Internetworking - · PDF fileimplementasi yang berbeda pada protokol bawah ... 127.x.y.z digunakan utk loopback testing ... Src Link-Level Addr = E1 Dest Addr =

Semester Genap 2003/2004Versi: 2

Jaringan Komputer

Fakultas Ilmu KomputerUniversitas Indonesia

Internetworking(Week 8 & 9)

2 Versi: 2

Agenda

Problem: There is more than one network!Simple Internetworking (Bab 4.1)

• Basis internetwork (Bab 4.1.1)• Service model (Bab 4.1.2)• Global Address & ARP (Bab 4.1.3, 4.1.5)• Datagram Forwarding: IP (Bab 4.1.4)• Host Configuration: DHCP (Bab 4.1.6)• Error Reporting: ICMP (Bab 4.1.7)• Virtual Networks & Terminals (Bab 4.1.8)

Routing (Bab 4.2)Global Internet (Bab 4.3)Multicast (Bab 4.4)

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The Big Picture: Internetworking

You are here, chapter 4

000100011100100100011101

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Review (… so far)

UnderstandBagaimana bentuk/dasar jaringan: host terhubung langsung => link tunggal (one physical medium)Bagaimana membangun jaringan lebih besar(connected networks: switch & bridges).

Internetworking Masalah variasi dan heterogenitas jaringan => implementasi yang berbeda pada protokol bawah(layer 1 & 2) dan hardware.Membahas jaringan yang berkembang menjadi sangat besar, mis. Internet (scalability issues).

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Scope: Internetworking

Rincian topik internetworkingBasis internetworking: IP protocol, address resolution, & control messagesTopik (in-depth): routingTopik (sekilas): global internets (scale)

• virtual geography and addresses• hierarchical routing• name translation and lookup• multicast traffic• future internetworking: IPv6

Rujukan: [PET00] Peterson and Davie 2nd

ed., ch. 4

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Basics of Internetworking

Apa yang disebut: internetwork?Ilusi terhadap koneksi seperti: suatu jaringan (direct link) tunggalDalam praktek: jaringan dibangun diatas kumpulan berbagai jenis jaringan.Dalam praktek: penulisan software (proses) yang mendukung model abstraksi “communication channel”.

Sifat:Mendukung heterogenitas jaringan: tidak bergantung pada implementasi hardware, topologi dan platform (sistem operasi, jenis nodes dll)Potensi skala konetivitas

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Basics of Internetworking

“The Internet: a specific global internetwork that grew out of ARPANET”Internet: widely used, global internetworkKita akan mendalami prinsip internetworking, dgn menggunakan Internet sbg contoh

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Heterogeneity

Routers (R1, R2..) interconnect networks of different types

R2R1

H4

H5

H3H2H1

Network 2 (Ethernet)

Network 1 (Ethernet)

H6

Network 3 (FDDI)

Network 4(point-to-point)

H7 R3 H8

FDDI: Fiber Distributed Data Interface

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Heterogeneity

Protocol stack perspective

R1

ETH FDDI

IPIP

ETH

TCP R2

FDDI PPP

IP

R3

PPP ETH

IP

H1

IP

ETH

TCP

H8

Transport Layer

Network Layer

Data Link Layer

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Internet Protocol (IP): protocol stack

Network protocol for the InternetOperates on all hosts and routers (routers are nodes connecting distinct networks into the Internet)

Ethernet FDDI ATM phone line

IP

FTP HTTP

TCP UDP

TFTP... ...

......

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The Internet Protocol: Layer

App

Transport

Network

Link

TCP / UDP

IP

DataHdr

DataHdr

TCP Segment

IP Datagram

Layer

Paket data yang dikirimkan dalam internetworking

Paket data yang dibuat oleh end-system (host)

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IP: Outline topics

Outline of internetworking with IPservice modeloverview of message transmissionhost addressing and address translationdatagram forwardingfragmentation and reassemblyerror reporting/control messagesdynamic configurationprotocol extensions through tunneling

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IP: service model

Service untuk Transport layer (TCP, UDP)global name space & identifikasi host (address)host-to-host connectivity (connectionless)“best effort” packet delivery

Not in service model: delivery guarantees on bandwidth, atau delay => DATAGRAMDelivery failure modes

packet delayed for very long timepacket lostpacket delivered more than oncepackets delivered out of order

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Message transmission

Ethernet(ETH)

