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Pertemuan 21Internetworking

Matakuliah : H0174/Jaringan Komputer

Tahun : 2006

Versi : 1/0

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Learning Outcomes

Pada akhir pertemuan ini, diharapkan mahasiswa akan mampu :

• Menunjukkan internetworking

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Outline Materi

• Bridge• Router• Switch

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Internetworking Terms

• End System (ES)– Device attached to one of the networks of an

internet– Supports end-user applications or services

• Intermediate System (IS)– Device used to connect two networks– Permits communication between end systems

attached to different networks

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How Networks Differ

5-43

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Internetworking Devices

Types of devices for interconnecting LAN Bridge Routers Layer 2 switch Layer 3 switch

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Interconnecting Networks

(a) Two Ethernets connected by a switch.

(b) Two Ethernets connected by routers.

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Internetworking Components

• Bridge– IS (Intermediate System) used to connect two

LANs using similar LAN protocols to expand beyond single LAN

– Address filtering- passing on packets to the required network only

– OSI layer 2 (Data Link)– Bridge is simple, minimal processing

• Router– Connects two (possibly dissimilar) networks– Uses internet protocol present in each router

and end system– OSI Layer 3 (Network)

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Connection of Two LANs

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Functions of a Bridge

• Read all frames transmitted on one LAN and accept those address to any station on the other LAN

• Using MAC protocol for second LAN, retransmit each frame

• No modification to content or format of frame, no encapsulation (Exact bitwise copy of frame)

• May be more than one bridge to cross• May connect more than two LANs• Bridging is transparent to stations

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Bridge Protocol Architecture

• MAC level – Station address is at this level

• Bridge does not need LLC layer– It is relaying MAC frames

• Can pass frame over external communication system WAN link– Capture frame– Encapsulate it– Forward it across link– Remove encapsulation and forward over

LAN link

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Address Learning

• Preload forwarding address database• Learn forwarding address– When frame arrives at port X, it has come from

the LAN attached to port X– Use the source address to update forwarding

database for port X to include that address– Timer on each entry in database– Each time frame arrives, source address

checked against forwarding database

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Spanning Tree Algorithm

• Address learning works for tree layout– i.e. no closed loops

• For any connected graph there is a spanning tree that maintains connectivity but contains no closed loops

• Each bridge assigned unique identifier• Exchange between bridges to establish

spanning tree

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Router

• Complex large LANs need alternative routes– Load balancing– Fault tolerance

• Routing selected for each source-destination pair • Routers do all IP-level processing in software• High-speed LANs and high-performance layer 2

switches pump millions of packets per second• Layer 3 switches– Implementpacket-forwarding logic of router in

hardware• Two categories: Packet by packet and Flow base

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Problems with Routers

• Routers do all IP-level processing in software– High-speed LANs and high-performance layer

2 switches pump millions of packets per second

– Software-based router only able to handle well under a million packets per second

• Solution: layer 3 switches– Implement packet-forwarding logic of router in

hardware• Two categories– Packet by packet – Flow based

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Layer 3 Switch

• Packet by Packet– Operates insame way as traditional router– Order of magnitude increase in performance

• Flow-based switch– Tries to enhance performance by identifying

flows of IP packets of same source and destination

– Done by observing ongoing traffic– Once flow is identified, predefined route can

be established