Matakuliah : H0484/Jaringan Komputer
Tahun
: 2007
Internetworking
Pertemuan 22
Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa
akan mampu :
• Menjelaskan 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
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