Modul 5 Gateway and Routing Protocol

1. Modul 5Gateway and Routing Protocol Mata Kuliah Sistem Telekomunikasi Semester Genap 2009 - 2010

2. Outline • Gateways, Bridges, and Routers • Gateway Protocols • Routing & Routing Daemons • The IGP and EGPGateway Protocols • Gateway-to-Gateway Protocol (GGP) • Interior Gateway Protocols (IGP) • The External Gateway Protocol (EGP)

3. Pengenalan • TCP/IP telah berkembang membentuk jaringan LAN bahkan internet dengan ribuan server dan jaringan yang kompleks terhubung satu sama lain (interworks). • Hal ini dimungkinkan dengan adanya perangkat-perangkat berbasis IP seperti Gateway, Bride, Router dll. • Penyampaian pesan dari satu komputer ke komputer membutuhkan metode routing tertentu. • Metode untuk menyampaikan informasi routing dalam jaringan sangat tergantung role network gateways. • Terdapat protokol khusus yang dikembangkan untuk berbagai macam gateway. Protocol ini bekerja bersama-sama dengan TCP.

4. Gateways, Bridges, and Routers • Gateway adalah sebuah perangkat yang menjalankan fungsi routing, biasa perangkat stand-alone yang juga menjalankan translasi protokol dari satu jaringan ke jaringan lainnya : • Kemampuan konversi protokol sangat penting biasanya terjadi di layer rendah (physical, data link, network) namun kadang-kadang termasuk layer transport. • Konversi dapat terjadi dalam berbagai bentuk, misalnya ketika paket berpindah dari format LAN ke Ethernet (terjadi perubahan format paket) atau dari sebuah file yang mempunyai konvensi proprietary ke bentuk lainnya. • Bridge adalah perangkat jaringan yang menghubungkan satu atau lebih jaringan yang menggunakan protokol yang sama. • Router adalah sebuah node jaringan yang meneruskan (forward) datagrams melalui jaringan IP.

5. Devices Kemampuan Bridge antara lain: • Semua kemampuan repeater terdapat pada Bridge. • Menghubungkan dua segmen dan regenerate signal pada level paket • Berfungsi pada Data Link Layer (melihat sinyal melalui MAC Addressnya) • Menghubungkan media fisik berbeda seperti twisted pair dengan coaxial ethernet. • Menghubungkan antar segmen jaringan berbeda seperti ethenet dan token ring. Bridge

6. Devices Hub melakukan fungsi : • Sebagai konsentrator • Pada aktif hub dapat menjadi multiport repeater • Bekerja pada layer 1 model OSI (melihat sinyal pada level bit) Hub

7. Devices Fungsi Switch : • Sebagai konsentrator • Sebagai multiport bridge • Bekerja pada layer 2 OSI (melihat sinyal melalui MAC Addressnya) Switch

8. Devices Kemampuan router antara lain: • Membagi segmen jaringan yang besar menjadi segmen yang kecil-kecil. • Memfilter dan mengisolasi trafik. • Menghubungkan segman jaringan yang berbeda topologi dan metode akses. • Dapat melalukan routing paket dengan shorthest path, dari banyak pilihan jalur. Router

9. Broadcasts Semua hub memforward semua traffic ke semua perangkat

10. Broadcasts Jadi jika Host 1 ingin melakukan ping Host 2, semua perangkat akan melihat paket ping yang dikirimkan. 1 2 Semua host akan menerima paket ping request dari host 1, tapi hanya host 2 yang akan menjawab

11. Bridge Untuk mengurangi jumlah traffik, mulai digunakan bridges untuk memfilter paket berdasar alamat MAC

12. Bridge Sekarang, jika Host 1 melakukan ping ke Host 2, maka hanya semua host dalam satu LAN segment yang melihat paket ping. Bridges stop the ping. 1 2

13. Switch Sebuah switch (multi-port bridge), secara efektif menggantikan keempat bridge yang digunakan.

14. 10 Mbps 10 Mbps The Cloud 10 Mbps 10 Mbps Switch Keungungan lain adalah, setiap LAN segment akan memperoleh dedicated bandwidth. 10 Mbps