FDDI

ATM

MyHostOtherHost

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Message transmission

1. MyHost (aplikasi) menggunakan IP address OtherHost utk mengirim paket

2. MyHost (IP) forwards paket IP ke Loper3. MyHost (IP) mencari alamat Ethernet dr Loper, dan mengirim frame

yang berisi paket IP untuk OtherHost4. Loper (IP) forwards paket ke OtherHost5. Loper (IP) mencari alamat FDDI dari OtherHost dan mengirim frame

FDDI yang berisi paket IP untuk OtherHost

TCP

IP

MyHost

IP

TCP

OtherHostLoper (router)

IP

FDDI FDDIETHETH

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IP (IPv4) : address model

Internet address properties32-bit addresshierarchical: network (/subnetwork), host

traditional 3-class model

0 network (7) host (24 bits)

1 0 network (14 bits) host (16 bits)

1 01 network (21 bits) host (8 bits)

A:

B:

C:

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IP Multicast

1111 + Future UseE

1110 + Multicast Address

D

221256 - 28 bit110 + 21 bitC

21465,536 - 216 bit10 + 14 bitB

126224 - 224 bit0 + 7 bitA

# of Networks

# of Addresses

Host IDNetwork IDClass Range of Host Addresses

1.0.0.0 to 127.255.255.255

128.0.0.0 to 191.255.255.255

192.0.0.0 to 223.255.255.255

224.0.0.0 to 239.255.255.255

240.0.0.0 to 255.255.255.255

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Special IP Addresses

Mengapa no of addresses class A, B, & C dikurangi 2?

Bagaimana dgn IP 255.255.255.255?

Network 111 … 111 Broadcast on a distant LANs anywhere in the Internet

Network 000 … 000 Network ID

11111111.11111111.11111111.11111111 Broadcast on the local n/w

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Special IP Addresses

Mengapa no of networks di kelas A adl 126 (27-2) & bukannya 128 (27)?

0.x.y.z digunakan utk keperluan khusus

127.x.y.z digunakan utk loopback testing

00000000.00000000.00000000.00000000 This host

00 … 00 Host A host on this n/w

01111111 Host

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IP addressesDecimal-dot notationHost in class A network

• 56.0.78.100 www.usps.govHost in class B network

• 152.118.14.3 www.cs.ui.ac.idHost in class C network

• 198.182.196.56 www.linux.org

Internet domain namesASCII strings separated by periodsProvides some administrative hierarchy

• host.sub.domain.domain_type (com, ac, …)• host.domain.country (us, de, jp, id,…)

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IPv4 Address Translation support

Misalkan: Identifikasi alamat IP host ke LAN physical addresses (i.e alamat Ethernet)Masalah:

IP addresses are not enough, because the link-layer h/w does not understand the IP addresses.Rute IP dapat melalui berbagai transit jaringan fisik yang berbeda (address berbeda).Data (paket IP) harus disampaikan ke jaringan fisik dimana host tujuan beradaHost (tujuan) hanya dapat menerima (mendengar) paket melalui physical address (network adapter/interface)

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IPv4 Address Translation support

Mekanisme: korelasi antara IP address suatu host dengan alamat fisik/hardware network adapterAddress Resolution Protocol (ARP):

Maps IP addresses to link-layer addresses, e.g. 48-bit Ethernet addresses assigned by the NIC manufacturer

Reverse Address Resolution Protocol (RARP):

Does the reversal

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IP to Physical Address Translation

Hard-codedIP address bagian host, diberikan sesuai dengan physical address (encode) dr host tsb.Jarang digunakan: sulit untuk penyesuaian dan mapping.

Fixed tableTerdapat tabel translasi yang disimpan pada suatu“central repository”Tabel didistribusikan melalui central tsb

Automatically generated tableTerdapat protokol khusus (mis. ARP) untuk membangun tabel pada setiap hostUpdate & clean-up: timeout untuk entry tabel.

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Address Resolution Protocol (ARP)

Node mengetahui apakah tujuan paket IP berada pada subnetwork yang sama (bagian network address dari IP) Memanfaatkan kemampuan “broadcast” padalink/physical layer (terutama LAN)

Protokol ARP bertugas: inquiry (broadcast) untuk mendapatkan data pasangan alamat IP dan physical address.

