Introduction to Networking ITT Version - YPW · Generic View of Converting from Binary IP Address to DDN Format. ... IPv4 address that begin with first octet between 0 and 127 Example

NT1210

Final Exam Review 8 to 10

Introducing the Internet Protocol (IP)

TCP/IP Model review: Layers 1 and 2 Protocols

Figure 8-1 Example LAN/WAN Standards and Types in the TCP/IP Model 2


TCP/IP Model review: Upper layers define non-physical (logical) networking functions

Figure 8-2 Various Perspectives on the TCP/IP Model and Roles 3


Network Layer protocols IP: Most important protocol defined by Network layer

Almost every computing device on planet communicates, and most use IP to do so

Network layer also defines other protocols

4

Introducing the Internet Protocol (IP) Network Layer protocols: Part 1

Table 8-1 Other TCP/IP Network Layer Protocols

Name Full Name Comments

ICMP Internetwork Control Message Protocol

Messages that hosts and routers use to manage and control packet forwarding process; used by ping command

ARP Address Resolution Protocol

Used by LAN hosts to dynamically learn another LAN host’s MAC address

DHCP Dynamic Host Configuration Protocol

Used by host to dynamically learn IP address (and other information) it can use

DNS Domain Name System/Service

Allows hosts to use names instead of IP address; needs DNS server to translate name into corresponding IP address (required by IP routing process)

5

Introducing the Internet Protocol (IP) Network Layer protocols: Part 2

Table 8-1 Other TCP/IP Network Layer Protocols

Name Full Name Comments

RIP Routing Information Protocol

Application that runs on routers so that routers dynamically learn IP routing tables (used to route IP packets correctly); open standard protocol defined in RFC 2453

EIGRP Enhanced Interior Gateway Routing Protocol

Proprietary routing protocol owned by Cisco Systems

OSPF Open Shortest Path First

Open source routing protocol defined in RFC 2328

6


IPv6: Next generation of IP addressing.

Needed because IPv4 addresses exhausted.

128-bit long addresses: 2128 or 3.4x1038 or over 340 undecillion IPs, that’s 340 with 36 zero’s after it.

Customer usually gets /64 subnet, which yields 4 billion times IPs available in all of IPv4.

Comparison: Number of IPv4 addresses equal to weight of cat; number of IPv6 addresses equal to weight of Earth and provides enough IP addresses for every grain of sand on every beach on earth.

7


Migration to IPv6 has taken over decade and still in process.

IPv6 originally defined back in mid-1990s.

June 6, 2012 – Was the scheduled IPv6 Day, official worldwide “switch over” day, moved up to February 2012.

Figure 8-3 IPv4 Vs. IPv6 Timeline 8


IP defines many functions that work together with one ultimate goal: To send data from one host to another host through any TCP/IP network.

Most important functions include: Creating end-to-end physical paths through TCP/IP network by

interconnecting physical networks (LANs and WANs) using routers

Identifying individual hosts and groups of hosts using IP addressing

Routing (forwarding) IP packets to correct destination host

Figure 8-4 Example of a Post Office Sorting a Letter Sent to Hollywood, California 9


IP is like Post Office

Figure 8-4 Example of a Post Office Sorting a Letter Sent to Hollywood, California 10


Routers in IP network: Interconnect LANs and WANs via physical connectors called interfaces Example: Cisco 1841 router with two built-in Gigabit Ethernet

LAN interfaces that use RJ-45 connectors

Figure 8-5 Enterprise Class Router, LAN Interfaces, and WAN Interfaces 11


IP interconnects LANs and WANs

Figure 8-7 Interconnected LANs and WANs: Redundancy, but No LAN/WAN Detail 12


IPv4 Addresses 32 bits Expressed in binary and dotted decimal forms Source and destination IP addresses included in 20-byte IP

header added to all IP packets

Figure 8-8 IPv4 Header Format and Fields 13


Converting binary IP address to dotted decimal 1. Separate 32 bits into 4 groups of 8 bits each

2. Do binary-to-decimal conversion of each 8-bit number (each decimal value between 0 and 255)

3. Put period (dot) between each decimal number

Figure 8-9 Generic View of Converting from Binary IP Address to DDN Format 14


Example: Converting binary IP address to dotted decimal

Figure 8-10 Converting Binary IP Address to DDN 10.1.2.3 15

Introducing the Internet Protocol (IP): Routing Routing IP Packets from Source to Destination IP addressing groups addresses into networks

All addresses with same value in first parts of addresses considered to be in one network

Example: All addresses that begin with 11, 12, 13, 14, or 15 in that particular network

Figure 8-11 Example IP Address Groupings: All with the Same First Octet in the Same Group 16

Introducing the Internet Protocol (IP): Routing IP routing example with routing tables: PC11 in left LAN

sends IP packet to address 12.1.1.21 (LAN on upper right)

Figure 8-12 Example IP Address Groupings: All with the Same First Octet in the Same Group 17

Introducing the Internet Protocol (IP): Routing Routers build routing tables in two ways Static configuration: Routes entered manually and do not

change

Dynamic routing protocol: Application router uses to automatically learn new routes from other routers

Figure 8-13 Routing Protocols Advertising All Addresses that Begin with 12 as One Route 18

Introducing the Internet Protocol (IP): Other Protocols Domain Name System/Service (DNS): Mapping

names to IP addresses Users use names; IP

routing uses numbers

DNS translates name into corresponding IP address

DNS client sends DNS Request message

DNS server returns DNS Reply

Figure 8-14 DNS Name Resolution Request, Reply, and Packet to Server1 IP Address 19

Introducing the Internet Protocol (IP): Other Protocols

Figure 8-15 IP with its Support Protocols 20

Layer 3 - Network

IP Addressing on User LANs: Network Settings Locations Need IP addresses Each LAN and WAN interface on hosts and routers need IP

address to communicate

Figure 8-17 IP Addresses Used on Every LAN/WAN Interface 21

IP Addressing on User LANs: Network Settings IP Address grouping: Allows IP routing to work better

Routers list one number to represent each network (address group) in routing tables

Figure 8-18 IP Address Groupings: IP Networks 22

IP Addressing on User LANs: Network Settings Original IPv4 RFC defined way to group IPv4 addresses

using IP address classes (classful IP addressing) Every possible IPv4 address falls into class

Table 8-2 Summary of IPv4 Address Classes Based on First Octet Values 23

First Octet Class Purpose 0 A Reserved 1 - 126 A Unicast addresses, in class A networks 127 A Reserved for loopback testing 128 - 191 B Unicast addresses, in class B networks 192 - 223 C Unicast addresses, in class C networks 224 - 239 D Multicast addresses; not used as unicast IP addresses 240 - 255 E Experimental; not used as unicast IP addresses

