What is the Internet? Commercial worth of Internet The · 1969 Start of Internet project 1983 !214 hosts (50 in Arpanet ; 164 in MilNet) 1990! 200,000 hosts (start of “Internet”)

G Fairhurst, http://www.erg.abdn.ac.ukTheInternetProtocolSuite

The Network Layer (IP)

The Interface Layers (e.g. Ethernet)

Routing between networks

Transport (TCP, UDP, and applications)

G Fairhurst, http://www.erg.abdn.ac.ukWhat is the Internet?

1969 Start of Internet project1983 ! 214 hosts (50 in Arpanet ; 164 in MilNet)1990! 200,000 hosts (start of “Internet”)1995! 7 M hosts (30 M users)1997 22.5 M hosts (50 M users)2004 250 M hosts (798 M users ; 1/6 world population)2008 ???

One current estimate:! 2,300 M Telephones! 1,340 M Mobile phones ! 600 M PCs

Time to get a market of 50 Million People: Radio took 38 years TV took 13 years The Internet took 4 years

– Once opened to the general public

G Fairhurst, http://www.erg.abdn.ac.ukCommercial worth of Internet

Statistics from the IITF Report released on April 15, 1998 The Emerging Digital Economyhttp://www.ecommerce.gov/emerging.htm

InternetProtocol

Transport

Transport

Applications

Physical Layer

Links

Middleware

G Fairhurst, http://www.erg.abdn.ac.ukInternet Protocol Stack

G Fairhurst, http://www.erg.abdn.ac.ukIP Protocol Stack

IP

IP under everything emailwebVoIP

TVoIP

chatirc

ftp

IP on everythingEthernetFibre 3G

G Fairhurst, http://www.erg.abdn.ac.ukThe Power of IP

Layering of ProtocolsEnd-to-End Principle! decouple transmission from application! networks (IS) do not care what they carry! hosts (ES) do not care how it gets thereIP-hosts can control how they use the network

Profound impact on regulation

FTP

Ethernetdriver

server

FTP

Ethernetdriver

client

Middleware

IP

Enet Enet

InternetProtocol

Transport

Transport

Applications

Physical Layer

Links

“above the wire and below the application”

Middleware

G Fairhurst, http://www.erg.abdn.ac.ukSome Internet Players People expect Internet connectivity

“By the year 2016, no one under the age of forty will remember a world without personal computer. The

average twenty year old will find it hard to imagine a time when there wasn't any email to check or Web

sites to visit.”– George Christian, 2006.

G Fairhurst, http://www.erg.abdn.ac.uk

0

10000

20000

30000

40000

2008 2009 2010 2011 2012 2013

Web/EmailFile SharingInternet GamingInternet VoiceInternet Video to PCInternet Video to TVAmbient Video (webcams)


Video/Multimedia is Important!


IP AppliancesG Fairhurst, http://www.erg.abdn.ac.uk

InternetProtocol

The Connection-Less Network Service

The 20 byte IP Packet Header

IP Network Layer Addresses

Name Resolution (name to IP Address)

G Fairhurst, http://www.erg.abdn.ac.ukMessages (large blocks of data) are split into smaller pieces, called “Packets”

Each packet (PDU) has:

A header (known as the PCI)! Well-defined format! Destination address , source address, type, ...

A payload (known as the SDU)! A piece of the data to be communicated

IP Packets

139.133.1.2 139.133.1.3 139.133.10.7

139.133.204.18

Internet AddressesG Fairhurst, http://www.erg.abdn.ac.uk

129.23.5.9 Addresses of End SystemsG Fairhurst, http://www.erg.abdn.ac.uk

0 15 16 31

data

options (if any)32-bit destination IP address

32-bit source IP address16-bit header checksum

13-bit fragment offsetflags16-bit total length ToS/DSCPIHL4

16-bit identificationTTL protocol

20 bytes

IP Header

RFC 791

G Fairhurst, http://www.erg.abdn.ac.ukArranged in four levels:! Core Routers (No user networks connected)! Distribution Routers (Regional networks)! Access Routers (Internet Service Providers)! Home / Corporate networks

Internet Architecture

Name Resolution Name and Addresses

Flat v. Hierarchical Structures

The DNS

Mail to: [email protected]

I need to send to:abdn.ac.uk

139.133.1.2 139.133.1.3 139.133.10.7

139.133.204.18

Internet AddressesG Fairhurst, http://www.erg.abdn.ac.uk

G Fairhurst

Organisation of Names and Addresses

There are two ways of identifying a computer, using: ! A name! A network address

Names and addresses may be organised using:! A flat structure! A hierarchical structure

Organisation of names and addresses

G Fairhurst

Flat Structure

National Insurance Number

NZ 341865 B

Batch of numbersallocated to an officeSerial number

Number indicates issuingoffice and nothing aboutindividual

Flat StructureG Fairhurst

Lon171

Abdn1224

27 49

2201

Man1212

root

The Telephone Numbering System

Albania355

UK44

Uganda256

USA1

Zim263

2497

Country

Area

Exchange

Subscriber Line

ITU E.164

ITU Telephone Numbering System

bbc abdn ed

www erg cs

geographic domains generic domains

ukus edu org com

ieeeacco

The Domain name Service TreeG Fairhurst, http://www.erg.abdn.ac.uk

G Fairhurst

Hierarchical! ! ! ! ! ! Flat

Easy to remember! ! ! ! Difficult to remember

Abbreviated name possible! No unique abbreviations

Easy to find location of name! Only uniquely identifies

Difficult to change location!! Easy to change location

Locally administer names! ! Names allocated centrally

Flat v Hierarchical Structure

e.g. telephone no.PostcodeIP name (DNS)

e.g. social security no.IP address

Flat v Hierarchical Structure Internet Email



139.133.1.2 139.133.1.3 139.133.10.7

139.133.204.18

G Fairhurst, http://www.erg.abdn.ac.ukEvolution of the DNS

Most systems still also have a “/etc/hosts”and some also use a LAN name server

A single file ! /etc/hosts (in unix) ! entered by person setting-up computer

A central file (at internic.arpa)! downloaded to /etc/hosts (using ftp)

A distributed database ! clients send a request (query) ! a dns sends a response (resolution)


client needs to resolve a “name” to an “address”to communicate to destination

DNSServer

DNS StubResolver

DNS StackG Fairhurst, http://www.erg.abdn.ac.uk

Internet Email: dns query

Mail to: [email protected] need to send to:abdn.ac.uk

139.133.1.2

139.133.204.18dns stub resolver

“abdn.ac.uk”is 139.133.204.18


local dns server

Internet Email: dns response


139.133.1.2


“abdn.ac.uk”is 139.133.204.18


local dns server

Sending the Email


139.133.1.2


local dns server

Mail to:139.133.204.18

G Fairhurst, http://www.erg.abdn.ac.ukRecursive Lookup



local dns server

“abdn.ac.uk”is Y

“abdn.ac.uk”is 139.133.204.18

G Fairhurst, http://www.erg.abdn.ac.ukRecursion asks server to do what is needed to resolve

(recursion-bit set)

“uk.ac”is X

(referrals without recursion-bit set)“uk”is W

DNS Client Cache

DNS Client Request

Cache entryout of date?

In Local Cache? No

Yes

No

Yes

Use cachedvalue

Fetch value fromDNS server

Store in Cache

DNS Client Cache

DNS Cache



dns cache“abdn.ac.uk”is 139.133.204.18


dns cache“abdn.ac.uk”is 139.133.204.18

local dns server

DNS Records have various types:

MX records used for Mail Exchange

mail.abdn.ac.uk 3600 IN MX 500 backup.abdn.ac.ukmail.abdn.ac.uk 3600 IN MX 5 mailserver.abdn.ac.ukmail.abdn.ac.uk 3600 IN MX 10 mailserver1.abdn.ac.uk

Email uses the lowest numbered reachable mail server

Other formats also use the DNS:

http://www.abdn.ac.ukftp://ftp.abdn.ac.uksip://[email protected]

DNS RecordsG Fairhurst, http://www.erg.abdn.ac.uk

Browser/Application sends name to resolver (DNS client)Resolver checks own cache (local files, etc)If not resolved, contacts DNS Server

(resolver knows this IP address)If not resolved, contacts root DNS server (.)

