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Internetworking livello III

Internetworking livello III. Prof. Alfio Lombardo. Il sistema Internet: Architettura protocollare. Host A. Host B. application. application. transport. transport. Router. Router. IP. IP. IP. IP. network interface. network interface. network interface. network interface.

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Internetworking livello III

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  1. Internetworking livello III Prof. Alfio Lombardo

  2. Il sistema Internet: Architettura protocollare Host A Host B application application transport transport Router Router IP IP IP IP network interface network interface network interface network interface rete 2 rete 3 rete 1

  3. Protocolli di rete orientati alla connessione (virtual circuit switching: esempio X.25) NODO NODO NODO NODO CIRCUITO VIRTUALE

  4. A C D B Protocolli di rete orientati al datagramma (datagram switching: esempio IP) Nodo Nodo Nodo Nodo DATAGRAM

  5. trasferimento di piccole quantità di dati in tempi limitati robustezza e flessibilità dei path efficienza nell'uso delle risorse di rete processamento durante il trasferimento dei dati necessità di controllo del traffico offerto dalla sorgente Servizi di Rete Connectionless

  6. Scambio delle informazioni di routing con gli altri router Protocollo di Routing IP Creazione e aggiornamento delle tabelle di lookup Tabella di Routing IP Componenti funzionali routing IP Componente di Controllo Decisione di Instradamento Pacchetti entranti Pacchetti uscenti Componente Dati

  7. Modalità di Instradamento • Direct delivery: sorgente e destinazione sono direttamente • connesse alla stessa sottorete; non coinvolge routers • Indirect delivery: sorgente e destinazione non sono • connesse alla stessa sottorete, coinvolge routers

  8. 151.97.3.4 151.97.3.4 ? ? 151.97.3.4 151.97.3.4 router router router 151.97.3.4 151.97.3.4 Instradamento 151.97.3.4

  9. Per inviare a Instrada verso Attraverso l’interfaccia 20.0.0.0 direct delivery 20.0.0.6 30.0.0.0 direct delivery 30.0.0.7 10.0.0.0 20.0.0.5 20.0.0.6 algoritmi isolati 40.0.0.0 30.0.0.7 30.0.0.7 algoritmi centralizzati Routing table router R algoritmi distribuiti Tabelle di routing: statiche dinamiche

  10. Tabella di routing P1# show ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area * - candidate default, U - per-user static route, o - ODR P - periodic downloaded static route Gateway of last resort is not set 172.16.0.0/16 is variably subnetted, 8 subnets, 2 masks O 172.16.23.0/24 [110/128] via 172.16.13.3, 5d00h, Serial0/1 C 172.16.12.0/24 is directly connected, Serial0/0 C 172.16.13.0/24 is directly connected, Serial0/1 C 172.16.1.0/24 is directly connected, FastEthernet0/0 O IA 172.16.2.0/24 [110/74] via 172.16.12.2, 5d00h, Serial0/0 O IA 172.16.3.0/24 [110/74] via 172.16.13.3, 5d00h, Serial0/1 192.168.0.0/32 is subnetted, 9 subnets O 192.168.0.12 [110/11] via 172.16.1.12, 5d01h, FastEthernet0/0 C 192.168.0.1 is directly connected, Loopback0 O 192.168.0.2 [110/65] via 172.16.12.2, 5d00h, Serial0/0 O 192.168.0.3 [110/65] via 172.16.13.3, 5d00h, Serial0/1 O IA 192.168.0.31 [110/75] via 172.16.13.3, 5d00h, Serial0/1 O IA 192.168.0.21 [110/75] via 172.16.12.2, 5d00h, Serial0/0 Distanza amministrativa Destinazione Interfaccia di uscita Metrica IGP Next-Hop

  11. Address Boundary

  12. Ma non sempre e’ cosi’:IPv6 Base Header Format

  13. IPv6Addressing Model IPv6 Addresses of all types are assigned to interfaces, not nodes An example of a Unicast address format | 128 - 48 bits | 48 bits | +--------------------------------+-----------+--------------------+ | subnet ID | interface ID | +--------------------------------+-----------+--------------------+ Where the 48-bit Interface ID is an IEEE-802 MAC address. Auto- configuration of addresses: A node may discover a subnet ID by listening messages sent by a router on its attached link(s), and then fabricating an IPv6 address for itself by using its IEEE MAC address as the interface ID on that subnet.

  14. - RouteDatagram(Datagram, RoutingTable) - Extract destination IP address, D, from the datagram and compute the network prefix, N; if N matches any directly connected network address deliver datagram to destination D over that network (This involes resolving D to a physical address, encapsulating the datagram and sending the frame) else if the table contains a host-specific route for D send datagram to next-hop specified in table else if the table contains a route for network N send datagram to next-hop specified in table else if the table contains a default route send datagram to the default router specified in table else declare a routing error; IP routing algorithm

  15. “Longest match” routing More specific prefix preferred over less specific prefix example: packet with destination of 10.1.1.1 is sent to the router announcing 10.1/16 rather than the router announcing 10/8.

  16. Architetture di routing: la circolazione stradale! D E D E C Altre dir Altre dir F C F C,D E,F A,B,C,D E,F G,H,B,A G,H C,D C,D,E,F G,H,E,F A,B Altre dir G Altre dir G,H A,B G B H Architettura gerarchica: I livello II livello ………. H A B A

  17. Area1:backbone Border Router Area2 R4

  18. Dominio D R R R

  19. Autonomous System (AS) è una porzione di rete amministrata da un unico gestore o comunque da un gruppo di persone che decidono una particolare ‘politica di routing’ per lo scambio di informazioni di routing con il resto della rete

  20. Autonomous System Number (ASN) • An ASN is a 16 bit number 1-64511 are assigned by the RIRs 64512-65534 are for private use and should never appear on the Internet 0 and 65535 are reserved • 32 bit ASNs are coming soon www.ietf.org/internet-drafts/draft-ietf-idr-as4bytes-07.txt • ASNs are distributed by the Regional Internet Registries Current ASN allocations up to 32767 have been made to the RIRs

  21. Tipi di AS • STUB: Un AS che ha un singolo punto di accesso a Internet; non ha bisogno di partecipare alla diffusione di messaggi di routing (BGP) • Non transit: un AS multi-homed che non permette traffico di transito • Transit: un AS multi-homed che permette traffico di transito

  22. No default router

  23. Default route to sites beyond AS 1 Default route to sites beyond AS 2 Esempio di Architettura fisica del sistema di routing Router n.1 (Partial core) Router n.2 (Partial core) Default route from sites behind AS 1 Default route from sites behind AS 2

  24. Internet Structure: yesterday AS1: Backbone service Provider (core system) ASn:.. AS2: ISP AS4: grande azienda AS3: piccola azienda

  25. Internet Structure: today AS..:grande azienda AS1: Backbone service Provider (core system) ASn: ISP.. AS..: IPS AS4: grande azienda AS..: piccola azienda

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