IP Addressing on User LANs: Network Settings Class A includes lower half of IPv4 address space: All

IPv4 address that begin with first octet between 0 and 127

Table 8-3 Example Class A Networks 24

Network ID Class A IP Network Concept Size (Number of Addresses)

1.0.0.0 All addresses with a first octet equal to 1 > 16,000,000 2.0.0.0 All addresses with a first octet equal to 2 > 16,000,000 3.0.0.0 All addresses with a first octet equal to 3 > 16,000,000 4.0.0.0 All addresses with a first octet equal to 4 > 16,000,000 … Etc…. > 16,000,000 126.0.0.0 All addresses with a first octet equal to 126 > 16,000,000

IP Addressing on User LANs: Network Settings Class B includes ¼ of IPv4 address space with first

octet value from 128 – 191 Includes medium number (216) of medium sized IP

networks for approximately 65,000 hosts per network

Table 8-4 Example Class B Networks 25

Network ID Concept Size (Number of Addresses)

128.1.0.0 All with a first two octets equal to 128.1 > 65,000 128.2.0.0 All with a first two octets equal to 128.2 > 65,000 128.3.0.0 All with a first two octets equal to 128.3 > 65,000 150.48.0.0 All with a first two octets equal to 150.48 > 65,000 180.255.0.0 All with a first two octets equal to 180.255 > 65,000 191.200.0.0 All with a first two octets equal to 191.200 > 65,000

IP Addressing on User LANs: Network Settings Class C includes 1/8th of IPv4 address space with first

octet between 192 and 223 Large number of small IP networks: over 2,000,000 IP

networks, each with 256 IP addresses each

Table 8-5 Example Class C Networks 26


192.1.1.0 All with a first three octets equal to 192.1.1 254 192.1.2.0 All with a first three octets equal to 192.1.2 254 192.1.3.0 All with a first three octets equal to 192.1.3 254 200.200.200.0 All with a first three octets equal to 200.200.200 254 220.255.0.0 All with a first three octets equal to 220.255.0 254 223.1.1.0 All with a first three octets equal to 123.1.1 254

IP Addressing on User LANs: Network Settings LAN IP address classes summary

Figure 8-20 Summary of How Class Rules Break Down the IPv4 Address Space 27

IP Addressing on User LANs: Network Settings Private addresses: Classful IP networks reserved for

enterprises to use in their network designs Can only be used on local LAN; can’t be routed through

WAN (non-routable) Not regulated by agencies such as ARIN or ICANN

28


10.x.x.x Class A Private IP addressing space Over 16,000,000 networks of over 16,000,000 IPs each

172.16.x.x – 172.31.x.x

Class B Private IP addressing space Over 65,000 networks of over >65,000 IPs each

192.168.x.x Class C Private IP addressing space Over 65,000 networks of 256 IPs each

IP Addressing on User LANs: Network Settings Static IP address assignment: Manually configured

Figure 8-21 Static IP Address Assignment on Mac OS X 29

IP Addressing on User LANs: Network Settings Most host OS’s allow static configuration of several

network settings

Figure 8-22 Host IP Settings 30

IP Addressing on User LANs: Network Settings Dynamic Host Configuration Protocol (DHCP)

defines way hosts can lease IP address from DHCP network server so does not have to be configured statically Operates on client-server concept

DHCP protocol defined by set of RFCs

Figure 8-23 Sample Network for DHCP Discussions 31

IP Addressing on User LANs: Network Settings Example: IP address assignment design using both

DHCP and statically assigned addresses

Table 8-6 Address Planning: Some Static, Some DHCP, for Every LAN 32

Location Type Range

Atlanta LAN Static 11.1.1.1 - 11.1.1.254 DHCP 11.1.2.1 - 11.1.2.254

Boston LAN Static 172.20.1.1 - 172.20.1.254 DHCP 172.20.2.1 - 172.20.2.254

San Fran LAN Static 172.30.1.1 - 172.30.1.254 DHCP 172.30.2.1 - 172.30.2.254

IP Addressing on User LANs: Network Settings Once DHCP server exists in network and has been

configured with set of IP addresses to lease, DHCP clients can request IP addresses

Figure 8-24 DHCP Lease Process between a DHCP Client and Server 33

IP Addressing on User LANs: Network Settings User can see results of DHCP process from computer

Figure 8-25 DHCP Client Configuration on Mac OS X 34

IP Addressing on User LANs: Network Settings DHCP example: Crossing networks to access DHCP

server

Figure 8-26 Remote DHCP Client in Boston 35

IP Routing with Focus on Layer 3

IP defines how to route packets across TCP/IP network

Some routing tasks must use logic from lower two layers because Network layer (3) cannot physically send bits Network layer relies on

Layers 1 and 2 logic for this

Figure 8-27 IP Routing Perspective, While Ignoring LAN/WAN Details 36


Router must have IP routing table with useful entries to route IP packets.

Routing table may list multiple routes.

Each IP route identifies network, as well as other information about how to send packets to that network.

Routers look at incoming packet’s destination IP address and compare it to list of network IDs in its routing table to determine where to send packet to destination.

37


Finding a classful network ID based on IP address

Figure 8-28 Five Classful Networks in a Small Corporate Network 38


Each route in routing table lists: Information about how

to match IP packets

Forwarding instructions that tell router where to forward packets to (e.g., next router)

Example: R1’s IP routing table shows five network IDs so it knows routes to all five networks

Figure 8-29 R1 Routing Table with Routes for Five Classful Networks 39


Router compares incoming IP packet’s destination address to information in its routing tables to find best route to destination

Figure 8-30 How Router R1 Uses its IP Routing Table: Match and Forward 40


Figure 8-31 Routing from End-to-End: Multiple Cooperative Routing Decisions 41

IP Routing with Focus on Layer 3: Subnetting Classful IP networks and wasted IP addresses Subnetting: Process of subdividing network to create smaller

groups of consecutive IP addresses

Subnets (subdivided networks): Smaller groups of addresses

Figure 8-32 Numbers of Classful Networks, and Their Sizes 42

IP Routing with Focus on Layer 3: Subnetting Example: Several subnets created by subnetting network

10.0.0.0

Each subnet has subnet/network ID

Figure 8-33 Subdividing (Subnetting) Class A Network 10.0.0.0 43

IP Routing with Focus on Layer 3: Subnetting Example continued: IP addresses and networks

replaced with five subnets of network 10.0.0.0

Figure 8-34 Sample Corporate Network Using Subnets of Network 10.0.0.0 44

IP Routing with Focus on Layer 3: Subnetting Subnet mask: Shows how much of IP address for each

device is in common to all IPs in subnet Example 255.255.255.0 (/24): First three octets (first 24 bits)

must be equal for all subnets in network

PC11 sends packet to PC21 (destination IP address 10.1.2.21)