Setiap node akan memproses broadcast paketARP dan membandingkan IP (target) dengan IP sendiri

Jika sama => ARP response ke node originator request ARP

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Address Resolution Protocol (ARP)

Check table for physical addressIf address not present

Broadcast a query, include host’s translationWait for a response

Upon receipt of ARP query/responseTargeted host responds with address translationIf the sender’s link-level & IP addresses already present:

• Refresh entry and reset timeoutIf the address does not present

• Add entry for requesting host (if the host is the query target)• Ignore for other hosts

See slide 32

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IP: Datagram Forwarding

Properties:Setiap paket IP harus mempunyai alamat IP untuk host tujuanSetiap alamat IP mempunyai informasi host tujuan berada pada “network” yang mana (“bagian network” dari IP address)Semua host dan router yang terhubung pada satu“network” (physical) mempunyai alamat “network” yang sama dari IP address

• Misalkan: 198.192.186 (network address) => suatu jaringan LAN X; semua host yang terhubung dengan LAN X, mempunyai alamatIP: 198.192.186.xx

Pada satu “network” host2 dan router2 dapat menyampaikan paket IP langsung dengan mengirim frame menggunakan alamat fisik

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IP: Datagram Forwarding

The algorithm:If (NetworkNum of destination = NetworkNum of one of my interfaces) thendeliver packet to destination over the interface

Else• If (NetworkNum of destination is in my forwarding table)

thendeliver packet to NextHop router

• Elsedeliver packet to default router

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Forwarding: “network”

198.192.186

MyHostOtherHost

198.192.186.23

198.192.186.10

198.190.180.

198.142.100.

198.142.100.10

R1

YourHost

R5

R2

198.192.186.12

198.192.187

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Forwarding Table

Contoh Forwarding Table: Router R1

Network Address Next Hop

198.142.100 R5

198.190.180 R2

198.192.186 Interface 0

198.182.187 Interface 1

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ARP & Datagram Forwarding

[TAN03] Computer Networks 4th ed., Tanenbaum, figure 5-62

Three interconnected class C networks: 2 Ethernets & 1 FDDI ring

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Host 1 (192.31.65.7) sends to host 2 (eagle.cs.uni.edu)DNS: host name -> IP address

eagle.cs.uni.edu -> 192.31.65.5The network parts of host 1 & host 2 IP addresses show that they are on the same network

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ARP: IP address -> link-layer addressThe sender broadcast a message to the LAN “Who owns IP address 192.31.65.5?”ARP caches: the sender data link layer address is cached (with timer) for future use:

• Other hosts on the CS Ethernet can record (192.31.65.7,E1)

Ethernet address 2 (E2) will reply• Host 1 will record (192.31.65.5,E2) in its ARP cache for

future useSee slide 25

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Host 1 (192.31.65.7) sends to host 4 (192.31.63.8)Router does not forward data link layer broadcastIP addresses show the two hosts are in different networksHost 1 sends to a default Ethernet address for remote traffic (E3) at CS router

Dest Link-Level Addr =

E3

Src Link-Level Addr =

E1

Dest Addr = 192.31.63.8

(Host 4)

Src Addr = 192.31.65.7

(Host 1)… ……

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CS router:Checks its routing table:

• Packets to network 192.31.63.0 goes to router 192.31.60.7

Finds out the data link address of 192.31.60.7 (reads the ARP cache or sends ARP broadcast)Inserts the IP packet into the payload field of an FDDI frame, sends it to F3


F3


F1

Dest Addr = 192.31.63.8

(Host 4)

Src Addr = 192.31.65.7

(Host 1)… ……

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EE Router:Finds out the the data link address of 192.31.63.8 (uses ARP cache or broadcast)Builds an ethernet frame & sends it to E6

PS: link-level address = physical address = hardware address = interface address. Contohnya adl Ethernet address.


E6


E4

Dest Addr = 192.31.63.8

(Host 4)

Src Addr = 192.31.65.7

(Host 1)… ……

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Host 1 (192.31.65.7) sends to host 4 (192.31.63.8)

CS Router

E3 F1

IPIP

E1

EE Router

F3 E4

IP

H1

IP

E6

Network Layer

Data Link Layer

H4

Data Link Frame:Destination Address E3 F3 E6

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IP: service model


Not in service model: delivery guarantees on bandwidth, atau delay => DATAGRAMDelivery failure modes

packet delayed for very long timepacket lostpacket delivered more than oncepackets delivered out of order

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Review: IP service model


Identifikasi “host” pada jaringan luas:Address: potensi jumlah yang besar, dan unikDisusun secara hirarkis (analogi nomor telepon)IP address:

• Setiap host => IP address (terkait dengan network interface padahost tsb). Ingat ARP.

