NETWORK LAYER : Fungsi dan Routing

Fungsi network layer Membawa paket dari host pengirim ke penerima Protokol network layer ada di setiap host dan router Tiga fungsi utama: path determination: menentukan rute yang ditempuh paket dari sumber ke tujuan (Routing algorithms) switching: memindahkan paket dari input router ke output router call setup: beberapa arsitektur jaringan mensyaratkan router call setup sepanjang jalur sebelum data dialirkan application transport network data link physical network data link physical

Protokol yang diimplementasikan pada Lapis 3: Internet Protocol version 4 (IPv4) Internet Protocol version 6 (IPv6) Novell NetWare Internetwork Packet Exchange (IPX) AppleTalk It is an OSI Network Layer service that (unlike CONS) does not require a circuit to be established before data is transmitted. CLNS routes messages to their destinations independently of any other messages. In an OSI protocol deployment, CLNS would be the service provided by CLNP (Connectionless Network Protocol) and used by TP4 (Transport Protocol Class 4). However CLNP is not used on the Internet, instead its function is provided by IP. CLNP is still widely used today in many telecommunications networks around the world. This is because IS-IS (an OSI layer 3 protocol) is mandated by the ITU-T as the protocol for management of the SDH (Synchronous Digital Hierarchy) elements. CLNP uses IS-IS (developed by DEC) for routing. CLNP type supports two values; 1 and 28. 1 is used to indicate Error Report. All the other packets use the value 28 (Hex 0x1c) (TP4, TARP). CLNP does not have a Protocol field like IP. The NSEL field in the NSAP is used for forwarding to the appropriate protocol handler. In IP it is always assumed that the end detecting and handling errors in the packet will send an error packet (via ICMP) back to the source. CLNP PDUs (PDUs are the OSI equivalent of packets) will only elicit error reports if the Error Report Requested flag is set. The CLNP header does not require the messages to be padded to the nearest 32 bit boundary. The length of a CLNP header can go up to 254 octets.

Goal: menentukan suatu jalur yang “baik” Routing Routing protocol A E D C B F 2 1 3 5 Goal: menentukan suatu jalur yang “baik” (router-router yang berurutan) melalui suatu jaringan dari source kedestination. Graph abstraction untuk algoritma routing : graph nodes (vertex) adalah routers graph edges (arc) adalah link fisik link cost Vertex = node Jalur yang “baik” : Biasanya berarti jalur dengan biaya yang minimum Bisa jadi ada definisi lain

Pergantian rute berlangsung lambat (dilakukan administrator) Dynamic: Static or dynamic? Static: Pergantian rute berlangsung lambat (dilakukan administrator) Dynamic: Rute berganti lebih cepat Update secara periodik Respon bila cost link berubah Static diatur oleh manusia/operator/administrator Dynamic diatur oleh software

Inter & Intra domain Inter Domain : BGP (antar AS) Intra Domain : OSPF, RIP, IGRP (didalam AS) Forouzan page 659, 676 AS = Autonomous System BGP = Border Gateway Protocol OSPF = Open Shortest Path First RIP = Routing Information Protocol IGRP = Interior Gateway Routing Protocol

Autonomous systems Autonomous systems divide up the global internetwork into manageable units Forouzan page 659 Autonomous systems is : a group of networks and routers under the authority of a single administration.

S Ward Abingdon and Witney College Interior and Exterior BGP used between BGP used between RIP in AS 62 EIGRP in AS 36 OSPF in AS 98 Forouzan page 659 18-Sep-18 S Ward Abingdon and Witney College

Routing Algorithm classification Global or decentralized information? Global: Semua routers mempunyai informasi yang lengkap mengenai topologi dan biaya link. “link state” algorithms (OSPF dan IS-IS) Decentralized: router hanya mengetahui perangkat yang terhubung kepadanya secara fisik serta biayanya. Proses komputasi yang iteratif dan pertukaran informasi dengan tetangganya. “distance vector” algorithms (RIP, IGRP and EIGRP) Algoritma Link State = algoritma Dijkstra = algoritma Shortest Path First IS-IS = Intermediate System to Intermediate System protocol OSPF = Open Shortest Path First RIP = Routing Information Protocol IGRP = Interior Gateway Routing Protocol EIGRP = Enhanced Interior Gateway Routing Protocol

Metric (cost) yang bisa digunakan : Hop count Bandwidth Delay Load Reliability BER Maximum transmission unit

Load balancing R 192.168.6.0/24 [120/1] via 192.168.2.1, 00:00:24, Serial0/0/0 [120/1] via 192.168.4.1, 00:00:26, Serial0/0/1 Routing table lists two routes to the same destination, with the same metric. Both routes were discovered by the same protocol. Both routes will be used.