R1 will have route for PC21’s subnet (network ID 10.1.2.0)

Figure 8-35 Routing Logic with Subnets and Masks 45

IP Routing with Focus on Layer 3: Subnetting Classful networks have default subnet mask based on

each class Class A: 255.0.0.0 (8 bits)

Class B: 255.255.0.0 (16 bits)

Class C: 255.255.255.0 (24 bits)

If subnet mask anything other than default, then subnetting being used

Figure 8-35 Routing Logic with Subnets and Masks 46

IP Routing with Focus on Layer 3: Subnetting How to calculate subnets

1. Determine network class (A, B, or C) 2. Determine EITHER number of hosts needed for each subnet

OR how many subnets needed 3. Determine how many bits needed to provide correct number of

hosts/subnets; last subnet is NOT usable 4. Calculate IPs for each subnet; first IP identifies subnet (Network

ID) and last IP identifies broadcast address 5. Determine subnet mask (total number of bits for network/subnet

ID)

47

IP Routing with Focus on Layer 3: Subnetting Example: Calculating subnets for network 192.168.12.0 Class: C Number of subnets needed: 14 Number of bits needed to supply 14 subnets: 3 Number of bits left to determine number of IPs per subnet: 5

(results in 32 IPs per subnet) Subnet mask: 255.255.255.224 (default 16 bits + 3 more bits for

subnetting = 19 bits)

48

IP Routing with Focus on Layer 3: Subnetting

49

Subnet No. Network ID Host Range IPs Broadcast IP 0 192.16.12.0 192.16.12.1 – 192.16.12.30 192.16.12.31 1 192.16.12.32 192.16.12.33 – 192.16.12.62 192.16.12.63 2 192.16.12.64 192.16.12.65 – 192.16.12.94 192.16.12.95 3 192.16.12.96 192.16.12.97 – 192.16.12.126 192.16.12.127 4 192.16.12.128 192.16.12.129 – 192.16.12.158 192.16.12.159 5 192.16.12.160 192.16.12.161 – 192.16.12.190 192.16.12.191 6 192.16.12.192 192.16.12.161 – 192.16.12.222 192.16.12.223 7 192.16.12.224 192.16.12.225 – 192.16.12.254 192.16.12.255

IP Routing with Focus on Layer 3: Subnetting What happens when PC11 sends IP packet to PC12:

Same subnet 1. PC11 determines its own

IP address and subnet mask (10.1.1.11 and 255.255.255.0)

2. PC11 decides determines destination is in same subnet

3. PC11 sends packet directly to PC12 without going through router R1

Figure 8-36 IP Host Routing Logic: Local Destination 50

IP Routing with Focus on Layer 3: Subnetting What happens when PC11 sends IP packet to PC12:

Different subnets 1. Host’s default gateway (default router) setting tells it where to

send packets when they have destination address in different subnet

2. Default gateway tells host IP address of router attached to its LAN

3. Router then consults its routing table and determines how to deliver packet

Figure 8-37 IP Host Routing Logic: Remote Destination 51

IP Routing with Layer 1, 2, and 3 Interactions Encapsulation: Action taken by lower layer when it

takes data from higher layer and adds header (and sometimes trailer) to higher layer’s data

Example: PC11 opened web browser and tried to connect to URL at web server: PC11 creating bits it uses to send to server S1 (web server)

Figure 8-38 Encapsulation Review: Application, Transport, and Network Layers 52

IP Routing with Layer 1, 2, and 3 Interactions PC encapsulating IP packet into Ethernet frame (step 4)

Sending bits over LAN cable into network (step 5)

Figure 8-39 Encapsulation Review: Data Link Layer 53

IP Routing with Layer 1, 2, and 3 Interactions De-encapsulation: On the destination side

Figure 8-40 De-encapsulation on a Receiving Host (S1) 54

IP Routing with Layer 1, 2, and 3 Interactions Addressing frames and packets when crossing SAME

subnet: Both MAC and IP addresses in Ethernet frame and encapsulated IP packet

Figure 8-42 IP and Ethernet Addresses, PC11 to server S1, Same Subnet 55

IP Routing with Layer 1, 2, and 3 Interactions To learn destination MAC address, sending device uses

Address Resolution Protocol (ARP) and info in ARP table

Table 8-9 How a Sending IP Host Knows What Addresses to Use

Address Short Answer Long Answer

Source MAC On NIC Given to Ethernet NIC by manufacturer; sending host can find MAC on NIC hardware.

Source IP Configuration Either through static configuration or DHCP

Destination MAC ARP

From its ARP table, or if not found, by using ARP protocol and sending ARP Request and waiting for ARP Reply from destination

Destination IP User Either typed or clicked by user

56

IP Routing with Layer 1, 2, and 3 Interactions Discovering MAC addresses using ARP: ARP Request

and ARP Reply ARP Request (ARP

Broadcast): Sending device queries for MAC address of destination device; sends Request as broadcast to all other devices on subnet

Example: PC11 wants to send packet to server S1 (in same subnet) but does not know S1’s MAC address; PC11 sends ARP Request to all devices on subnet

Figure 8-43 ARP Request (Broadcast) 57

IP Routing with Layer 1, 2, and 3 Interactions ARP Reply: Lists IP address ARP Request asked about

with corresponding MAC address of that host Example: ARP Reply that server

S1 makes in response to PC11’s ARP Request

ARP Reply is unicast since ARP Request generated from one particular device

Figure 8-44 ARP Reply (Unicast) 58

IP Routing with Layer 1, 2, and 3 Interactions Routing data between different subnets IP packets in network act like person traveling to destination,

using all forms of transportation; packet goes from end-to-end

Data Link frames act like individual vehicles used for only part of trip (e.g., just train); frames never leave their own LAN/WAN

Figure 8-45 Example, IP Packet End-to-End, Data Link Heads Stay on LAN or WAN 59

IP Routing with Layer 1, 2, and 3 Interactions Addressing frames and packets when crossing subnets

example: PC11 (10.1.1.11) sends IP packet to PC21 (10.1.2.21) Hosts sit on different LANs (may also be in different subnets)