May redirect to other server(s)Resolver given 1 or more addresses

(resolver caches the answer for some time)Browser/Application given lowest numbered server

DNS ResolutionG Fairhurst, http://www.erg.abdn.ac.uk

G Fairhurst

A name is a symbol - designed for human readingAn address is a data structure understood by a networkOrganisation may be hierarchical or flat

A name server provides a service to change betweennetwork addresses and network names

To know who's who on the Internet a computer must know the address of a name server

Naming & Addressing - SummaryNaming & Addressing: SummaryG Fairhurst, http://www.erg.abdn.ac.uk

Interface Layers (L1 & L2)

Encapsulation for Ethernet

Address Resolution Protocol (arp)


Addresses allocated to network as an address block! e.g. Aberdeen University allocated 139.133.x.x

Each System (ES or IS):! One (or more) unique IP address per NIC ! All addresses start with the same address prefix! e.g. 139.133.1.5, 139.133.208.1

IP LANsG Fairhurst, http://www.erg.abdn.ac.uk


Operating SystemKernel

le0 le1 lo0

EthernetDriver

Loop-BackDriver

EthernetController

EthernetController

UniqueInterface

Name

InterfaceSoftware

Physical Layer

Hardware

Network Layer

IP Interfaces

IP address 1 IP address 2

IP address 3


Sometimes a host doesnʼt know its IP address Quite common for dial-up, ADSL, etc ....

Internet Service Provider allocates an IP address (or pool of IP addresses)

Hosts request an IP address using DHCP (Dynamic Host Configuration Protocol)Send their MAC address, receive an IP address

Addresses may be loaned (for some time)or static assigned to a specific MAC address

Dynamic Host Configuration ProtocolG Fairhurst, http://www.erg.abdn.ac.uk

Addresses allocated to network as an address block! e.g. Aberdeen University allocated 139.133.x.x/16! i.e. addresses start with the same address prefix! e.g. 139.133.1.5, 139.133.208.1

Each System (ES or IS):! One (or more) unique IP address per NIC

IP Address AllocationG Fairhurst, http://www.erg.abdn.ac.uk


What happens if you join a new network?! Could configure IP address by hand

... but in practice need a better way

! DHCP allows this to be done automatically

Senders know:! MAC source address (may look in NIC ROM)Senders use DHCP to find their own IP addresses

This is automatic when end system connects to LAN

DHCP ServerG Fairhurst, http://www.erg.abdn.ac.uk

DHCP Example

Unicast:Client requests use

of the address

Unicast:DHCP serversends an offer

with details andan IP address to use

DHCPServerClient

Broadcast:Client sends

DHCP discoverwith own

MAC address

Unicast:DHCP serveracknowledges

request and providesa lease for some period


Clients broadcast to LAN to Discover DHCP server- includes own MAC address & “Magic Cookie”

One or more DHCP Server responds with a DHCP Offer:IP address that may be used;IP Subnet mask; IP address of default router; IP address of DNS server; IP address of DHCP server;“Magic Cookie” - nonce to identify request at server

Client responds to ONE server with a DHCP Request

Server responds with a DHCP AcknowledgmentValue used only for a specified period (lease interval)

DHCP Protocol


PayloadPAD

MACCRC

MACSource

6B 4B

MACDestination

MACType

2) Insert own MAC address (from PROM)1) Insert MAC address of destination (use arp)

3) Insert payload type code (0x800 for IP)4) Insert up to 1500 B payload (e.g. IP packet)

7) Prefix 8B preamble (including SFD)

5) Add padding if frame less than 60B (excl CRC)6) Calculate 32 bit CRC over the frame (signature)

Ethernet MAC Frame

6B 2B


MTU! Largest IP datagram (packet) which may be sent

IP packet (datagram) size 68-65535 B! Typically 1500B today using IPv4! Min MTU 1280 B using IPv6 [RFC 2460]

Fragmentation provided by senderLarger transport packets are fragmented to MTU.

Maximum Transfer Unit (MTU)

IP Datagram

MTU

MediumAccessControl

Transmission Control

Framing

IP

L1 (PL)

L2 (DL)

L3 (NL)

ARP

Other NL

G Fairhurst, http://www.erg.abdn.ac.ukIP Interfaces

ARP needed to set the destination MAC address


All systems connected to the Internet have a unique IP address

Systems know (or find out from DHCP) their IP address

Systems know the IP address of the destination(or find it out from the DNS)

Systems know their own MAC address(or can look in the NIC ROM)

No obvious way of determining destination MAC address - We will call the Next Hop IP address the Target-IP

Address Resolution Protocol (arp)G Fairhurst, http://www.erg.abdn.ac.uk

A B C

Where is C?

Broadcast: Who is C?

Unicast: I am Cmy addressis XXXXXX

ARP Request (send A -> C)

Not me,ignore thequery

arpmessage Padding Ethernet

CRCEthernetheader

14B 28B 4B18B

Ether Type = 0x806

Target IP

A has a packet to send to C

G Fairhurst, http://www.erg.abdn.ac.ukARP Example

Broadcast:arp who-is target-ip tell me Unicast:

arp target-ip is 08:00:20:1b:d4:90Unicast:

Application storedIP packet sent

with target MAC address

Application sends

Target IPQuerier

IP

ARP triggered,packet stored

G Fairhurst, http://www.erg.abdn.ac.uk0 15 16 318

Hardware Type Protocol TypeHLEN PLEN Operation

Sender HA (octets 0-3)Sender HA (octets 4-5) Sender IP (octets 0-1)

Sender !P (octets 2-3) Target HA (octets 0-1)Target HA (octets 2-5)Target !P (octets 0-3)

operation! ! message

! 1! ! ARP request! 2! ! ARP reply! [3! ! RARP request - ignore this]! [4! ! RARP reply - ignore this]

ARP/RARP Packet

RFC 826

Ether Type = 0x806


otherprotocolsN

IP inputIP output

demuxEthernet

frame type

ARP

dest =

local IP?

destinationin arp cache?

Y

Y

NN

dest =

broadcast?

Ycopy

loopback

Ethernet

Ethernet Driver

Ether Type = 0x806Ether Type

= 0x800

Ether Type = 0x800

Ether Type = 0x806

Packetsstored awaitingarp cache entry


Where are my friends?

32 bit IP target address

ARP/DHCP Packet32 bit

IP source address

Who am I?

48 bit Ether hardware address

48 bit Ether hardware address

RFC 2131


ARP: ----- ARP/RARP Frame -----ARP: Hardware type = 1ARP: Protocol type =0x0800 (IP)ARP: Length of hardware address = 6 bytesARP: Length of protocol address = 4 bytesARP: Opcode 0x0001 (ARP Request)ARP: Sender's hardware address = 8:0:20:b:b0:83ARP: Sender's protocol address = 10.0.0.17, dentARP: Target hardware address = ? (0xffff ffff ffff)ARP: Target protocol address = 10.0.0.80, (0x8b85 cc50)

!

gordon -> dent ARP R 10.0.0.80, gordon is 8:0:20:96:10:1a

dent -> (broadcast) ARP C Who is 10.0.0.80, gordon ?

ARP Packet

ARP

0x806


EthernetDriver

Incomingframe

ICMP IGMP

Ethernet Frame TypeIndicates how to demux

IP Protocol TypeIndicates how to demux

Transport Protocols

Protocol Demultiplexing

IP

0x800


Senders know:! IP source address (may use DHCP)! IP destination address (may use DNS)

.... and hence the Target-IP of the next-hop system! MAC source address (may look in NIC ROM)Senders use arp to find Target-IPʼs MAC addressesAn arp cache is needed to prevent overload!!The arp cache is also updated by any queryThe arp cache entries expire after a fixed periodIt is automatic when each packet is sent

arp Summary


012

...

6

...

17

...

