Matakuliah
Tahun
Versi
: H0174/Jaringan Komputer
: 2006
: 1/0
Pertemuan 21
Internetworking
1
Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa
akan mampu :
• Menunjukkan internetworking
2
Outline Materi
• Bridge
• Router
• Switch
3
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
4
How Networks Differ
5-43
5
Internetworking Devices
Types of devices for interconnecting LAN
 Bridge
 Routers
 Layer 2 switch
 Layer 3 switch
6
Interconnecting Networks
(a) Two Ethernets connected by a switch.
(b) Two Ethernets connected by routers.
7
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)
8
Connection of Two LANs
9
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
10
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
11
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
12
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
13
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
14
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
15
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
16