15. Switch Sebuah switch tidak bisa menghentikan paket ping yang ditujukan pada LAN segment yang berbeda, sehingga ditujukan ke semua port dari switch. 1 1 2

16. Switch For example, Host 1 pings Host 16. Since Host 16 is on another LAN segment, the switch will flood the ping request out all ports. Perangkat apa yang bisa memperbaikinya? 1 16

17. Router Routers memfilter traffic berdasarkan alamat IP, dimana alamat IP akan memberitahu router segment mana yang harus dituju oleh paket ping. 1 1 16

18. Devices Function At Layers Jadi, dapat diambil kesimpulan, bahwa suatu perangkat tidak hanya bekerja pada layernya sendiri, tapi juga layer dibawahnya

19. Gateway Protocols

20. Gateway Protocol • Gateway protocols are used to exchange information with other gateways in a fast, reliable manner • The Internet provides two types of gateways: core and non-core • All core gateways are administered by the Internet Network Operations Center (INOC). • Non-core gatewaysare not administered by this central authority but by groups outside the Internet hierarchy • The origin of core gateways arose from the ARPANET • ARPANET called them stub gateways, • Anygateway not under direct control (non-core in Internet terms) was called a nonrouting gateway.

21. Internet from the start • First, there was ARPANET • Routers had complete information about all the possible destinations – core routers • GGP (gateway-to-gateway) protocol was used for routing – a distance vector protocol R R H R H R H CS573: Network Protocols and Standards

22. ARPANET R R Core Routers R LAN LAN LAN Internet from the start • Then, LANs were connected to ARPANET CS573: Network Protocols and Standards

23. Internet from the start • Problems with above configuration: • Routing overhead increased with the number of connected routers • Number of routes increased with the number of connected segments • Frequency of routing exchanges increased • Higher likelihood that something went wrong somewhere requiring updates • Number of different types of routers increased • Slow deployment of new versions of routing algorithms CS573: Network Protocols and Standards

24. Gateway-to-Gateway Protocol (GGP) • The move to the Internet and its proliferation of gateways required theimplementation of the Gateway-to-Gateway Protocol (GGP), which was used betweencore gateways. • The GGP was usually used to spread information about the non-coregateways attached to each core gateway, enabling routing tables to be built.

25. Interior and Exterior Gateway • As the Internet grew, it became impossible for any one gateway to hold a complete map of the entire internetwork • If the local network has more than one gateway and they can talk to each other, theyare considered interior neighbors. (The term interior neighbor is sometimes applied to themachines within the network, too, not just the gateways.) • If the gateways belong todifferent autonomous systems, they are exterior gateways. • when default routes are required, it is up to the exterior gateways to route messages between autonomoussystems. • Interior gateways are used to transfer messages into an autonomous system.

26. Interior and Exteriour Gateway Protocol • the method of transferring routing information between interiorgateways is usually the Routing Information Protocol (RIP) or the less common HELLOprotocol, both of which are Interior Gateway Protocols (IGPs). • These protocols aredesigned specifically for interior neighbors. • On the Internet, messages between twoexterior gateways are through the Exterior Gateway Protocol (EGP). • RIP, HELLO, andEGP all rely on a frequent (every thirty seconds) transfer of information betweengateways to update routing tables. • EGP is used between gateways of autonomous systems, • whereas the IGPs RIPand HELLO are used within the network itself. • GGP is used between core gateways.

27. Ilustrasi

28. Routing and Routing Daemon

29. Routing • Routing refers to the transmission of a packet of information from one machine throughanother. • Each machine that the packet enters analyzes the contents of the packetheader and decides its action based on the information within the header. • If thedestination address of the packet matches the machine's address, the packet should beretained and processed by higher-level protocols. • If the destination address doesn'tmatch the machine's, the packet is forwarded further around the network. • Forwardingcan be to the destination machine itself, or to a gateway or bridge if the packet is to leave the local network.

