internetworking pertemuan 07 matakuliah: h0484/jaringan komputer tahun: 2007
TRANSCRIPT
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Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa akan mampu :
• Menyediakan sambungan untuk internetworking
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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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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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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.
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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