255

345

3

2

3

1

3

IP Protocol

Type Byte

012345

inetsw[ ]ip_proto[ ]

Received IP Packet

Pointersto handlersfor transportprotocols

Table of pointers to entry in tableof IP protocols

Goto inetsw[ip_proto[packet[protocol]]];

IPUDPTCP

IP (raw)ICMPIGMP

IP Protocol Demux (Structures)G Fairhurst, http://www.erg.abdn.ac.uk

gresley:arp -amilliways-mac.erg.abdn.ac.uk (139.133.207.64) at 0:d0:bb:f7:c6:c1 on en0 mavis-mac.erg.abdn.ac.uk (139.133.207.77) at 8:0:20:86:ec:df on en0

ARP Example

The cache consists of a table of address and bindingsThere are currently two entries

Use the “arp -a” command to examine ARP cache.

G Fairhurst, http://www.erg.abdn.ac.ukARP Example

gresley:ping 139.133.207.111PING 139.133.207.111 (139.133.207.111): 56 data bytes64 bytes from 139.133.207.111: icmp_seq=0 ttl=60 time=1.732 ms...

gresley:ping 139.133.207.222PING 139.133.207.222 (139.133.207.222): 56 data bytesping: sendto: Host is downping: wrote 139.133.207.222 64 chars, ret=-1...

Each time a packet is made, arp is triggered as necessary to find the target-IPʼs mac address.Packets sent to 139.133.207.111 were received and generate replies.Packets sent to 139.133.207.222 generate no replies, we can assume this address is not in use.

Use the “ping” command to send test packets

G Fairhurst, http://www.erg.abdn.ac.ukgresley:arp -amilliways-mac.erg.abdn.ac.uk (139.133.207.64) at 0:d0:bb:f7:c6:c1 on en0 mavis-mac.erg.abdn.ac.uk (139.133.207.77) at 8:0:20:86:ec:df on en0

ARP Example

gresley:ping 139.133.207.111PING 139.133.207.111 (139.133.207.111): 56 data bytes64 bytes from 139.133.207.111: icmp_seq=0 ttl=60 time=1.732 ms...

gresley:ping 139.133.207.222PING 139.133.207.222 (139.133.207.222): 56 data bytesping: sendto: Host is downping: wrote 139.133.207.222 64 chars, ret=-1...

gresley:arp -amilliways-mac.erg.abdn.ac.uk (139.133.207.64) at 0:d0:bb:f7:c6:c1 on en0 mavis-mac.erg.abdn.ac.uk (139.133.207.77) at 8:0:20:86:ec:df on en0 erg2-printer.erg.abdn.ac.uk (139.133.207.111) at 0:10:83:ba:c0:a5 on en0 ? (139.133.207.222) at (incomplete) on en0 [ethernet]

The arp cache has two new entries:139.133.207.111 has MAC: 0:10:83:ba:c0:a5139.133.207.222 did not respond (no cache entry)


Two 10 Mbps Ethernet LANs are connected by a bridge. When monitoring LAN A for 1 minute, 40 arp requests are observed and 30 arp responses.(a) Calculate the Utilisation for the arp packets for LAN A.(b) Give two reasons why there are fewer responses than queries.

BRIDGELAN A LAN B

ARP QuestionG Fairhurst, http://www.erg.abdn.ac.uk

Two 10 Mbps Ethernet LANs are connected by a bridge. When monitoring LAN A for 1 minute, 40 arp requests are observed and 30 arp responses.

Calculate the Utilisation for the arp packets for LAN A.

Size of ARP request/Response is =8+14+28+4 (less than minimum Enet PDU) => 8+64 B= (70/60) x 8x72/107x100 % = 0.007%

ARP Question

Give two reasons why there may be fewer responses than queries.

(1) Some arp requests fail to complete (IP addr not used)(2) Some arp requests may have been sourced on LAN B and correspond to an IP address on LAN B. The response would not travel across the bridge.

001a 2f52 4841 000a 95cf ea5e 0806 00010800 0604 0002 000a 95cf ea5e 8b85 cf98001a 2f52 4841 8b85 cf40

G Fairhurst, http://www.erg.abdn.ac.ukARP Packet


Routing (L3)

Role of routers

Subnet mask

Default router


TheInternet

emps139.133.7.10

sysc139.133.7.110

isi.edu128.9.0.32

The Internet


RelayingMedia conversionIP SegmentationRoutingQuality of ServiceManagementSecurity

Role of Routers

RFC 1812

G Fairhurst, http://www.erg.abdn.ac.ukBridges v Routers

Bridges/SwitchesSeparate work group trafficImprove LAN performance

CheapWork at MAC Layer (mostly self configuring)Form one IP network (broadcast domain at L2)

RoutersConnect networksControl traffic flow between networks

More expensiveWork at Network Layer (e.g.IP)Connect different IP networksNeed configuration


End Systems send packet to an IP addressknow nothing about the network toplogy

About An IP Network

Routers use IP address to forward packetsknow nothing about ʻconversationsʼ


A) Local Network

B) Remote Network

Should the Local Network be used?

or

Should a router be used?

Selecting a Route

H0 H1

R0


data





20 bytes

IP Header

RFC 791

ES and routers always examine the IP destination address


IP Address

IP address! ! ! ! 139.133.7.110

netmask !! ! ! ! 0xffffff00 (255.255.255.0)

network ID! ! ! ! 139.133.7.0

net mask 1 11 1111 1 1 11 1111 1 1 11 1111 1 0 00 0000

0

network id host id

IP Subnet Mask

RFC 950

Block of addresses (32768 in this case)

ES need to know the network netmaskAll systems in a subnet must share same subnet mask

G Fairhurst, http://www.erg.abdn.ac.ukIP Subnet Mask

Subnet mask often writtenas a ʻ/ʼ followed by number of 1s in the mask

/8 11111111 00000000 00000000 00000000/9 11111111 10000000 00000000 00000000/10 11111111 11000000 00000000 00000000 /11 11111111 11100000 00000000 00000000 /12 11111111 11110000 00000000 00000000

/16 11111111 11111111 00000000 00000000/20 11111111 11111111 11110000 00000000/24 11111111 11111111 11111111 00000000/28 11111111 11111111 11111111 11110000

/29 11111111 11111111 11111111 11111000/30 11111111 11111111 11111111 11111100/31 11111111 11111111 11111111 11111110


Finding the network ID! Convert IP address to hex (or binary)! Convert netmask to hex (or binary)! Perform logical AND between the two

Example:

! IP address 139.131. 63. 53&!netmask 255.255. 0 . 0! host id is: 139.131. 0 . 0/16

Finding the Network ID G Fairhurst, http://www.erg.abdn.ac.uk

Identifying the Destination Network (1)Local network calculation

local IP address ! ! !139.133.7.110local network mask ! !255.255.255.0 local net +subnet id ! !139.133.7.0

dest IP address ! ! !139.133.7.10local network mask ! !255.255.255.0 dest net +subnet id ! !139.133.7.0

Remote network calculation

Compare

Match, thereforeuse local network

dest IP address ! ! !129.105.2.6local network mask ! !255.255.255.0 dest net +subnet id ! !129.105.2.0

Remote network calculation

G Fairhurst, http://www.erg.abdn.ac.ukIdentifying the Destination Network (2)Local network calculation

local IP address ! ! !139.133.7.110local network mask ! !255.255.255.0 local net +subnet id ! !139.133.7.0

Compare

Differ, usea router

G Fairhurst, http://www.erg.abdn.ac.ukEscaping from the LAN

Where is Z?

Sender forms packet withdestination address of Zand sends to Local Router

router forwardspacket on a link

Router understands the best linkto route a packet towards Z

Finding the Broadcast Address G Fairhurst, http://www.erg.abdn.ac.uk

Broadcast address = the network ID + all 1ʼs host ID

Finding the broadcast address! Convert IP address to hex (or binary)! Convert netmask to hex (or binary)! Perform logical OR of the inverted netmask

Example:netmask 255.255. 0 . 0

! IP address 139.131. 63. 53 OR 0 . 0 .255.255! host id is: 139.131.255.255


IP broadcast uses network addresswith a subnet value of all 1ʼs

To all systems in an IP network

Always sent using MAC broadcast

IP Broadcast

H0 H1

R0

ARP not needed

Routers neverforward

IP broadcastRouting (L3)

Routes

Traceroute

Routing Protocols

G Fairhurst, http://www.erg.abdn.ac.ukNetwork Layer Processing (IP)

IPIn

IPOut

Transport

SVC Man Routing SVC

NetInterface

NetworkLayer

Interface(Link, Physical)

Application software(and layers 5-7)Transport Layer

End System Stack

G Fairhurst, http://www.erg.abdn.ac.ukNetwork Layer Processing (IP)

IPIn

IPOut

IPIn

IPOut

IPIn

IPOut

IPForward

Transport

SVC Man Routing SVC

Control Plane

NetInterface

NetInterface

Data Plane(switching/forwarding fabric)

Interfaces

Routing Table

Services (application software)

TTL--

TTL=0?