30. Routing (cont) • Routing is a primary contributor to the complexity of packet-switched networks. • It isnecessary to account for an optimal path from source to destination machines • It is necessary to handle problems such as • a heavy load on an intervening machine or • the loss of aconnection. • The route details are contained in a routing table • severalsophisticated algorithms work with the routing table to develop an optimal route for a packet.

31. Routing in the Internet • Routing Algorithms • Bellman-Ford • Dijkstra • Routing Protocols • Distance Vector • Link State • Routing Hierarchy • Interior Gateway Protocols (RIP, OSPF, IGRP) • Exterior Gateway Protocols (EGP, BGP, CIDR, Policy Routing) • Multicasting (IGMP) CS573: Network Protocols and Standards

32. Routing Daemon • Routing daemons initialize and dynamically maintain the kernel routing table by communicating with daemons on other systems to exchange routing information • For example, what networks are known by the machine on which the daemon is running. • Routing daemon is used to handle the routing tables : • A daemon for most UNIX systems called routed. • A few systems run a daemon called gated. • Both routed and gated can exchange RIP messages with other machines, updating their route tables as necessary. • Both routed and gated can be managed by the system administrator to select favorable routes, or to tag a route as not reliable. • The gated program can also handle EGP and HELLO messages, updating tables for the internetwork.

33. Methods of Building ARouting Table • A fixed table is created with a map of the network, which must be modified andreread every time there is a physical change anywhere on the network. • Less complex but it is inflexible and can't react to changes in the network topology quickly. • A fixed central routing table is used that is loaded from the central repositoryby the network nodes at regular intervals or when needed. • Simpler than a fixed table because it is possiblefor an administrator to maintain the single table much more easily than a table on each node. • A dynamic table is used that evaluates traffic load and messages from other nodesto refine an internal table. • It is the best for reacting to changes, although it does require bettercontrol, more complex software, and more network traffic. • Since the advantages outweigh the disadvantages, a dynamic table is the method most frequently used on the Internet.

34. Fewest-Hops Routing • Most networks and gateways to internetworks work on the assumption that the shortest route • Each machine that a message passes through is called a hop, so this routingmethod is known as fewest hops. • Although experimentation has shown that the fewesthopsmethod is not necessarily the fastest method • because it doesn't take into account transmission speed between machines • it is one of the easiest routing methods to implement.

35. Fewest-Hops Routing the tables of the gateways through which a message travels to its destination should have same route information Disadvantages : The fewest-hops method doesn't account for transfer speed, line failures, or other factors that could affect the overall time to travel to the destination

36. Type of Service Routing • This type of routing depends on the type of routing service available from gateway to gateway. • This is called type of service (TOS) routing • Also more formally called quality of service (QOS) by OSI. • TOS includes consideration for the speed and reliability of connections, as well as security and route-specific factors. • most systems use dynamic updating of tables that reflect traffic and link conditions • dynamic updating occurs at regular but not too frequent intervals • The IP header's Time to Live (TTL) field is very important to dynamic gateway routing protocols to prevent datagrams circulate throughout the network indefinitely.

37. Updating Gateway Routing Information • Gateway C has a copy of gateway A's routing table, and vice versa. • Gateways B and D each have copies of the other's routing tables, as well. • These copies are transmitted at intervals so the gateways can maintain an up-to-date picture of the connections available through the other gateway. • The gateways use EGP to send the messages. (They would use GGP if they were core gateways.)

38. Update Routing Table : EGP to GGP • Core gateways use GGP, and non-core gateways use EGP, so there must be some method for the two to communicate with each other to find out about hidden machines and networks that lie beyond their routing tables. • Gateway A is a core gateway leading from the internetwork to a network that has non-core gateways leading to two other networks. • Another gateway on the internetwork does not have information about the networks and gateways past the core gateway, unless specifically updated about them through a request.