Distance Vector Algoritma beroperasi dengan memaintain tabel routing dari setiap router . Tabel routing diupdate secara periodik. Pada lingkungan pure distance vector, update routing secara periodic melibatkan pengiriman routing table tetangga secara full. Forouzan page 660

Problem Forouzan page 663

PROBLEM count-to-infinity  Jika misal ruter A down. B tidak “mendengar” apapun dari A. Namun C “mengatakan” bahwa mengirim paket ke A bisa lewat C. dst... Solusi  tetapkan nilai maximum Routing loop  solusi : split horizon (tidak mengirimkan informasi kembali ke pengirim) Update message yang tidak perlu solusi : holddown timer

Link State Pada link state, router melakukan: Mempelajari network address dari tetangga Menghitung delay atau cost setiap tetangga Membentuk paket utk menyebarkan informasi ruting yang baru dipelajari Mengirim paket pada tiap router Menghitung shortest path ke tiap router. Paket link state (link state advertisement – LSA) identitas sender, sequence number, age Link state mengumpulkan informasi dari seluruh router dalam jaringan atau dalam area tertentu dan kemudian setiap router menghitung path terbaiknya secara independen. Jika terjadi failure, dikirimkan LSA. Masing-masing router akan mengcopy LSA, mengupdate databasenya, dan memforward database tersebut ke tetangganya. LSA menyebabkan rouer melakukan perhitungan kembali best path nya. Forouzan page 666

Forouzan page 666

Contoh link-state network hierarchi: Area : grouping of contiguous network AS : sejumlah network dalam administrasi yang sama yang men-share strategi routing yang sama. Misal di OSPF : area bacbone, area border router, nonbackbone internal router, Misal di IS-IS :router L2, L1/L2, L1

Link State Algorithm DX(Y,Z) = jarak dari X ke Y, melalui Z sebagai hop selanjutnya = c(X,Z) + minwZ{D (Y,w)}

S Ward Abingdon and Witney College Routing protocols Interior gateway protocols Exterior gateway protocols Classful Classless IPv6 18-Sep-18 S Ward Abingdon and Witney College

S Ward Abingdon and Witney College Routing protocols Interior gateway protocols Exterior gateway protocols Classful Classless IPv6 Distance vector, open standard 18-Sep-18 S Ward Abingdon and Witney College

S Ward Abingdon and Witney College Routing protocols Interior gateway protocols Exterior gateway protocols Classful Classless IPv6 Distance vector, Cisco proprietary 18-Sep-18 S Ward Abingdon and Witney College

S Ward Abingdon and Witney College Routing protocols Interior gateway protocols Exterior gateway protocols Classful Classless IPv6 Link state 18-Sep-18 S Ward Abingdon and Witney College

Administrative distance Different routes could be found by different routing protocols, or one route could be dynamic and one static. The route with the lowest administrative distance is used. Administrative distance is an indication of the “trustworthiness” or desirability of a route. 18-Sep-18 S Ward Abingdon and Witney College

Administrative distances 0 directly connected 1 static route 90 route found using EIGRP 100 route found using IGRP 110 route found using OSPF 120 route found using RIP Maximum possible value is 255 These are default values. 18-Sep-18 S Ward Abingdon and Witney College

Administrative distance D 192.168.6.0/24 [90/2172416] via 192.168.2.1, 00:00:24, Serial0/0 R 192.168.8.0/24 [120/1] via 192.168.3.1, 00:00:20, Serial0/1 Two routing protocols running on a router linking two areas with the different protocols Administrative distances are the defaults for the routing protocols. D means EIGRP. Note the metric is not hop count. 18-Sep-18 S Ward Abingdon and Witney College

SEKIAN

Algoritma Distance Vector Pada semua node,X: Inisialisasi Untuk semua node bersebelahan v DX(*,v) = ∞ {* berarti untuk semua baris} DX(v,v) = c(X,v) Untuk semua tujuan, y Kirim minwXD (y,w) kesetiap tetangga loop tunggu (sampai ada perubahan cost link ke tetangga V atau diterima update dari tetangga V) If (c(X,V) berubah dengan d) then untuk semua tujuan y: DX(y,V) = DX(y,V) + d Else if (diterima update dari V dengan tujuan Y) then untuk tujuan tunggal y: DX(Y,V) = c(X,V) + nilai baru IF ada nilai baru minwDX(Y,w) untuk semua tujuan Y then kirim nilai baru minwDX(Y,w) ke semua tetangga terus menerus