TTL=64

Intermediate System Stack

NetInterface

NetInterface


Router Architecture1995 Single CPU designForwarding (data plane) Routing (control plane) and were closely linkedNetwork Interfaces standard NICʼsMost routers did both on the same CPU (PC-like)

2005 Separate Forwarding EngineForwarding (data plane) in hardware and Routing Interfaces optimised for forwarding(control plane) in a local CPU in same “box”

2010 Independent Forwarding EngineForwarding (data plane) in hardware and Routing (control plane) in a possibly separate box

Forwarding Plane

SVC Man Routing

NetInterface

NetInterface

NetInterface


PC Router Architecture

Control Plane

Single CPU design

Standard NICʼsLimited services:RoutingManagementAAA, etc

Forwarding Plane

SVC ManRoutingSVC

NetInterface

NetInterface

NetInterface

G Fairhurst, http://www.erg.abdn.ac.ukMultiservice Router Architecture

Control Plane

Control Plane

Multiple CPU design

Custom InterfacesMany services:Multi-protocol RoutingManagement, DHCP,AAA, VoIP,Web servers, Load balancing,Firewalls, NAT,Intrusion Detection

NetInterface

IPIn

IPForward

Transport

Routing

Routing Table

Routing Process

IPIn

IPOut

NetInterface

IPIn

IPOut

IPForward

Transport

Routing

NetInterface

Routing Table

IPOut


Route to zeno.ksc.nasa.gov (128.159.1.155),30 hops max, 40 byte packets

1 milliways-erg (10.0.0.64) ! ! ! 2 ms 1 ms 1 ms 2 139.133.210.1 (139.133.210.1) !! ! 7 ms 7 ms 7 ms 3 abdn-gw.abdn.ac.uk (139.133.7.6) ! ! 3 ms 3 ms 3 ms 4 smds-gw.ulcc.ja.net (193.63.203.33) ! 17 ms 16 ms 15 ms 5 nsn-gw.ulcc.ac.uk (128.86.1.3) ! ! ! 16 ms 17 ms 16 ms 6 128.161.165.1 (128.161.165.1) !! ! 96 ms 123 ms 147 ms 7 GSFC6.NSN.NASA.GOV (192.100.13.6) !98 ms 115 ms 146 ms 8 128.161.44.4 (128.161.44.4) ! ! ! 178 ms 189 ms 154 ms 9 MSFC1.NSN.NASA.GOV (192.100.14.1) 170 ms 178 ms 175 ms10 KSC.NSN.NASA.GOV (128.161.30.27) ! 192 ms 316 ms 168 ms11 192.150.33.1 (192.150.33.1) ! ! ! 192 ms 205 ms 213 ms12 128.159.215.239 (128.159.215.239) ! 172 ms 172 ms 193 ms13 163.205.253.254 (163.205.253.254) ! 330 ms 222 ms 269 ms

14 zeno.ksc.nasa.gov (128.159.1.155) ! 220 ms 377 ms 177 ms

Route to zeno.ksc.nasa.gov


194.247139.133

194.81

146.97

193.63

195.66

194.159

158.152

195.11

Web browser www.test.globalweb.co.ukWeb server

abdn.ac.uk

abman.net.uk

ja.net

linx-gw.ja.net

router.demon.net

scotland.net

18 hops in total over 9 domains (7 intermediate)

Route to globalweb.ac.ukG Fairhurst, http://www.erg.abdn.ac.uk

1 milliways (139.133.204.64) 2.831 ms 2.077 ms 2.167 ms 2 gw34.abdn.ac.uk (139.133.34.1) 4.828 ms 4.955 ms 4.865 ms 3 gwkccs.abdn.ac.uk (139.133.7.4) 16.989 ms 15.510 ms 5.331 ms 4 aclarke-gw.abman.net.uk (194.81.60.94) 7.769 ms 5.545 ms 5.734 ms 5 146.97.250.17 (146.97.250.17) 9.785 ms 12.061 ms 9.347 ms 6 146.97.37.29 (146.97.37.29) 13.904 ms 16.689 ms 11.144 ms 7 pos9-0.edin-scr.ja.net (146.97.35.61) 11.492 ms 16.527 ms 21.450 ms 8 pos0-0.leed-scr.ja.net (146.97.33.26) 18.450 ms 27.231 ms 19.766 ms 9 pos2-0.lond-scr.ja.net (146.97.33.30) 32.023 ms 35.862 ms 28.696 ms10 146.97.35.6 (146.97.35.6) 26.864 ms 25.046 ms 24.458 ms11 linx-gw.ja.net (193.63.94.249) 23.115 ms 32.644 ms 21.848 ms12 linx-2.router.demon.net (195.66.224.13) 26.371 ms 26.082 ms 22.430 ms13 tele-backbone-1-ge020.router.demon.net (194.159.252.54) 14 anchor-core-2-fxp1.router.demon.net (158.152.0.178) 15 demon-gw-2.sol.co.uk (195.11.50.130) 37.791 ms 33.314 ms 38.483 ms16 atm1-0-0-1.core2.scotland.net (194.247.77.34) 50.325 ms 56.771 ms 17 fe12-0-0.core1.scotland.net (194.247.67.41) 44.368 ms 46.100 ms 18 ABZ-Sci-Park.LL.scotland.net (194.247.71.109) 50.041 ms 51.625 ms

Traceroute to globalweb.ac.ukG Fairhurst, http://www.erg.abdn.ac.uk

139.133

194.81

146.97

193.63

198.32

129.7

Pegasus.phys.uh.eduWeb server

Web browser

abdn.ac.uk

abman.net.uk

ja.net

linx-gw.ja.net

ucaid.edu

gw.uh.edu

Route to phys.uh.edu


G Fairhurst, http://www.erg.abdn.ac.uk 1 milliways (139.133.204.64) 2.956 ms 2.103 ms 2.101 ms

2 gw34.abdn.ac.uk (139.133.34.1) 4.951 ms 4.891 ms 4.765 ms 3 gwkccs.abdn.ac.uk (139.133.7.4) 5.255 ms 16.300 ms 5.009 ms 4 aclarke-gw.abman.net.uk (194.81.60.94) 6.665 ms 5.533 ms 5.623 ms

5 146.97.250.17 (146.97.250.17) 10.686 ms 10.713 ms 9.235 ms 6 146.97.37.29 (146.97.37.29) 14.946 ms 20.399 ms 25.039 ms

7 pos9-0.edin-scr.ja.net (146.97.35.61) 14.822 ms 17.958 ms 20.820 ms 8 pos0-0.leed-scr.ja.net (146.97.33.26) 26.630 ms 26.973 ms 21.264 ms 9 pos2-0.lond-scr.ja.net (146.97.33.30) 28.960 ms 25.399 ms 25.840 ms10 146.97.35.6 (146.97.35.6) 22.284 ms 22.070 ms 23.392 ms11 us-gw2.ja.net (193.63.94.91) 28.271 ms 22.696 ms 23.660 ms12 193.62.157.18 (193.62.157.18) 91.709 ms 90.632 ms 87.277 ms13 ny-pop.i2.ja.net (193.62.157.210) 95.792 ms 95.864 ms 97.488 ms

14 clev-nycm.abilene.ucaid.edu (198.32.8.29) 106.189 ms 116.730 ms 15 ipls-clev.abilene.ucaid.edu (198.32.8.25) 113.960 ms 109.556 ms 16 kscy-ipls.abilene.ucaid.edu (198.32.8.5) 129.682 ms 126.980 ms

