.2 Sub-Network Access Protocol (SNAP)

(13)

Guide to TCP/IP, Third Edtion 13

Ethernet II Frame Structure

• Ethernet II frame type fields and structure

– Preamble

– Destination Address Field – Source Address Field

– Type Field – Data Field

– Frame Check Sequence Field

(14)

Ethernet II Frame Structure

(continued)

(15)

Guide to TCP/IP, Third Edtion 15

Ethernet II Frame Structure

(continued)

(16)

Ethernet 802.2 LLC Frame Structure

• Unique fields

– Preamble

– Start Frame Delimiter Field:

– Length Field

– Destination Service Access Point (DSAP) Field:

– Source Service Access Point (SSAP) Field:

– Control Field

– Destination Address – Source Address

– Data

– Frame Check Sequence

(17)

Guide to TCP/IP, Third Edtion 17

Ethernet 802.2 LLC Frame Structure

(continued)

(18)

Ethernet 802.2 LLC Frame Structure

(continued)

(19)

Guide to TCP/IP, Third Edtion 19

Ethernet SNAP Frame Structure

• Fields

– Organization Code Field – Ether Type Field

– Preamble

– Start Frame Delimiter – Destination Address – Source Address

– Length

– Destination Service Access Point – Source Service Access Point

(20)

Ethernet SNAP Frame Structure

(continued)

(21)

Guide to TCP/IP, Third Edtion 21

Token Ring Frame Types

• IEEE 802.5 standard

– Defines token ring networking

• Token ring networks

– Rely on a physical star design, although they use a logical ring transmission path

• On a token ring network

– Each token ring workstation acts as a repeater

• Variations of token ring frames

– Token Ring 802.2 LLC frames – Token Ring SNAP frames

(22)

Token Ring Frame Types (continued)

(23)

Guide to TCP/IP, Third Edtion 23

Hardware Addresses in the IP Environment

• IP addresses

– Identify individual IP hosts on a TCP/IP internetwork

• TCP/IP networking uses ARP to

– Determine the hardware address of the local target for the packet

• ARP cache

– Table of hardware addresses learned through the ARP process

(24)

Hardware Addresses in the IP

Environment (continued)

(25)

Guide to TCP/IP, Third Edtion 25

Hardware Addresses in the IP

Environment (continued)

(26)

Hardware Addresses in the IP

Environment (continued)

(27)

Guide to TCP/IP, Third Edtion 27

ARP Packet Fields and Functions

• Basic ARP packets

– Broadcast ARP request packet

– Directed, or unicast, ARP reply packet

• Most confusing part of ARP

– Interpretation of the sender and target address information

(28)

ARP Packet Fields and Functions

(continued)

(29)

Guide to TCP/IP, Third Edtion 29

ARP Packet Fields and Functions

(continued)

(30)

ARP Cache

• ARP information

– Kept in an ARP cache in memory on most operating systems

• Windows-based systems

– Command arp -a is used to view the table contents – Have utility to view IP and hardware addresses

(31)

Guide to TCP/IP, Third Edtion 31

ARP Cache (continued)

(32)

Proxy ARP

• Method that allows IP host to use a simplified subnetting design

• Enables a router to “ARP” in response to an IP host’s ARP broadcasts

• Most network configurations

– May never need to use proxy ARP

(33)

Guide to TCP/IP, Third Edtion 33

Proxy ARP (continued)

(34)

Reverse ARP

• Used to obtain an IP address for an associated data link address

• Initially defined to

– Enable diskless workstations to find their own IP addresses upon booting or startup

• BOOTP, and eventually DHCP, replaced RARP

(35)

Guide to TCP/IP, Third Edtion 35

About Internet Protocol

• Network layer communications

– End-to-end communications

• Internet Protocol

– Network layer protocol used in the TCP/IP suite

• IP version 4 (IPv4)

– Widely implemented

• Internet Protocol version 6 (IPv6)

– Most used in pilot or experimental implementations

(36)

Sending IP Datagrams

• Requirements for building an IP datagram packet to transmit on the wire

– IP addresses of the source and destination

– Hardware address of the source and next-hop router

• IP host

– Can use a manually entered destination IP address or the DNS to obtain a destination’s IP address

(37)

Guide to TCP/IP, Third Edtion 37

Route Resolution Process

• E

nables IP host to determine if desired destination is local or remote

• Local or Remote Destination?

– Upon determination of IP address

• IP host compares network portion of destination address to its own local network address

(38)

Route Resolution Process (continued)

(39)

Guide to TCP/IP, Third Edtion 39

If Remote, Which Router?