• Hirarkis (tidak flat): “network address” dan “host address”

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Private IP Address

RFC 1918 - IANA (Internet Assigned Numbers Authority) assigned private IP address:

10.0.0.0 to 10.255.255.255 (class A) 172.16.0.0 to 172.31.255.255 (class B)192.168.0.0 to 192.168.255.255 (class C)

Bagaimana jika host dgn private IP address perlu terhubung ke Internet?

NAT (Network Address Translation)

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NAT (Network Address Translation)

[TAN03] Computer Networks 4th ed., Tanenbaum, figure 5-60

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Public IP Address

IP public diatur oleh ICANN (The Internet Corporation for Assigned Names and Numbers)

Untuk Asia Pasifik registrasi didelegasikan melalui APNIC (http://www.apnic.net)APNIC juga memberikan porsi alokasi IP address pada NIR (National Internet Registry) dan ISP

Keterbatasan IP address:Terutama untuk kelas B

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IP Packet Size

Maksimum panjang IP datagram (header + data) adl 64 KB.

Total length of IP datagram dinyatakan dlm 16 bit, 216 = 65, 535 bytes = 64KB

Masalah:Perbedaan data link layer (variasi) yang membatasi panjang “frame” (mis. Ethernet hanya1500 bytes)

• Dikenal sebagai: Maximum Transmission Unit (MTU)Source host tidak dapat mengetahui berapaminimum MTU (protokol link yang akan dilewati)

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IP: Fragmentation and Reassembly

Solusi:Jika diharuskan: IP paket dapat dipecah(fragmentation) oleh router dalam beberapa paketIP

• Setiap paket IP dikirim pada setiap frame ke linkQuestions

• Di mana fragmen paket-paket tersebut digabung (re-assembly) kembali?

• Apa yang harus dilakukan jika salah satu fragmen hilang atau rusak?

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IP: Fragmentation and Reassembly

Fragmen adalah paket lengkap (IP datagram)Penggabungan fragmen dilakukan pada tujuan (destination address) => minimalisasi refragmentationJika satu atau lebih fragmen hilang => discard semua fragmen lainMencegah banyaknya fragmentasi:

Source host harus mengirim paket cukup kecil dalam perkiraan MTU dari “lokal” physical network.

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IP: Packet Format

Version HLen TOS LengthIdent Flags Offset

TTL Protocol ChecksumSourceAddr

DestinationAddrOptions (variable) Pad

(variable)

0 4 8 16 19 31

Data

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IP Packet Format

4-bit versionIPv4 = 4, IPv6 = 6

4-bit header lengthCounted in 32-bit words, minimum of 5

8-bit type of service field (TOS)

Mostly unused16-bit data length

Counted in bytesSee slide 7

Fragmentation support

16-bit packet ID • All fragments from the

same packet have the same ID

3-bit flags• 1-bit to mark last fragment

(more fragment or no)13-bit fragment offset into packet

• Counted in 8-byte words (64-bit units)

See slide 48

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IP Packet Format

8-bit time-to-live field (TTL)

Hop count decremented at each routerPacket is discarded if TTL = 0

8-bit protocol fieldTCP = 6, UDP = 17

16-bit IP checksum on header

32-bit source IP address32-bit destination IP addressOptions

Variable sizeSource-based routingRecord route

PaddingFill to 32-bit boundaries

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Contoh Fragmentasi

User data di fragmen pertama harus merupakan kelipatan 64 bit (8 oktet)208/8 = 26Back to slide 46?

1 byte = 1 octet = 8 bitLihat [PET00]figure 4.4.

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Internet Control Message Protocol (ICMP)

IP companion protocolHandles error and control messages

ModemATMFDDIEthernet

FTP TFTPNVHTTP

TCP UDP

IP ICMP

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ICMP Message Types

Destination unreachable: Packet could not be delivered.Time exceeded: TTL field hits 0.Parameter problem: Invalid header field.Source quench: Choke packet.Redirect: Teach a router about geography.

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ICMP Message Types

Echo request: Ask a machine if it is alive.Echo reply: Yes, I am alive.Timestamp request: Same as Echo request, but with timestamp.Timestamp reply: Same as Echo reply, but with timestamp.