Traceroute to phys.uh.eduG Fairhurst, http://www.erg.abdn.ac.uk

17 dnvr-kscy.abilene.ucaid.edu (198.32.8.13) 138.995 ms 130.486 ms 18 scrm-dnvr.abilene.ucaid.edu (198.32.8.1) 153.115 ms 157.528 ms 19 losa-scrm.abilene.ucaid.edu (198.32.8.18) 163.873 ms 163.366 ms 20 hstn-losa.abilene.ucaid.edu (198.32.8.22) 195.996 ms 201.506 ms

21 LINK2ABILENE.GIGAPOP.GEN.TX.US (198.32.236.13) 194.006 ms 22 INTRALINK2IBT.GIGAPOP.GEN.TX.US (198.32.236.37) 199.774 ms 23 UH.GIGAPOP.GEN.TX.US (198.32.236.30) 205.365 ms 201.777 ms

24 vespasian-vlan10.gw.uh.edu (129.7.254.254) 205.210 ms 196.519 ms 25 Pegasus.Phys.UH.EDU (129.7.2.50) 204.640 ms 197.582 ms 204.103 ms

Traceroute to phys.uh.edu



data





20 bytes

IP Header

RFC 791

Router always examine the IP destination addressRouters may also utilise the ToS/DSCP valueThe TTL is decremented and checksum recalculated

4


net=

host route?

net=

network route?

default routespecified?

net =

local network?

Send ICMPmessageextract net

from IP address

Route IPdatagram

Send IPdatagram

arp request

destinationin arp cache?

Y Y Y Y

Y

N

N N NN

Router Forwarding ProcedureNetwork ID e.g. 10.1.0.0/16139.133.1.0/24


H0 H1 H2

R0

R2

R3

R1

Routing

H3

Itʼs not for my LANsend to local router (R0)

R3 is nearer H3,send to R3

R1 is nearest H3,send to R1

Itʼs on my LANuse arp to find h.a. send directly to H3

G Fairhurst, http://www.erg.abdn.ac.ukRouting Table

!

destination ! !route

139.133.208.x !localdefault ! ! !R0

destination ! !route

139.133.208.x !localN0 ! ! ! !localN1 ! ! ! !localN2 ! ! ! !R2N3 ! ! ! !R1139.134.x.x !R1

H0 H1 H2

H3

R0

R2

R3

R1

139.133.208.x

139.134.204.x

N0N1

N2N3


“Best Effort” network serviceNot all packets are deliveredSome may be delivered twice!Not all packets follow same routeNot all packets take the same time(Not all packets are segmented in the same way)

R0

R2

R1

Alternative RoutesG Fairhurst, http://www.erg.abdn.ac.uk

Routers exchange control packets

Routers send “control” messages! If you donʼt get them, you know link is “dead”

Thereʼs no such thing as a reliable “I am dead indication”This needs agreement between the two ends

R0

R2

R1

Routing ProtocolsG Fairhurst, http://www.erg.abdn.ac.uk

Routes from local networks

Default RouteA

Router B declares Router B as default routeRouter C declares Router B as default routeRouter D declares Router B as default routeAll traffic to “unknown addresses flows towards “core”

B CD

Default Route

Default Route

G Fairhurst, http://www.erg.abdn.ac.ukRoutes to Remote Networks

Route towards 10.1.0.0/16A

Router A instructs Router B Send B all traffic to addresses with network ID 10.1.0.0/16Router B sends traffic with network ID 10.1.1.0/24 to CRouter B sends traffic with network ID 10.1.3.0/24 to D

B CD

Route towards 10.1.1.0/24

Route towards 10.1.3.0/24

G Fairhurst, http://www.erg.abdn.ac.ukLink ProtocolControllers(e.g. Ethernet)

Network Protocol(Forwarding Engine)

Hardware Address Tables

InterfaceManagement Table

Forwarding Table(IP address matchesanother local interface)

Interface to/from Packet Switch

Receivedpacket

Forwardedpacket

Router ArchitectureG Fairhurst, http://www.erg.abdn.ac.uk

Router Architecture

Hardware Packet Switch(connects via general purpose processor)

Network Interface Cards(here with single interfaces)

Receivedpacket

Forwardedpacket

Forwarding table(identifies this packet requiresprocessing by general purpose processor)

General Purpose Processor(examines packet header in detail, perhaps using filter table)

Forwarding Plane

SVC SVC

NetInterface

NetInterface

Control Plane

G Fairhurst, http://www.erg.abdn.ac.ukRouter Platform

Home Gateway(cost)

Office Router(control)

ISP Router(interfaces)

Core Router(speed)

ServicesPlatform(flexibility)

WebServer

Not all routers are equal- Cost is sometimes important- Control is sometimes important- Speed is sometimes important- Services are sometimes important

Price v RouterPerformance

Instructions/Packet

Cost/Bandwidth

FabricEngine

CoreRouter

EdgeRouter

ServicesPlatform

PC

1 10 100 1000 10000 100000

G Fairhurst, http://www.erg.abdn.ac.ukNAT

First invented to map one computer to one addressReally useful in a commercial setting

This lets a company change itʼs external IP address


NAPTPort TranslationNAPT shares same address between multiple usersGenerally what is done for home networksConnections have to be started from the inside

- Becomes a nuisance when connecting to a serverNAPTs build state

- When a NAPT crashes the connections disappearNATs try to be “transparent”, it hides and doesthings without anyone asking it to do things

G Fairhurst, http://www.erg.abdn.ac.uk G Fairhurst, http://www.erg.abdn.ac.uk

ICMPInternet Control Message Protocol

ICMP Encapsulation

Ping and ICMP Echo

Other uses: PMTU Discovery, Traceroute

G Fairhurst, http://www.erg.abdn.ac.ukInternet Control Message Protocol

Routers / Computers send ICMP messages

Messages usually contain the header of the packet

Not usually sent when ICMP messages received(An exception is an ICMP ECHO REQUEST)

Problem

H1R0 R2R1H0

ICMP(Reason, Diagnostic)

G Fairhurst, http://www.erg.abdn.ac.uk0 15 16 317 8

8-bit type 8-bit code 16-bit checksum

(contents depend on type and code)

Type! Message

0! ! Echo reply3! ! Destination unreachable4! ! Source quench5! ! Redirect8! ! Echo request11! ! Time exceeded (i.e. TTL=0)!

ICMP Message

Postel, J., "Internet Control Message Protocol", RFC792, STD 5, 1981.

G Fairhurst, http://www.erg.abdn.ac.ukICMP Encapsulation

user data

Usually contains "ID" and "sequence number"for "ICMP Echo"

user dataICMPheader

4

20

IPheader user dataICMP

header

Ethernetheader

EthernetCRC-32

14 4IP

header user dataICMPheader


ping -s sysbPING sysb: 56 data bytes64 bytes from sysb (139.133.201.196): icmp_seq=0. time=3. ms64 bytes from sysb (139.133.201.196): icmp_seq=1. time=3. ms64 bytes from sysb (139.133.201.196): icmp_seq=2. time=3. ms64 bytes from sysb (139.133.201.196): icmp_seq=3. time=3. ms64 bytes from sysb (139.133.201.196): icmp_seq=4. time=3. ms64 bytes from sysb (139.133.201.196): icmp_seq=5. time=3. ms64 bytes from sysb (139.133.201.196): icmp_seq=6. time=3. ms64 bytes from sysb (139.133.201.196): icmp_seq=7. time=3. ms64 bytes from sysb (139.133.201.196): icmp_seq=8. time=3. ms64 bytes from sysb (139.133.201.196): icmp_seq=9. time=4. ms64 bytes from sysb (139.133.201.196): icmp_seq=10. time=5. ms64 bytes from sysb (139.133.201.196): icmp_seq=11. time=3. ms^C----sysb PING Statistics----12 packets transmitted, 12 packets received, 0% packet lossround-trip (ms) min/avg/max = 3/3/5

