Matakuliah : H0484/Jaringan Komputer
Tahun : 2007
Internetworking
Pertemuan 07
Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa
akan mampu :
• Menyediakan sambungan untuk 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) 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).
• 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 sourcedestination pair.
• Routers do all IP-level processing in
software.
• High-speed LANs and high-performance
layer 2 switches pump millions of packets
per second.
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Router
• Layer 3 switches
– Implementpacket-forwarding logic of
router in hardware
• Two categories:
– Packet by packet
– 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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