Figure 8-46 IP Addresses Stay the Same Through End-to-End Path 60

IP Routing with Layer 1, 2, and 3 Interactions Example: PC11 sends IP packet to PC21 PC11’s logic tells it to send packet to default router because

destination is in different network or subnet

PC11 encapsulates packet inside Ethernet frame with destination MAC address R1

Figure 8-47 Ethernet Frames Use MAC on that LAN (Only) 61

IP Routing with Layer 1, 2, and 3 Interactions Removing/adding Data Link headers: Router removes

IP packet from incoming Data Link frame (de-encapsulation) and then adds new Data Link header and trailer before sending packet (encapsulation)

Steps router goes through: 1. De-encapsulates IP packet from inside Data Link frame 2. Makes routing decision using packet’s destination IP address

and its own IP routing table, identifying correct outgoing interface

3. Encapsulates packet into new Data Link frame that works on outgoing interface

4. Sends packet through outgoing interface to destination

Figure 8-48 Routers Discard Old and Add New Data Link Framing 62

IP Routing with Layer 1, 2, and 3 Interactions Example: When R1 receives packet destined to subnet

on R2

Figure 8-48 Routers Discard Old and Add New Data Link Framing 63

IP Routing with Layer 1, 2, and 3 Interactions Using ARP with routers: R2 needs to deliver IP packet

to host PC21 1. R2 builds Ethernet header with

PC21’s MAC address as destination

2. If R2 does not know PC21’s MAC address (i.e., it is not in its ARP table), R2 uses ARP to learn MAC address

3. When R2 receives ARP Reply with PC21’s MAC address, sends frame

Figure 8-49 Example of Router R2 Using ARP to Learn a Local Host’s MAC Address 64

The Internet as a Network of Networks

Figure 9-1 Internet Access Links from TCP/IP Networks, Large and Small 65


Internet Service Providers (ISPs) create Internet core

Creates physical network for IP packets to travel between enterprises and individual users

Figure 9-2 The Internet Core, with Multiple Service Providers 66


Connecting enterprises

Figure 9-3 Typical Organizations Whose TCP/IP Networks Connect to the Internet 67


Connecting to Internet edge: Part of Internet topology between ISP and customer (sits at edge of both networks)

Figure 9-4 Comparing an Enterprise and ISP Network 68


From network layer perspective: Internet access link acts like any other WAN link between routers

Figure 9-5 T3 Serial Link Connection to the Internet 69


Securing Internet edge: Enterprises use many security measures and devices to make Internet connection more secure Firewalls Intrusion Prevention Systems (IPS)

Example: Firewall sits in path that all packets take; IPS sits outside path so LAN switch forwards packets to IPS and it analyzes packets and watches for signs of problems

Figure 9-6 An Example Case of Using an Enterprise Firewall and IPS 70


Typical rules for enterprise firewall A. (Default): Allow inside clients to reach outside

servers in Internet

B. (Default): Disallow outside clients from sending packets to inside servers, unless another rule allows packet

C. (New Rule): Allow outside clients to connect to the two public web servers in DMZ

Example: Two attempts from users in Internet to connect to two different servers in enterprise Figure 9-7 Firewall Allowing Connections to Public Web Servers Only

71


Each WAN technology creates connection between user’s device and ISP

WAN connection might connect user’s device directly to WAN or may use router (not shown in example)

Figure 9-8 Four Main Options for Individual Internet Access 72


Connecting Customers to ISP Point-of-Presence (PoP): Each ISP has to create connections Connections between ISP’s customers

and ISP PoP Connections between all ISP’s PoPs

create ISP’s own network and allow all of customers to send packets to one another

Connections to other ISP networks form Internet core which allows all Internet hosts everywhere to send packets to each other

To create effective Internet access service, ISP needs number of PoPs in different locations

Figure 9-9 ISP Point-of-Presence (PoP) Concept with Customer Access 73


Example: Typical PoP with access routes using direct link to distribution router which connects to rest of ISP’s network

Figure 9-10 Example of Dividing Responsibilities Inside an ISP PoP 74


Connecting PoPs to create ISP network example ISP might put two more routers at centralized site and use 10-

Gbps Ethernet or SONET equivalent (called OC-192) on all links (center of graphic)

Figure 9-11 Connecting All ISP PoP Routers to Create an ISP TCP/IP Network 75


ISPs work together to create Internet core

Internet core connects all ISPs to all other ISPs (sometimes directly; sometimes indirectly)

Result: All ISPs can send packets to hosts connected to every other ISP

Figure 9-12 Creating the Internet Core: Connections Between Large ISPs 76


Tier 2 ISPs rely on connections to Tier 1 ISPs for some of their connections to Internet

Tier 2 ISPs connect to one or more Tier 1 ISPs rather than connecting to ALL Tier 1 ISPs across globe

Figure 9-13 Connectivity Between Tier 1 and Tier 2 ISPs 77


Other providers of Internet services: Companies who provide services available through Internet Web hosting Search engines Social media Cloud services

Figure 9-14 Other Service Providers Connected to the Internet 78


Other providers of Internet services Web Hosting: Customer picks URL for its website, creates

content for website, and puts website files onto servers that sit at web hosting company

Search Engine: Computers inside service provider’s network have programs that act like web browsers, systematically getting copy of every web page they can find on Internet

Social Media: Service provider that builds web servers that provide framework for users to add their own content (text, photos, video, apps)

Cloud Services: Large variety of services available through Internet

79


Web hosting example: Company website (www.example.com) exists on servers owned by web hosting company

When user browses to www.example.com, packets flow to/from servers at web hosting company

Figure 9-15 Hosting a Web Site at a Web Hosting Service, Not in the Enterprise’s IP Network 80

Internet Access Technologies

Phone line and analog modem (Layers 1 and 2) Internet access: When customer calls, Telco passes call to ISP PoP over phone line not being used at moment

Example: Two ISP customers with analog modems If ISP wants to support many concurrent users in PoP, they

need many modems Once dialed in, users’ PCs can send and receive bits with

ISP through R1

Figure 9-16 Two ISP Customers Using Analog Modems and Analog Phone Lines 81


PPP and DHCP: Together they help customer’s PC learn its public IP address, subnet mask, default gateway, and IP addresses of DNS servers so PCs can access Internet

Figure 9-17 Role of PPP on a Analog Dial-up Circuit to an ISP 82


Using analog phone lines for Internet access Analog modems use symmetric speeds: Upstream speed (from

customer to ISP) same as downstream speed (from Internet to customer)

For most Internet applications, more bytes flow downstream than upstream

Asymmetric service with faster downstream speeds actually works better

83


Using analog phone lines for Internet access

Table 9-1 Comparison Points: Analog Modem 84

Name Analog Modem Physical link Telco local loop Always on? No Allows voice at same time over same medium? No Asymmetric? (Faster downlink possible?) No Approximate real-life downlink speeds 56 Kbps