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Host Configuration

Menambahkan suatu host baru ke dalam jaringan IP

Informasi apa saja yang diperlukan?Bagaimana proses tersebut dapat diotomatisasi => maintainance & trouble-shootingRemember: host sering berpindah, konfigurasi (router) berubah dst.

Some answersHost needs an IP address (must know it)Host must also

• Send packets out of physical (direct) network• Thus needs physical address of router

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Reverse Address Resolution Protocol (RARP)Translate physical address to IP address

“My 48-bit Ethernet address is 14.04.05.18.01.25. Does anybody know my IP address?”

Digunakan untuk “booting” diskless hosts (workstation)

Saat boot, host melakukan broadcast request ke semua host di jaringan (destination MAC address diberi nilai 1 semua)

RARP server memberikan informasi IP dari host tsb.Kekurangan: broadcast terbatas pd satu network, tidak di-forward oleh router

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Boot Protocol (BOOTP)

Menggunakan paket UDP UDP (transport layer): memungkinkan boot requests melalui routersIP address dari BOOTP server harus diketahuiInformasi tambahan dari BOOTP server: IP address of file server, subnet mask, and default router for hostKekurangan: network administrator harus menambahkan entri (Ethernet address, IP adrress) secara manual

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Dynamic Host Configuration Protocol (DHCP)

Cara sederhana untuk otomatisasi informasi konfigurasi (IP, router dsb)

Pengelola jaringan (administrator): centralized control untuk distribusi IP address (policy dansetup)Memungkinkan manual atau automatic IP address assigmentEfektif: jaringan yang besar dan dinamis (mis. mobile computer)Perlu server yang menjadi rujukan (DHCP server)

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Dynamic Host Configuration Protocol (DHCP)

Setiap host baru mengirim request ke DHCP server untuk IP address dan informasi lainDHCP server menerima request dari:

Langsung: jika mesin baru mempunyai IP address dariDHCP server (bagian konfigurasi OS)Broadcast: jika berada pada satu link (physical network).Via DHCP relay: nodes yang dapat melakukan forward request ke DHCP server

DHCP mampu menentukan policy pemakaian IP:Host harus melaporkan IP address yang digunakan (saat selesai boot) => tracking dan konfirmasi kembali (miripleased). Mengapa?

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DHCP

DHCP Server

Host A1. Host A

broadcasts DHCPDISCOVER

message3. Host B

broadcasts DHCP request

Host B

DHCP Relay

Other NetworksOther

Networks

4. Relay unicasts DHCP

request to server

2. Server responds with host’s IP address

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DHCP

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Virtual Networks

Goal: kontrol koneksi Konektivitas “akses” terkendali (controlled)

• Pembatasan “forwarding” hanya untuk host tertentu (authorized virtual circuit)

Pembatasan pemakaian “kapasitas”• Menentukan prioritas untuk forwarding pada router• Garansi kualitas bandwidth, delay dll.

Virtual Private NetworkSuatu kumpulan “subnets yang terhubung”Koneksi antar subnets menggunakan “shared network”, mis. internet IP networkTambahan security: penyandian data paket dsb. ReadIPsec

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Virtual Private Networks

C

A B

M

K L

C

A BM

K L

Private Networks (Traditional)Physical links (private)

usually using leased lines from the telephone companies

Virtual circuits Y (shared links)

Physical links

Virtual Private Networks

X

Y

Y

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Tunneling

IP TunnelTunnel: membungkus paket ke dalam paketVirtual point-to-point link antar dua pasang node IP (mis. R1 dan R2 => setup virtual tunnel)

Network 1

Network 1

Network 2

Network 2InternetworkInternetwork

R1 R2IP Tunnel

IP Dest = 2.xIP Payload

IP Dest = 10.0.0.110.0.0.1



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Forwarding Table

Contoh forwarding table for router R1

Network No Next Hop

1 Interface 0

2 Virtual interface 0

Default Interface 1

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Tunneling

AdvantagesTransparent transmission of packets over a heterogeneous networkOnly need to change relevant routers

DisadvantagesIncreases packet sizeProcessing time needed to encapsulate and unencapsulate packetsManagement at tunnel-aware routers

Documents

Internetworking - · PDF fileimplementasi yang berbeda pada protokol bawah ... 127.x.y.z digunakan utk loopback testing ... Src Link-Level Addr = E1 Dest Addr =