39. IP Routing Protocols Gateway-to-Gateway Protocol GGP CS573: Network Protocols and Standards

40. GGP • The “old” ARPANET routing protocol • Defined in RFC 823 • A distance-vector routing protocol • Only core routers participate in GGP • GGP messages travel in IP datagrams with protocol type = 3 • GGP measures distance in router hops. i.e., the number of hops along a path refers to the number of routers CS573: Network Protocols and Standards

41. GGP Message Types • 4 types of GGP messages • GGP Routing Update message (type 12) • GGP Acknowledgment message (type 2/10) • GGP Echo Request or Reply (type 0 or 8) CS573: Network Protocols and Standards

42. GGP Routing Update • A router sends this message to advertise the destination networks it knows how to reach • To keep the size of message small, networks are grouped by distance • In the message “Distance” is followed by a list of “Net” addresses that are at this distance • Contains a field that tells how many distance groups are being reported (3 in case below) • D1 – Net1, Net5, Net11 • D2 – Net4, Net2, Net7, Net16 • D3 – Net6, Net9 CS573: Network Protocols and Standards

43. IGP Routing Protocols Routing Information Protocol RIP CS573: Network Protocols and Standards

44. Routing Information Protocol • A distance vector based IGP • Similar to GGP • Designed at UC Berkeley • Based on Xerox XNS • Distributed with 4BSD UNIX (routed) • First RFC was 1058, current RFC is 2453 • Started off in small networks and then extended to larger networks • See Huitema, Chapter 5 CS573: Network Protocols and Standards

45. RIP Details • Routers are active machines • Advertise their routes (IP NET, distance) to others • Hosts are passive machines • They listen and update their routes but do not advertise • RIP uses hop count metric • RIP messages are transmitted using UDP at port 520 CS573: Network Protocols and Standards

46. RIP Route Computation • There is a cost associated with each link • Typically cost =1 i.e., number of hops • Each router receives route advertisements from its neighbors • Advertisements show distances to all destinations in the network • For each destination in the network: • The router takes each received advertisement and adds to it the cost to reach that neighbor who sent this advertisement; this gives the distance to the destination • The router selects lowest of these as path/cost to that destination CS573: Network Protocols and Standards

47. Algorithm Properties • Convergence is guaranteed in a finite time given that topology remains static • Starting value of distance estimates to each destination can be any non-negative number • No assumption is made as to when the updates are sent or when the distances are computed • Each router can work based on its own clock and send its updates asynchronously • If the network changes, routes converge to a new equilibrium point CS573: Network Protocols and Standards

48. Example Advertisement: Distance to A is 2 Distance to B is 3 Distance to C is 5 Router Advertisement: Distance to A is 1 Distance to B is 4 Distance to C is 1 Cost = 1 Cost = 3 P1 P3 P2 Cost = 2 Advertisement: Distance to A is 2 Distance to B is 1 Distance to C is 3 CS573: Network Protocols and Standards

49. 1 A C 1 1 10 Target B D 1 1 From Via Dist Via Dist Via Dist Via Dist Via Dist Via Dist A B 3 C 4 C 5 C 6 C 11 C 12 B x - C 4 C 5 C 6 … C 11 C 12 C B 3 A 4 A 5 A 6 A 11 D 11 D di 1 di 1 di 1 di 1 di 1 di 1 Counting to Infinity Routes to Target: A: route via B, distance 3 B: route via D, distance 2 C: route via B, distance 3 D: direct, distance 1 Assume that B to D link goes down, and B notices. To reach target … x = destination unreachable; di = directly connected What if the link from C to D also goes down? Counting to Infinity!!! CS573: Network Protocols and Standards

50. Some Solutions • Split Horizon • If A reaches a destination through B, it makes no sense for B to reach the same destination through A • Instead of broadcasting the same distance vector on all links, send different versions on each outgoing link by removing the entries for the destinations that are reachable through that link • Split Horizon with Poisonous Reverse • Include all the destinations in advertisements; even those which were missing in split horizon, but… • Set those vector distances to infinity that were missing in the simple version of split horizon CS573: Network Protocols and Standards