internetworking livello iii prof. alfio lombardo
TRANSCRIPT
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Internetworking livello III
Prof. Alfio Lombardo
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Il sistema Internet: Architettura protocollare
IP
network interface
IP
network interface
application
transport
IP
network interface
rete 1 rete 3
application
transport
IP
network interface
rete 2
Router Router
Host A Host B
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NODO
NODO
NODO
NODO
CIRCUITO VIRTUALE
Protocolli di rete orientati alla connessione (virtual circuit switching: esempio X.25)
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DATAGRAM
Nodo
Nodo
Nodo
Nodo D
A
B
C
Protocolli di rete orientati al datagramma (datagram switching:
esempio IP)
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Servizi di Rete Connectionlesstrasferimento di piccole quantità di dati in tempi limitati
robustezza e flessibilità dei path
efficienza nell'uso delle risorse di rete
necessità di controllo del traffico offerto dalla sorgente
processamento durante il trasferimento dei dati
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Componenti funzionali routing IP
Componente Componente DatiDati
Protocollo di Routing IPProtocollo di Routing IP Scambio delle informazioni di routing con gli altri router
Componente di Componente di ControlloControllo
Creazione e aggiornamento delle tabelle di lookup
Tabella di Routing IPTabella di Routing IP
Pacchetti uscenti
Pacchetti entranti
Decisione di Instradamento
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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
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151.97.3.4
151.97.3.4
Instradamento
router
router router
151.97.3.4
? 151.97.3.4
151.97.3.4
151.97.3.4
? 151.97.3.4
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Per inviare a Instrada verso
20.0.0.0 direct delivery
30.0.0.0 direct delivery
40.0.0.0 30.0.0.7
10.0.0.0 20.0.0.5
Routing table router R
Attraverso l’interfaccia
20.0.0.6
30.0.0.7
30.0.0.7
20.0.0.6
Tabelle di routing: statiche dinamiche
algoritmi isolati
algoritmi centralizzati
algoritmi distribuiti
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Tabella di routingP1# show ip routeCodes: 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 masksO 172.16.23.0/24 [110/128] via 172.16.13.3, 5d00h, Serial0/1C 172.16.12.0/24 is directly connected, Serial0/0C 172.16.13.0/24 is directly connected, Serial0/1C 172.16.1.0/24 is directly connected, FastEthernet0/0O IA 172.16.2.0/24 [110/74] via 172.16.12.2, 5d00h, Serial0/0O IA 172.16.3.0/24 [110/74] via 172.16.13.3, 5d00h, Serial0/1 192.168.0.0/32 is subnetted, 9 subnetsO 192.168.0.12 [110/11] via 172.16.1.12, 5d01h, FastEthernet0/0C 192.168.0.1 is directly connected, Loopback0O 192.168.0.2 [110/65] via 172.16.12.2, 5d00h, Serial0/0O 192.168.0.3 [110/65] via 172.16.13.3, 5d00h, Serial0/1O IA 192.168.0.31 [110/75] via 172.16.13.3, 5d00h, Serial0/1O IA 192.168.0.21 [110/75] via 172.16.12.2, 5d00h, Serial0/0
Destinazione Next-Hop Interfaccia di uscitaMetrica IGPDistanza amministrativa
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Address Boundary
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Ma non sempre e’ cosi’:IPv6 Base Header Format
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IPv6Addressing Model
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.
IPv6 Addresses of all types are assigned to interfaces, not nodes
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.
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- 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
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More specific prefix preferred over lessspecific prefix
example: packet with destination of 10.1.1.1is sent to the router announcing 10.1/16 ratherthan the router announcing 10/8.
“Longest match” routing
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Architetture di routing:
la circolazione stradale!
C
D E
F
G
HA
B
A,B
G,H,E,F
C,D
A
B
Altre
dir
C
D
Altre dir
C,D
G,H
,B,A
E,F
F
E
Altre dir
E,FA,B,C,D
G,H
G,H
C,D
,E,F
A,B
H
G
Altre dir
Architettura gerarchica:I livelloII livello……….
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MR 215
Routing gerarchico
R
RR R
R
R
R
R
Area 1
Area 3
Area 2
R
R
R Border arearouter (livello 2)
R Internal arearouter (livello 1)
R
R
RR
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R4
Area2
Area1:backbone
BorderRouter
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MR 216
Dominio di routing
Dominio AR R
Dominio BR R
RR
RR
Dominio C
R
R
R
R
R
RIP
OSPF
IGRP
R
RR
Dominio D
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MR 217
Autonomous System
AutonomusSystem
Dominio AR R
Dominio BR R
RR
RR
Dominio C
R
R
R
R
R
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
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Autonomous System Number (ASN)
• An ASN is a 16 bit number1-64511 are assigned by the RIRs64512-65534 are for private use and should never appear onthe Internet0 and 65535 are reserved• 32 bit ASNs are coming soonwww.ietf.org/internet-drafts/draft-ietf-idr-as4bytes-07.txt• ASNs are distributed by the Regional Internet RegistriesCurrent ASN allocations up to 32767 have been made to theRIRs
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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
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MR 218
EGP e I GP
AS3
AS1
AS2
R
Dominio A
R RDominio B
R R
R
R
R
R
R
R R
R
RR
R
R
R
R
IGPEGP
No defaultrouter
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Router
n.1
(Partial core)
Router
n.2
(Partial core)
Default route
to sites beyond
AS 2
Default route
to sites beyond
AS 1
Default route
from sites
behind AS 1Default route
from sites
behind AS 2
Esempio di Architettura fisica
del sistema di routing
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AS1: Backbone serviceProvider (core system)
AS2: ISP
AS3: piccola azienda
AS4: grande azienda
ASn:..
Internet Structure: yesterday
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AS1: Backbone serviceProvider (core system)
AS..: IPS
AS..: piccola azienda
AS4: grande azienda
ASn: ISP..
Internet Structure: today
AS..:grande azienda