Ping of Local Host

RTT = 2 ms

Ping 60 B of ICMP payload


ping -s www.ksc.nasa.govPING zeno.ksc.nasa.gov: 56 data bytes64 bytes from zeno.ksc.nasa.gov (128.159.1.155): icmp_seq=0. time=191. ms64 bytes from zeno.ksc.nasa.gov (128.159.1.155): icmp_seq=1. time=237. ms64 bytes from zeno.ksc.nasa.gov (128.159.1.155): icmp_seq=2. time=412. ms64 bytes from zeno.ksc.nasa.gov (128.159.1.155): icmp_seq=3. time=177. ms64 bytes from zeno.ksc.nasa.gov (128.159.1.155): icmp_seq=4. time=183. ms64 bytes from zeno.ksc.nasa.gov (128.159.1.155): icmp_seq=5. time=189. ms64 bytes from zeno.ksc.nasa.gov (128.159.1.155): icmp_seq=6. time=179. ms64 bytes from zeno.ksc.nasa.gov (128.159.1.155): icmp_seq=7. time=177. ms64 bytes from zeno.ksc.nasa.gov (128.159.1.155): icmp_seq=8. time=174. ms64 bytes from zeno.ksc.nasa.gov (128.159.1.155): icmp_seq=9. time=175. ms64 bytes from zeno.ksc.nasa.gov (128.159.1.155): icmp_seq=10. time=178. ms64 bytes from zeno.ksc.nasa.gov (128.159.1.155): icmp_seq=11. time=189. ms64 bytes from zeno.ksc.nasa.gov (128.159.1.155): icmp_seq=12. time=322. ms^C----zeno.ksc.nasa.gov PING Statistics----14 packets transmitted, 13 packets received, 7% packet lossround-trip (ms) min/avg/max = 174/214/412

Ping of Remote HostG Fairhurst, http://www.erg.abdn.ac.uk

Segmentation / Fragmentation

IP segmentation by routers

IP segmentation header

Path MTU Discovery

End System segmentation by sender

G Fairhurst, http://www.erg.abdn.ac.ukIP Segmentation

Each Interface has a Maximum Transmission UnitThe MTU specifies the size of the largest IP packetPackets must be fragmented to be less than the MTU


Own MAC hardware address (from NIC PROM)! Used in MAC source address

Own IP address (given by network administrator)! Used as IP source address

Own IP subnet mask (given by network administrator)! Indicates remote destination addresses! Indicates IP broadcast address (to all local systems)

IP default router (given by network administrator)! IP address of router to send to for remote addresses! (indicates MAC address for remote IP networks)

IP name server server (given by network administrator)! IP address of a server to resolve names <-> address

Required InformationG Fairhurst, http://www.erg.abdn.ac.uk

Transport,Middleware & Applications

UDP (Header, Services)

Demultiplexing (Protocol, Port)

Checksum

TCP (Header, Services)

TCP Connections

Applications

1980s: Reliable data transmission

Data was precious... Networks needed to be careful not to loose/damage it.

1980


1980s: The Internet model

In most places, the Internet is only “best effort”There can be:

Loss (never arrives)Variable delay (arrives late)Reordering (wrong order)

All much more common with wireless


Reliability needs to be End-to-End

"The function in question can completely and correctly be implemented only with the knowledge and help of the application standing at the end points of the communication system. Therefore, providing that questioned function as a feature of the communication system itself is not possible."

TCP

TCPDave Clarke, 1981

G Fairhurst, http://www.erg.abdn.ac.uk G Fairhurst, http://www.erg.abdn.ac.ukNetwork Layer Processing (IP)


IPIn

IPOut

Transport

SVC Man Routing SVC

NetInterface

NetworkLayer

Interface(Link, Physical)

Transport

Transport

G Fairhurst, http://www.erg.abdn.ac.ukTransport Layer Service

End System

End System

Logical link between applications

Transport protocols run in End Systems

Several Transport Protocols(ICMP)UDP, TCP, STCP, UDP-Lite, DCCP


UDP User Datagram ProtocolBest Effort Service

Multiplexing (service access points)

Integrity Check


## Internet (IP) protocols#ip 0 IP # internet protocolicmp 1 ICMP # internet control message protocoltcp 6 TCP # transmission control protocoludp 17 UDP # user datagram protocol## Internet (IPv6) extension headers#ipv6 41 IPv6 # IPv6 in IP encapsulation... More IPv6 Extension Headers...

In UNIX, these are stored in /etc/protocols

IP Protocol Types

IP

Incomingpacket

IP ICMP

IP Protocol TypeIndicates how to demux

Transport Protocols

IP in IP Tunnel


0 15 16 31

8 bytes16-bit source port 16-bit destination port 16-bit UDP length 16-bit UDP checksum

data (if any)

UDP Header

(dest IP, dest port))

Integrity checked by:! Verifying the length of PDU (incl. header)! Executing a checksum algorithm

RFC 768

Each connection identified by:


Transmission Frame Corruption (link CRC fails)Router Header Corruption (IP Checksum fails)Router Congestion (packet discarded by router)Receiver Busy (packet discarded by end system)No route to destination (packet discarded by router)Equipment failure (packet discarded by router)Each means packet does NOT reach the destination

Why are datagram networks unreliable?

Loss in NetworksG Fairhurst, http://www.erg.abdn.ac.uk

Corruption of packet:! inside bridges! inside routers! inside end systems! Causes: ! Software errors (copy wrong data)! DMA hardware faultsErrors in IP header detected by IP checksum! Routers discard packets with header errorsErrors in IP payload undetectedA corrupted packet can reach the destination

Why are datagram networks unreliable? (II)

Corruption in Networks

G Fairhurst, http://www.erg.abdn.ac.uk16-Bit UDP Checksum

Sender treats segment contents as sequence of 16-bit integersAdd (1ʼs complement sum) of segment contentsPut checksum value into UDP checksum field

Receiver computes checksum of received segmentIs computed checksum equals checksum field value:

NO - error was detected.YES - no error detected. But, may be errors nonetheless?

Some other things to check:Addresses, Length, ProtocolThese are also added into checksum


Server

C2

C1

C3 C4

Internet

Port Numbers

Each client sends packet with a specified Destination Port

The Server accepts packet to a socket bound to Destination Port

G Fairhurst, http://www.erg.abdn.ac.ukWell-Known Server Port Number

IP

Ethernetdriver

Application

Transport

Network

Data Link

Physical Layer

Server “opens” a new transport session

It “binds” to(dst = server-port, src= any-port)

It “accepts” new connections

I will accept packets from server-port


Some examples are:37 !Network time Server (nntp)53!! ! Domain Name Server (dns)

e.g. packets sent from a client to a dns server (53)IP header! ! ! ! ! ! ! UDP header(clientʼs IP addr, dns server IP addr) ! (client port,53)e.g. packets (responses) from a dns server(3) to a clientIP header! ! ! ! ! ! ! UDP header(dns server IP addr, clientʼs IP addr) ! (53, client port)

The Internet has agreed a set of well -known portsThere are lots of these - one for each service

Well Known Port NumbersG Fairhurst, http://www.erg.abdn.ac.uk

Unique Client Port Number

IP

Ethernetdriver

Application

Transport

Network

Data Link

Physical Layer

Client “opens” a new transport session

It “binds” to(src = unique-port,dst = server-port)

I want to send to server-port

G Fairhurst, http://www.erg.abdn.ac.ukUnique Client Port Number

Connections identified by: {SIP,SPort,DIP,DPort}How do you choose SPort?

SPort needs to be unique for a clientCould increment for each new socket

(some OS do)But... could do something different

(many OS do)Could pick a random (but unique) SPort

(makes packet snooping harder)

G Fairhurst, http://www.erg.abdn.ac.ukSrc &Dest Port Numbers

IP

Ethernetdriver

IP

Ethernetdriver

Application

Transport

Network

Data Link

Physical Layer

(unique,well-known)

(well-known,unique)

Server(well-

known)Client

(unique)All UDP packets carry(src, dst) port numbers

G Fairhurst, http://www.erg.abdn.ac.ukSimple Services! Startup / Bootstrap !(DHCP, tftp)

Query / Response! Disk Sharing !! ! ! (nfs)! Address Query! ! ! (dns)! Time Query! ! ! ! (ntp)! Network Management ! (snmp)

Stream Services! Audio, Video!! ! ! (Multimedia)! Internet Telephony! ! (Voice over IP)

Multicast! Internet TV! ! ! ! (Multicast Multimedia)! File Distribution! ! ! (Multicast File Transfer)

UDP ServicesG Fairhurst, http://www.erg.abdn.ac.uk

TFTPTrivial File Transfer Protocol

Reliability

Packet Headers

Retransmission (ARQ)

VERY simple file transfer protocol.