• Types of route table entries

– Host route entry

– Network route entry

• Receiving gateway typically does one of the following

– Forwards packet

– Sends an ICMP reply

– Sends an ICMP reply indicating that it is unclear where to send the packet

(40)

Lifetime of an IP Datagram

• IP packets

– Have a pre-defined lifetime indicated in each packet’s Time to Live (TTL) field

• 64

– Recommended starting TTL value

• 128

– Default TTL in Windows 2000, Windows 2003, and Windows XP

(41)

Guide to TCP/IP, Third Edtion 41

Lifetime of an IP Datagram (continued)

(42)

Fragmentation and Reassembly

• IP fragmentation

– Enables a larger packet to be automatically fragmented by a router

• Once fragmented

– No reassembly occurs until fragments arrive at destination

– All fragments are given the same TTL value

(43)

Guide to TCP/IP, Third Edtion 43

Service Delivery Options

• Precedence

– Used by routers to determine what packet to send

• Type of Service

– Used to select routing path when multiple paths exist – Routing protocols

• OSPF and Border Gateway Protocol (BGP)

(44)

Differentiated Services and Explicit Congestion Notification

• RFC 2474, RFC 2475, and RFC 3168

– Offer a new use of the TOS field bits

– Suggest that TOS and Precedence field bytes be replaced by a Differentiated Services Code Point (DSCP) field

• Diffserv

– Uses DSCP value to enable routers to offer varying levels of service to traffic based on marker placed in the DSCP field

(45)

Guide to TCP/IP, Third Edtion 45

IP Header Fields And Functions

• Version Field

– First field in IP header

• Header Length Field

– Denotes the length of the IP header only

• Type of Service Field

– Has two components: precedence and Type of Service

• Total Length Field

– Defines length of the IP header and any valid data

(46)

IP Header Fields And Functions

(continued)

(47)

Guide to TCP/IP, Third Edtion 47

IP Header Fields And Functions (continued)

• Identification Field

– Each packet is given a unique ID value when sent

• Flags Field

– Three bits long

– Typically, fragmentation is allowed

• Fragment Offset Field

– Shows where to place packet’s data when fragments are reassembled

(48)

IP Header Fields And Functions (continued)

• Time to Live (TTL) Field

– Denotes the remaining lifetime of the packet

• Protocol Field

– Indicates what is coming up next

• Header Checksum Field

– Provides error detection on the contents of the IP header only

• Source Address Field

– The IP address of the IP host that sent the packet

(49)

Guide to TCP/IP, Third Edtion 49

IP Header Fields And Functions (continued)

• Destination Address Field

– Can include a unicast, multicast, or broadcast address

– Final destination of the packet

• Options Fields

– Exist primarily to provide additional IP routing controls

– Can be useful when testing or debugging code or specific connections

(50)

Summary

• Data link protocols

– Manage transfer of datagrams across the network

• At Data Link layer

– Protocols must deliver services, such as delimitation, bit-level integrity checks, addressing, and protocol identification

• Ethernet II frames

– Most common frame type on LANs

(51)

Guide to TCP/IP, Third Edtion 51

Summary (continued)

• Understanding frame layouts

– Crucial for proper handling of contents

• At the lowest level of detail

– Important to understand the differences in field layouts and meanings

• Imperative to understand how TCP/IP manages the translation between MAC layer addresses and

numeric IP addresses

(52)

Summary (continued)

• Proxy ARP

– Permits router to interconnect multiple network segments

• Network layer protocols

– Make their way into the Data Link layer through a process known as data encapsulation

• Important characteristics of IP datagrams

– Time to Live (TTL) values

– Fragmentation of incoming frames – Service delivery options

References

Related documents

If the TCP/IP protocol was previously installed, a network connection icon with the title TCP/IP -> CATC USB/Ethernet Link should also be visible.. To specify the

The transport layer controls the reliability of a cancer link through flow position, which opens the connection, each device uses SMTP to forward messages on trial next host

a) All equipment and piping shall be provided with high point vents and low point drains within isolation valves isolating equipment or process sections. All such vents and

Knows that uses of udp protocols like packet corresponds to the data packets arriving out new icmp message is used by gathering data to help of wpa that use.. Username to work

 TCP/IP four layers: applications, transport, Internet and Network Access. Next, we will look in detail how IP datagram moves through a network when data

Fiocchi offers the ammunition you need for practically any self defense application: for training and practice, our Shooting Dynamics line of pistol and revolver

• Understand the nature of IP address limitations, and how techniques like Classless Inter-Domain Routing and Network Address Translation ease those limitations...

Communication Protocol: COMMUNICATION PROTOCOL Cardtronics TCP/IP Columbus Data TCP/IP Wireless Data Stream (ASAI) TCP/IP Wireless DNS (MoneyTree) TCP/IP Wireless EFX TCP/IP