Digital technologies from Telcos: Integrated Services Digital Network (ISDN) and Digital Subscriber Line (DSL) DSL requires changes to devices at end of local loop cabling,

including device in Telco CO Traditional CO voice

switch does not know what to do with DSL higher frequencies, so CO needs DSL Access Multiplexer (DSLAM) for DSL frequencies

Figure 9-18 DSL Using Multiple Frequencies over a Single Local Loop 85


Line splitter allows both analog phone and DSL modem to connect to same phone line and transmit simultaneously

Figure 9-19 Home Cabling and Devices for DSL 86


DSLAM uses Frequency Division Multiplexing (FDM) to separate voice and data frequencies in same electrical signal

DSLAM does not process data or voice; just passes data or voice off to correct device (router or traditional voice switch)

Figure 9-20 DSLAM Multiplexes Voice to the PSTN and Data to the ISP 87


DSL uses Data Link protocol PPP (Point-to-Point Protocol) to move data (IP packet encapsulated in PPP frame) to DSLAM which then moves PPP frame to ISP router

Figure 9-21 PPP Encapsulated IP Packets Going from Home to ISP Router over DSL 88


Differences and similarities between analog and DSL modems

Table 9-2 Internet Access Link Comparison Points: Analog and DSL 89

Name Analog Circuit DSL

Physical link Telco local loop Telco local loop

Always on? No Yes Allows voice at same time over same medium?

No Yes

Asymmetric? (Faster downlink possible?)

No Yes

Approximate real-life downlink speeds 56 Kbps 24 Mbps


Cable TV and cable modem: Cable modem uses different frequency channels than those used for video (TV) Cable Internet

service just like another TV channel

Instead of video, channel sends data

Figure 9-22 Cable Internet Using Multiple Frequencies over a Single Circuit on Co-axial Cable 90


Cable modem example: Cable modem feed comes from same cable as TV connection

Figure 9-23 Home Cabling and Devices for Cable Internet 91


Fiber to the Neighborhood (FTTN): Fiber goes to front of neighborhood with coaxial rest of way to houses

Fiber to the Curb (FTTC): Fiber goes into neighborhood and is buried at curb (closer to homes)

Figure 9-24 Hybrid Fiber Coax (HFC) and Fiber-to-the-Curb (FTTC) 92


Head End: CATV (cable access TV) company’s equivalent of Telco’s Central Office (CO) Has space to hold various devices, including those that

connect to ends of HFC cables

Figure 9-25 CMTS and Head End Multiplexes Video and Data 93


Differences and similarities between cable Internet, DSL, analog modems

Table 9-3 Internet Access Link Comparison Points 94

Name Analog Circuit DSL Cable Physical link Telco local loop Telco local loop CATV cable Always on? No Yes Yes Allows voice at same time over same medium?

No Yes Yes

Asymmetric? (Faster downlink possible?)

No Yes Yes

Approximate real-life downlink speeds

56 Kbps 24 Mbps 50 Mbps


Wireless Telco and 4G: Wireless WAN technology supports many devices (mobile phones, tablets, laptops or other computers)

Devices can have built-in wireless WAN card or can use wireless WAN expansion card

Figure 9-26 Wireless WAN Examples 95


Consumer Internet-access technologies use cabling already in most homes; makes it inexpensive and affordable

Figure 9-27 Enterprise WAN Options Used as Internet Access Technologies 96

Network Layer Concepts Before Scarce IP Addresses Individual IP addresses must be unique to each host

connected to Internet before they can send or receive IP packets

Hosts use IP addresses based on class A, B, or C networks

Addresses can not be assigned randomly

Organized IP addresses helps routers to build usable routing tables of networks Makes routing tables shorter and routing more efficient

97

Network Layer Concepts Before Scarce IP Addresses Many different organizations (typically part of some not-

for-profit organization) work together to assign IP addresses for Internet worldwide IANA: Part of ICANN (Internet Corporation for Assigned Names

and Numbers) works with five worldwide regional organizations to manage address assignment process

Table 9-4 Regional Internet Registries (RIRs) 98

Name Locations Served AfriNIC Africa APNIC Asia Pacific ARIN North America LACNIC Latin America, Caribbean RIPE NCC Europe, Middle East, Central Asia

Network Layer Concepts Before Scarce IP Addresses Early days of Internet: Original rule for assigning

addresses was for each company to use one classful IP network for its network When company wanted to

connect to Internet, it applied to IANA for classful network

IANA reviewed application and assigned network ID

Figure 9-29 IANA Assigned Classful IP Network Numbers 99

Network Layer Concepts Before Scarce IP Addresses IANA IP network assignments followed these general

rules: 1. Only assign network IDs not yet

assigned to any other enterprise 2. Assign class of network just large

enough to meet need of enterprise

At end of process, each enterprise had public address that fell into class A, B, or C IP address from public network

could be used to send packets to any other network in Internet

Figure 9-30 Enterprises Subnet their One Classful IP Network 100

Network Layer Concepts Before Scarce IP Addresses Example of SOHO address assignment in early days:

ISP1 reserved class C network 200.2.2.0 When PC2 and PC3 connect to ISP, they are given addresses

by ISP1 router

Figure 9-31 Assigning IP Addresses to SOHO PCs 101

Network Layer Concepts Before Scarce IP Addresses Border Gateway Protocol (BGP): Internet IP routing

protocol Prefers routes through less

expensive links

Creates large routing tables

Figure 9-32 BGP: Choosing Routes (Indirectly) Based on Business Rules 102

Network Layer Concepts Before Scarce IP Addresses In Internet core, routing tables have grown to over

400,000 routes

So BGP built to be better able to handle larger numbers of routes

Figure 9-33 Scale of Internet Routing Tables: Large Enterprise Vs. Internet Core Routers 103

Network Layer Concepts Before Scarce IP Addresses Once classful network

has been assigned to company, all routers in Internet core need to know how to forward packets so they can reach ISP connected to company

Figure 9-34 Internet Routing: IP Routes to Each Classful IP Network 104

Network Layer Concepts Before Scarce IP Addresses Routers receive packets and then send them to next

router

Figure 9-35 IP Forwarding (Routing) on Several ISP Routers 105

Network Layer Concepts Before Scarce IP Addresses Single-homed connection means that enterprise has

only one WAN link connecting to ISP

Figure 9-36 Single-Homed Connection with Default Route 106

Network Layer Concepts Before Scarce IP Addresses Dual-homed Internet connection means enterprise has

two (or more) connections to Internet

Gives enterprise choice of where to send Internet packets

Default route might not work well in such network designs

Figure 9-37 Inefficient Routes With Dual-homed Internet Connections 107

Network Layer Concepts Before Scarce IP Addresses Dual-homed example: Enterprise uses BGP between

itself and both ISP1 and ISP2

ISP2’s router would advertise routes for networks 22.0.0.0 and 23.0.0.0, and routers R1 and R2 view route to Internet through ISP2 as better route