First defined in 1980.

Easy to implement in a very small amount of memory.

TFTP is useful for booting computers and configuring routers which did not have mass storage devices.

Can be used to transfer small files between hosts on a LAN, e.g. remote X Window System terminal.

G Fairhurst, http://www.erg.abdn.ac.ukTrivial File Transfer Protocol (TFTP)

G Fairhurst, http://www.erg.abdn.ac.ukTrivial File Transfer Protocol (TFTP)

Read Request (RRQ)

No software whenclient switched on,requests copyfrom server

copy of client software(e.g. “bootstrap, 1074 B)

DATA ACK

Internet is Best Effort! Some information may be lost in transit

Corruption unlikely (due to CRCs and checksums)

Reliability Implies....

! All information is received!! (no loss, no residual errors)! No information is duplicated !(no extra copies)!Sequencing !! ! ! ! ! (original order is preserved)

ReliabilityG Fairhurst, http://www.erg.abdn.ac.uk

ACK ACK

D

ACK

Send a Packet Wait Acknowledged

"I got it!"

D D

Automatic Repeat reQuest (ARQ)G Fairhurst, http://www.erg.abdn.ac.uk

Transmit Timer

Transmit timer monitors receipt of acknowledgments

Starts:!When first Data Packet sent

Restarts:!When a new Data Packet sent

Stops:!When all packets have been acknowledged


ACK ACK

D1 D2 D2'

"I got it!" Lost packet

Timer Timer

"What, no ACK?- send it again."

Timerstopped

Timerstarted

Timerrestarted

"I got it!"

Timerrestarted

Timer

Loss Recovery by Timer G Fairhurst, http://www.erg.abdn.ac.uk

Advantages Very simple to implement

Disadvantages Response to every transmitted Data packet Timers needed to recover loss of a Data packet/ACK Wasteful with long delays

Stop & Wait ARQG Fairhurst, http://www.erg.abdn.ac.uk G Fairhurst, http://www.erg.abdn.ac.uk

Trivial File Transfer Protocol (TFTP)

READrequest(RRQ)

Serverstartstransfer

DATA 1 (512 B)

DATAindication

ACK(1)

DATA 2 (512 B)

DATAindication

ACK(2)

DATA 3 (50 B)

DATAindication

Last block< 512B,indicates endof transfer.

ACK(3)

G Fairhurst, http://www.erg.abdn.ac.ukTFTP Protocol Header

Data block4B

8 B UDP

20 B IP

Op Code 2 B sequence number

Op Codes for TFTP1 = TRead Request (RRQ)2 = Write Request (WRQ)3 = DATA (512 B, unless final)4 = ACK5 = Error

TFTP defined in RFC 1350, 1992


Defined as “the number of bits transferred per second from a given layer to the upper layer as a result of a conversation between two users of the layer”Considers only data forwarded to the OSI layer above(i.e. not layer ovehead)Expressed in bits per secondMeasures performance of a layer

Throughput

! Throughput = (PDU)/(RTT)

DATA

ACKRTT Idle time

G Fairhurst, http://www.erg.abdn.ac.ukThroughput

! TFTP is very simple to implementUses UDP/IPAdds to this to provide reliable deliveryUseful for simple tasks (software download, configuration of routers, etc)Performance OK for a LAN

Not suited to general InternetSlow performance with large delayNo userid/loginNo congestion control (see “TCP”)

G Fairhurst, http://www.erg.abdn.ac.ukSummary


TCP Transmission Control ProtocolIntegrity Check (as UDP)

Multiplexing (similar to UDP)

Reliable In-Order Delivery (retransmits)

Stream-oriented Transport

Flow Control (receiver slows-down sender)

Congestion Avoidance (network slows-down sender)

Out-Of-Band Data (little used)


FTPclient

TCP

IP

Ethernetdriver

FTPclient

TCP

IP

Ethernetdriver

Application

Transport

Network

Data LinkPhysical Layer

FTP between local hosts

Reliable

(source IP, source port; Dest IP, dest port)


user data

user dataapplicationheader


TCPheader


TCPheader

IPheader

Ethernetheader user dataapplication

headerTCP

headerIP

headerEthernetCRC-32

20

20

14 4

Encapsulation

G Fairhurst, http://www.erg.abdn.ac.ukTCP Streams

write

write

write

readreadreadread

≤ MSS

Sender Receiver


0 15 16 31

20 bytes

16-bit source port 16-bit destination port32-bit sequence number

32-bit acknowledgement numberTCPHL reserved flags 16-bit window size

16-bit TCP checksum 16-bit urgent pointeroptions (if any)

data (if any)

TCP Header

RFC 793

Same as UDP

Data and ACK sequence numbers

G Fairhurst, http://www.erg.abdn.ac.ukTCP Services

Interactive Services! terminal access (telnet [23] rlogin [513])! dns

Bulk Services! file transfer (ftp [21])!! mail transfer (smtp [25])! streaming mediaSemi-Interactive!!! WWW (http [80])! nfs


Some examples are:

20 FTP-DATA File Transfer [Default Data]21 FTP File Transfer [Control] 23 TELNET Telnet 25 SMTP Simple Mail Transfer 37 TIME Time 69 TFTP Trivial File Transfer79 FINGER Finger110 POP3 Post Office Protocol v 3123 NTP Network Time Protocol143 IMAP2 Interim Mail Access Prot. v2 161 SNMP Simple Network Man. Prot.

The Internet has agreed a set of well -known ports

There are lots of these, see: ! /etc/services file in UNIX! or RFC 1060 (Assigned Numbers)

Well Known Port NumbersG Fairhurst, http://www.erg.abdn.ac.uk

Stop and Wait Protocol!Throughput = (PDU)/(RTT)

Window-Based Protocol!High throughput requires large enough window.! ! (window(in bytes)xRTT) > bandwidth

ACK

DATA

Idle time

ACK

DATA

DATA

DATA

DATA

DATA

WindowG Fairhurst, http://www.erg.abdn.ac.uk

Defined as “the number of bits transferred per second from a given layer to the upper layer as a result of a conversation between two users of the layer”Considers only data forwarded to the OSI layer above(i.e. not layer ovehead)Expressed in bits per secondMeasures performance of a layer

Throughput


Defined as “the total number of bits transferred at the physical layer to communicate a certain amount of data divided by the time taken to communicate the data.”Includes all bits in all types of frame irrespective of whether they are corrupted or correctly received. Expressed as a percentage of physical layer rate.Measures link capacity used.

Utilisation!Idle (unused)

Utilised!


! An end system uses TCP to communicate with another end system over a 10 Mbps Ethernet LAN. The sender transmits 50 packets per second with 1460 B of TCP data, and receives 25 packets per second of Acknowledgements (ACKs) with no data.

Calculate:! (i) The throughput ! (ii) The utilisation of the network! (iii) The utilisation if UDP were used instead of TCP

G Fairhurst, http://www.erg.abdn.ac.ukMultiplexing

Two flows can share a link (multiplexing)Utilisation = sum of each flow utilisationNo loss occurs providing utilisation < 100%Some buffer space is needed to store bursts

Sharing

• Circuit-switching allocates fixed capacity

• Peak packet rate can exceed long-term share

G Fairhurst, http://www.erg.abdn.ac.uk G Fairhurst, http://www.erg.abdn.ac.ukCongestion

More packets received than sent ! !! queue buildsQueue exceeds buffer memory! packets discardedKnown as a “drop-tail” router

G Fairhurst, http://www.erg.abdn.ac.ukCongestion Collapse

Retransmit the discarded packets!! causes more overloadSituation results in a “meltdown”Known as a “congestion collapse”

“Route” Optimisation Problem

ES can optimise globally

ISP-level optimisation more course-grain


Multi-path sharing

Takes sharing one stage further

Leverages multi-homing

Traffic moves away from congested links

G Fairhurst, http://www.erg.abdn.ac.uk G Fairhurst, http://www.erg.abdn.ac.uk

Congestion Collapse was a real problem in late 80ʼs

It was prevented by new algorithms in TCP (1986)

! Each TCP sender now judges how fast to send! - based on whether they experience congestion:

End Systems that see any loss slow down.End Systems that do NOT see loss speed up.