Figure 9-38 Partial BGP Updates 108

Network Layer Concepts Before Scarce IP Addresses Example: User device connects to Internet without

using router Host has OS that includes TCP/IP software

IP software includes concept of default router

When connected to Internet, host’s default router setting refers to ISP router

Figure 9-39 Default Routers and Default Routes 109

Network Layer Concepts Before Scarce IP Addresses Name resolution and Global DNS system: Creating

globally unique hostnames

DNS names assigned by IANA

Process for how companies and individuals get and use hostnames in Internet similar to assigning IP addresses

Figure 9-40 Review: IANA Assigns IP Networks 110

Network Layer Concepts Before Scarce IP Addresses To create globally unique hostnames, process relies on

domain names

With this format, names exist as characters with periods in between

Subdomain: Last part of name

Figure 9-41 Format and Examples Using Domain Names 111

Network Layer Concepts Before Scarce IP Addresses To ensure unique hostnames throughout Internet,

company or individual must register subdomains with IANA-authorized company

If requested name not already in use, agency registers name so no other entity can use it

Figure 9-42 IANA/Others Approve Subdomain Registrations 112

Network Layer Concepts Before Scarce IP Addresses Hostnames on LANs follow domain name format, too

Administrative process ensures no two hostnames will ever be same

Enterprises must not duplicate names inside company

Figure 9-43 IANA/Others Approve Subdomain Registrations 113

Network Layer Concepts Before Scarce IP Addresses Example: Name server for companies Ent-1, Ent-2, and

Ent-3 In each case, name server

lists short version of name, along with IP address used by that host

Name server considers each short name to have correct subdomain at end of name

Figure 9-44 DNS Servers and Distributed Server Configurations 114

Network Layer Concepts Before Scarce IP Addresses DNS defines how world creates distributed database of

hostnames and their addresses DNS server for each subdomain

knows all hostnames and IP addresses for that subdomain

Root DNS servers: Special DNS servers inside Internet know IP addresses of all DNS servers

DNS defines protocol that servers use to ask among all DNS servers to find DNS server for right subdomain

Figure 9-45 Finding the Right DNS Server for a Domain Name in Another Company 115

Network Layer Concepts Before Scarce IP Addresses At this point, client does not yet know www.ent-1.com’s

IP address Step 5: Server 128.1.9.9 sends name

resolution request to DNS for subdomain server ent-1.com

Step 6: DNS server ent-1.com knows name “www.ent-1.com,” so replies with IP address 1.1.1.1

Step 7: DNS server replies to Client A with IP address of 1.1.1.1 so Client can now send packet with correct IP address on it

Figure 9-46 Getting a Response from the Authoritative DNS Server for Ent-1.com 116

Network Layer Concepts with Scarce IPv4 Addresses IPv4 address exhaustion Became clear by late 1980s that world would run out of IPv4

addresses with current IP class plan

Original address assignment plan had problems in part because of sizes of classful IP networks and number of each that existed

Table 9-4 Number and Sizes of Classful IP Networks 117

Class Number of Networks

Size (Number of Host Addresses)

A 126 224 – 2 (>16,000,000) B 16,384 216 – 2 (>65,000) C 2,097,192 28 – 2 (254)

Network Layer Concepts with Scarce IPv4 Addresses Example of IP address assignment: Enterprise asks for

Class B network from IANA IANA grants network

128.1.0.0

Internet routers update routing tables with routes for 128.1.0.0; entire class B network must be in one place

Figure 9-47 Wasted IP Addresses: Got 65,000, Need 500 118

Network Layer Concepts with Scarce IPv4 Addresses Graph: Number of estimated

Internet hosts 1984 – 1992

Data derived primarily from RFC 1296, which collected growth data in part because of IP address exhaustion problem

Figure 9-48 Approximate Number of Hosts Connected to the Internet, 1984 - 1992 119

Network Layer Concepts with Scarce IPv4 Addresses Classless Interdomain Routing (CIDR): One method to

deal with IP address depletion

Used by IANA

Each CIDR block is set of consecutive IP addresses unique in Internet (same as classful IP networks)

Figure 9-49 IANA Assigns to ISP; ISP Assigns Smaller CIDR Block to Customer 120

Network Layer Concepts with Scarce IPv4 Addresses CIDR reduces routing table growth with route

aggregation Example: ISP1 has 3 customers, each of which has CIDR block

of public IP addresses

Router R4 (part of ISP1’s network) has routes for each customer’s CIDR block

Figure 9-50 CIDR Address Assignment Creates Larger Routing Tables 121

Network Layer Concepts with Scarce IPv4 Addresses Route aggregation requires worldwide IP address

assignment process to assign numbers in large, consecutive groups Large group first assigned

to large enterprise such as ISP

Then ISP assigns smaller CIDR blocks to its customers

Administrative process allows routers to create aggregate routes for original large blocks, rather than separate routes for each individual smaller block

Figure 9-51 CIDR Route Aggregation Keeps Other ISP Routing Tables Smaller 122

Network Layer Concepts with Scarce IPv4 Addresses Network Address Translation (NAT): Way to translate

multiple PRIVATE addresses to single PUBLIC address for Internet access

Figure 9-52 Hosts with Public IP Addresses Connected to Servers in the Internet 123

Network Layer Concepts with Scarce IPv4 Addresses Three different connections from one host Server maps IP address for each connection

Figure 9-53 One Client Host with Three Application Connections 124

Network Layer Concepts with Scarce IPv4 Addresses NAT combines connections into one Example: Three real devices each connect to same real web

server Router implementing NAT makes all three connections look like

they come from single host (128.1.1.4)

Figure 9-54 NAT Function on a Router 125

Network Layer Concepts with Scarce IPv4 Addresses Example using private and public IP addresses Three separate enterprises use PRIVATE networks based on

10.0.0.0

Each company uses different PUBLIC IP address block to access Internet

Figure 9-55 Three Enterprises Networks, Each Using Private Network 10.0.0.0 126

Network Layer Concepts with Scarce IPv4 Addresses Public and private IP addresses: RFC 1918 sets aside

several private IP network address blocks

Enterprise can pick private address block, assign IP addresses from that block, subnet that block, etc.