! Use of this is required (1988)! It has worked very well - at least up until now!

TCP continues to evolve......

Congestion Avoidance

A New Internet Layer?

InternetProtocol

Transport

Links and Physical

Transmission


Current Internet

(1981)

IPv6

Next Gen. Internet(1994)

IPv4 IPv6

G Fairhurst, http://www.erg.abdn.ac.ukIPv4

32-bit address Monolithic header (complex)

Options not widely implementedRouter fragmentation troublesome (use PMTUD)

Version HLen DSCP/ToS

ProtocolTime to Live

Total Datagram Length

Fragment Identification Fragmentation OffsetFlags

Header Checksum

32 bit Source Address

32 bit Destination Address

Options (if any), multiple of 32 bits

ECN

Field updated and present in IPv6 base header

Field not present in IPv6 base header


“New” IPv6 Functions

Simplified header format (good for hardware)Expanded addressing 128-bitImproved support for Extensions (e.g. mobility)Flow LabelingAuthentication and Privacy (IPsec, SEND, ...)

Version DSCP/ToS

Hop Limit

Flow Label

Payload Length

128 bit Source Address

ECN

Next Header

128 bit Destination Address

Header Extensions (if any)

Header LengthNext Header


0000: 47 5c 8f 15 00 80 6c 86 dd 60 00 00 00 00 40 3a G\....l..`....@:

0010: 40 20 10 0d b8 85 a3 08 d3 13 19 8a 2e 03 70 73 @ ............ps

0020: 35 20 10 0d b8 85 a3 08 d3 13 19 8a 2e 03 70 73 5 ............ps

0030: 35 80 00 e9 6b 77 3d 00 04 9b 56 d9 47 00 00 00 5...kw=...V.G...

0040: 00 3e 0f 0d 00 00 00 00 00 10 11 12 13 14 15 16 .>..............

0050: 17 18 19 1a 1b 1c 1d 1e 1f 20 21 22 23 24 25 26 ......... !"#$%&

0060: 27 28 29 2a 2b 2c 2d 2e 2f 30 31 32 33 34 35 36 '()*+,-./0123456

0070: 37 8f 05 4a 29 ff ff ff ff ff ff ff ff ff ff ff 7..J)...........

0080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ................

0090: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ................

00a0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ................

00b0: ff ff ff ff ff ff ff ff ff ff ff ff ............

G Fairhurst, http://www.erg.abdn.ac.ukIPv6 Decode

Standard on all router platforms

Common on high-end switches

Standard in modern host operating systems

“IPv6 is not Rocket Science” – Lorenzo Colitti

http://www.ipv6forum.com/

But...

0.39% of BGP-advertised prefixes are IPv6!

0.2% of total web traffic!

G Fairhurst, http://www.erg.abdn.ac.ukIPv6 Status

Some features were not used:

Flow-labels not so useful after all

IPsec mainly used for VPNs

Many IPv6 features now in IPv4:

QoS

Multicast

Mobility

NAT has replaced the need for addresses?

“...Itʼs not deployed, do we need IPv6?”

IPv4 IPv6

G Fairhurst, http://www.erg.abdn.ac.ukIPv6 Features Distribution of allocated IPv4 Addresses

USA32%

Asia/Pacific31%

Europe28%

Lat America7%

Africa2%

USA Asia/Pacific Europe Lat America Africa

Areas with high demand for rural satellite Internet have few IPv4 addresses


0

20

40

60

8078

73

65 65 65

62 62

59

55

49 49

45

4241

39

35

Dec-04Jul-05

Dec-05Jun-06

Dec-06Jun-07

Dec-07Jun-08

Unallocated IANA IPv4 /8 Addresses

~9 /8’s allocated per year

http://www.potaroo.net/tools/ipv4/index.html

the days of free IPv4 addresses are numbered...Projected IANA Unallocated Address Pool Exhaustion: 20-Jun-2011


So what will the Future Internet be?

An Internet that builds on IPv4

Internet will continue to evolve slowly...

An Internet that deploys IPv6

NAT-free host-to-host via IPv6

Autoconfig /provider-independent addressing

Mobility (?)

And new stuff...

A “clean slate” design of a new network architecture

Transition to something better

??


?

Packet DecodesEthernet Header

PDU Header Chart

Hexadecimal Packet dump 0: 0100 5e02 dc3e 00d0 bbf7 c6c0 0800 4500

16: 00cc e206 0000 7111 a1a9 84b9 8476 e002 32: dc3e 7982 7982 00b8 08a0 8005 dbc6 d721 48: 69c0 0752 bb5f fe39 3600 8808 b120 8933 64: 6219 9118 5128 ffc8 1321 bc10 933e aa23 80: 3233 ba00 e892 a00c 1a3c 0a28 37ab 012d 96: aca5 4819 9088 0b39 64ba 43a0 b9a8 04b3 112: 88b8 4bf8 3940 d024 0a98 8b0b 1703 0a3a 128: 8820 a381 a21f 3bc0 9298 e893 90bd 042a 144: 0a88 3287 59ab e980 1211 4002 2208 98b1 160: 7039 0b26 e898 99ab b118 a1aa a702 9ac4 176: 9128 ca21 7822 2971 090a 2194 98d0 27bb 192: 0958 8092 993f b3b0 2922 337a 0f88 8810 208: 8a29 0183 fb15 b888 0d4c


data



13-bit fragment offsetflags16-bit total length ToSIHL4


20 bytes

IP Header

RFC 791


0 15 16 31

8 bytes16-bit source port 16-bit destination port 16-bit UDP length 16-bit UDP checksum

data (if any)

UDP Header

RFC 768

ETHERPacket size = 218 bytesDestination = 1:0:5e:2:dc:3e, (multicast) (01-00-5e-02-dc-3e)Source = 0:d0:bb:f7:c6:c0, Ethertype = 0800 (IPv4)IPVersion = 4, Header length = 20 bytesType of service = 0x00Total length = 204 bytes (00cc)ID = 57862, Flags = 0x00, Frags = 0Time To Live = 113 seconds/hopsProtocol = 17 (UDP)Header checksum = a1a9Source address = 132.185.132.118Destination address = 224.2.220.62No optionsUDPSource port = 31106 (7982)Destination port = 31106 (7982)Length = 184 (00b8)Checksum = 08a0 RTP180B of Data

0: 0100 5e02 dc3e 00d0 bbf7 c6c0 0800 4500 16: 00cc e206 0000 7111 a1a9 84b9 8476 e002 32: dc3e 7982 7982 00b8 08a0 8005 dbc6 d721 48: 69c0 0752 bb5f fe39 3600 8808 b120 8933 64: 6219 9118 5128 ffc8 1321 bc10 933e aa23 80: 3233 ba00 e892 a00c 1a3c 0a28 37ab 012d 96: aca5 4819 9088 0b39 64ba 43a0 b9a8 04b3 112: 88b8 4bf8 3940 d024 0a98 8b0b 1703 0a3a 128: 8820 a381 a21f 3bc0 9298 e893 90bd 042a 144: 0a88 3287 59ab e980 1211 4002 2208 98b1 160: 7039 0b26 e898 99ab b118 a1aa a702 9ac4 176: 9128 ca21 7822 2971 090a 2194 98d0 27bb 192: 0958 8092 993f b3b0 2922 337a 0f88 8810 208: 8a29 0183 fb15 b888 0d4c

EncapsulationG Fairhurst, http://www.erg.abdn.ac.uk

Topics to be examined- Everything on the syllabus (includes lab & tutorials)

Topics excluded- Calculation of link CRC (but know what it does!)- Algorithm for DPLL (but know what it does!)- Calculation of packet checksum (but know what it does!)

Topics not covered this year- IP router fragmentation- Path MTU Discovery

And finally....

Documents

What is the Internet? Commercial worth of Internet The · 1969 Start of Internet project 1983 !214 hosts (50 in Arpanet ; 164 in MilNet) 1990! 200,000 hosts (start of “Internet”)