Table 9-5 Private IP Networks 127

Class Number of Networks

Network IDs

A 1 10.0.0.0 B 16 172.16.0.0 - 172.31.0.0

C 256 All that begin 192.168 (192.168.0.0, 192.168.1.0, 192.168.2.0, and so on, through 192.168.255.0)

Network Layer Concepts with Scarce IPv4 Addresses Basic NAT mechanics: NAT translates (changes) IP

addresses inside IP headers as packets pass through device doing NAT Step 1: PC sends

packet to router

Steps 2-3: Router translates private IP to public IP

Step 4: Router sends updated packet to public Internet

Figure 9-56 NAT Translating the Source Address in Packet from Inside to Outside 128

Network Layer Concepts with Scarce IPv4 Addresses NAT example, Part 2: Server replies to host Packet comes into NAT router with IP address of 200.1.1.1

Step 6: Router consults its NAT table to translate packet’s address to Client A’s IP address (10.1.1.1)

Step 7: Router forwards packet to Client A

Figure 9-57 NAT Translating the Destination Address in Packet from Outside to Inside 129

Network Layer Concepts with Scarce IPv4 Addresses Enterprise still needs some public IP addresses so can

access Internet and be accessible by users outside enterprise (e.g., for web services) 1. For NAT devices

2. For hosts in enterprise that need static, public IP addresses (typically servers)

Figure 9-58 Public and Private IP Addresses in the Enterprise 130

Network Layer Concepts with Scarce IPv4 Addresses SOHO address assignment: Most SOHO connections to

Internet use small, consumer-grade routers that typically combine many functions into one device

Figure 9-59 Various Roles of Consumer “Router” 131

Network Layer Concepts with Scarce IPv4 Addresses Router typically has defaults such as Dynamically uses one public IP address (from ISP) on WAN

port Uses that one public IP for NAT Makes WAN port “outside” port for NAT Processes traffic coming in from LAN ports with NAT Picks one private IP network to use on LAN (typically

192.168.1.0) Acts as DHCP server on LAN ports to lease IP addresses to all

hosts on LAN Acts as firewall, allowing Intranet clients to connect to Internet

and preventing Internet clients from getting onto Intranet

Figure 9-59 Various Roles of Consumer “Router” 132

Network Layer Concepts with Scarce IPv4 Addresses Example SOHO address assignment

User can change router defaults or use directly out of box as is

Figure 9-60 Default Settings on a Consumer-Grade Integrated Router 133

Transport and Application Protocols

TCP/IP Transport: TCP/IP model’s two upper layers (Application and Transport) define how applications communicate and other important features of what applications can do on network

Transport and Application Layers focus on hosts

Figure 10-1 Scope of Impact for TCP/IP Layers 134


Host perspectives on upper layers: Upper layer protocols exist in both application and OS

Application developers include Application layer protocol in application (e.g., Telnet)

OS vendor includes Transport protocol inside OS (e.g., IE in Windows)

Figure 10-2 Software Architecture of Application and Transport Layers 135


Serving needs of next higher Layer: On hosts, each function has needs and supplies answer to needs of other functions

Example: Web browser Application needs to get web page;

Application protocol takes care of it using browser application and HTTP does that by using HTTP GET command

Figure 10-3 Needing and Supplying Services in TCP/IP Upper Layers 136


Encapsulation and headers: Application and Transport layer protocols use headers to do their work

Application protocol on sending host adds Application protocol header that destination host’s Application layer protocol reads

Transport layer adds headers based on protocol used: TCP or UDP

137


UDP header format

TCP header format

Figure 10-4,5 UDP/TCP Header Reference 138


Sending host adds original Application and Transport layer header to data to create message; upper layer messages remain mostly unchanged as they pass through network

Example: Message from web server going the web browser; message shows TCP, HTTP, Data Link, and IP headers plus data going through route from host to host

Figure 10-6 Encapsulation with Web Traffic, All Layers 139


Applications and their preferred Transport protocols

Figure 10-8 Some Applications Using TCP, and Some Using UDP 141

Transport Layer Concepts

Elements of Transport Protocols Addressing

Connection Establishment

Connection Release

Flow Control and Buffering

Multiplexing

Crash Recovery



TCP: Reliable, in-order delivery Congestion control

Flow control

Connection setup

UDP: Unreliable, unordered delivery No-frills, “best-effort” delivery

Delay guarantees

Bandwidth guarantees



Connection establishment using three-way handshake CR = CONNECTION REQUEST (a) Normal operation (b) Old CONNECTION REQUEST appearing out of nowhere (c) Duplicate CONNECTION REQUEST and duplicate ACK

144


Connection release (a) Normal case of three-way handshake release

(b) Error case: Final ACK lost

145


Flow control: “Window” can dynamically resize According to network conditions

According to sender’s capacity

According to receiver’s capacity

http://wiki.treck.com/File:Fig1.40_Using_a_Sliding_Window_Protocol.gif 146


Buffering (a) Chained fixed-

size buffers

(b) Chained variable-sized buffers.

(c) One large circular buffer per connection

147


Multiplexing Multiplexing at sender: Handles data from multiple sockets,

adds transport header (later used for demultiplexing) Demultiplexing at receiver: Uses header info to deliver received

segments to correct socket

148


Crash Recovery: Different combinations of client and server strategies

149

Transport Layer Port Numbers

Most host OSs allow multiprocessing which allows more than one program to be active at same time

Each active program gets share of CPU and RAM with all programs taking turns

Transport of data packets similar Protocol

identifies correct application process on destination host and uses port to identify communication session

Figure 10-9 Concept of Application-to-Application Flows Between Two Apps 150


Port numbers identify application processes

Example: 3 TCP communication sessions with TCP port numbers; Both hosts are using TCP port 1024 so have to use different TCP port numbers to identify separate communication sessions

Figure 10-10 Three TCP Flows with Unique TCP Ports per Host 151


Port numbers need to be unique on each source host because of how TCP uses destination port number

Example: Right shows destination host’s TCP software; when top segment arrives (destination port 80), Host2 looks at its list of active TCP ports to find port 80

Figure 10-11 Destination Host Chooses Right Destination Application Based on Destination Port 152


Initializing servers with well known ports example: Two server software processes (web server and email server) Web server uses HTTP (Application protocol) which uses

default port of 80

Email server uses POP3 (Application protocol) which uses port 110

Figure 10-12 Two Servers with Well-Known Ports Open and Listening for New Connections 153


What happens on server when server software registered to use specific port number?

Example using web server: Software uses its default setting to use port for HTTP: TCP port 80

Figure 10-13 Server Initializing Well-Known Port 80 for HTTP 154


Web browser software knows web servers should use port 80 by default

Email client software knows that POP3 servers use TCP port 110 by default

Figure 10-14 Clients Send TCP Segments to Correct Well-Known Port Numbers 155


Table 10-1 Common Application Protocols and Their Well-known Port Numbers

Application Protocol

Transport Protocol

Port Number

Description

HTTP TCP 80 Used by web browsers and web servers Telnet TCP 23 Used for terminal emulation SSH TCP 22 Used for secure terminal emulation FTP TCP 20, 21 Used for file transfer DNS UDP 53 Used for name-to-IP resolution SMTP TCP 25 Used to send Email POP3 TCP 110 Used to receive Email IMAP TCP 143 Used to receive Email SSL TCP 443 Used to encrypt data for secure transactions SNMP UDP 161, 162 Used to manage TCP/IP networks

156


Dynamically allocated port

Figure 10-15 Client Initializing a Dynamic Port Number Assigned by OS (TCP) 157


Dynamic port assignment on client computer when user opens web browser

Figure 10-16 Client Initializing a Dynamic Port Number Assigned by OS (TCP) 158


IANA regulates range of numbers for well known ports, dynamic ports, and registered ports

Ranges apply to both TCP and UDP

Table 10-2 Well-known, Registered, and Dynamic Port Numbers

Type Port Number Range Well-known 0 - 1023 Registered 1,024 – 49,151 Dynamic 49,153 – 65,535

159


To deliver data, TCP encapsulates data inside TCP segment

Segment lists source port and destination port

To begin communication process, servers initialize and start listening for new sessions from clients

Figure 10-17 Email and Web Servers Waiting for Flows 160


Example: Client opens web browser to connect to web server which creates multiple TCP sessions

Client needs three TCP port numbers, one per session

User also checks his email which creates fourth TCP session

Figure 10-18 Four Flows with (Dynamic) Source Ports and Well-Known Destination Ports 161


Four returning messages with their respective port numbers

Figure 10-19 Port Numbers Reversed for TCP Segments in the Opposite Direction 162

Other Transport Functions: Segmentation

Packets restricted for size in TCP/IP network so use segmentation to break large data packages into smaller pieces

Maximum Transmission Unit (MTU): Maximum size of IP packet that can be sent out network device interface (e.g., router) Based on interface’s

Data Link protocol; example: Ethernet has MTU of 1500 bytes for TCP

Figure 10-20 IP MTU Concept on Ethernet Links 163


IP fragmentation and TCP segmentation play important roles in TCP/IP networks TCP on sending host breaks large data “chunks” into smaller

pieces when creating original TCP segments

TCP segmentation example: Web server needs to send web object (picture.jpg) which is 14,600 bytes

File size exactly 10 times MSS on server’s Ethernet interface so divided into 10 segments for transport

Figure 10-21 Web Server Sends Web Object; TCP Segments 164


UDP datagram: UDP messages that include UDP header and its encapsulated data

UDP also needs to segment data: Limited to maximum size of each link

Example: UDP datagram MTU 1472 bytes on Ethernet link

Figure 10-22 UDP Datagram Maximum Data Size on Ethernet Links 165

Other Transport Functions: Connection Management TCP guarantees delivery and has error recovery built in

(connection-oriented)

To confirm destination received data, TCP uses acknowledgments for each segment received with no errors Example: Web server sends three TCP segments to web

browser with sequence numbers (SEQ); client sends message back to server (ACK) stating all three segments received and to send next set of segments

166

Other Transport Functions: Connection Management When using TCP, sender/receiver perform “handshake”

before exchanging data Agree to establish connection (each knowing other willing to

establish connection)

Agree on connection parameters

Figure 10-23 TCP Sequence Numbers and Acknowledgement Concepts 167

Other Transport Functions: Connection Management Three-way handshake

SYNbit=1, Seq=x

choose init seq num, x send TCP SYN msg

ESTAB

SYNbit=1, Seq=y ACKbit=1; ACKnum=x+1

choose init seq num, y send TCP SYNACK msg, acking SYN

ACKbit=1, ACKnum=y+1

received SYNACK(x) indicates server is live; send ACK for SYNACK;

this segment may contain client-to-server data received ACK(y)

indicates client is live

SYNSENT

ESTAB

SYN RCVD

client state LISTEN

server state LISTEN

168

Other Transport Functions: Connection Management Congestion control: Too many sources sending too

much data too fast for network to handle

Different from flow control!

Manifestations Lost packets (buffer overflow at routers)

Long delays (queuing in router buffers)

169

Other Transport Functions: Connection Management UDP: Connectionless protocol Does not use acknowledgements

Does not use sequencing

Will not retransmit missing datagrams

Considered less reliable than TCP

Has much less overhead than TCP

Much faster than TCP

170

Other Transport Functions: Error Recovery

TCP error recovery uses SEQ and ACK packets 1. Data sent from source in TCP segments with sequence numbers

2. Source expects to receive ACK from destination with next sequence number

3. If source does not receive ACK with expected value or receives no ACK at all in reasonable time, retransmits TCP segments

171

Other Transport Functions: Error Recovery

When receiving host gets some, but not all segments, can send back ACK but with value that tells sender to retransmit some data

Example: Second TCP segment has bit errors that occurred during its trip through network so destination router discards TCP segment

Figure 10-24 An Example with an Error; the Recovery Happens Later 172

Comparing TCP and UDP

TCP RFCs: 793,1122,1323, 2018, 2581 Point-to-point: One sender, one receiver Reliable, in-order byte steam: No “message boundaries” Pipelined: TCP congestion and flow control set window size

Full duplex data Bi-directional data flow in same connection MSS: Maximum segment size

Connection-oriented: Uses handshaking Flow controlled: Sender will not overwhelm receiver

173


UDP does NOT guaranteed delivery (connectionless) so Application protocols that do not need guaranteed delivery use UDP

Gives Application protocol designers option for less overhead

UDP header smaller than TCP headers

UDP also faster as it does not stop and wait for acknowledgements of delivery

174


Common features Both connect applications

Both provide service so application can send data to correct application on destination host

Both use port numbers in their headers

Differences TCP has more functions, but slower because of them

UDP faster due to less overhead, but fewer functions including no error recovery

175


Table 10-3 TCP and UDP Comparisons

Feature TCP UDP Delivering data between two applications Yes Yes Identifying servers using well-known ports Yes Yes Segmenting data Yes No Guaranteed delivery through error recovery Yes No In-order delivery Yes No Flow control Yes No

176

Documents

Introduction to Networking ITT Version - YPW · Generic View of Converting from Binary IP Address to DDN Format. ... IPv4 address that begin with first octet between 0 and 127 Example