Computernetze 1 (CN1)
3 LAN Design Basics
Prof. Dr. Andreas Steffen
Institute for Internet Technologies and Applications
Steffen/Stettler, 03.10.2013, 3-LAN_Design_Basics.ppt 1
Lesestoff im Ethernet Buch
•
Kapitel 6 Ethernet Internals, Seiten 189-214
6.1 Längenbeschränkung im Ethernet
•
Kapitel 8 Ethernet-Komponenten, Seiten 275-329
8.1
8.2
8.3
8.4
•
Netzwerkkarten
Repeater und Hubs
Switches
Medienwandler
Selbststudium
Erarbeiten Sie als Vorbereitung für die Übung 4
selbständig das Thema “Spanning Tree Protocol”
mit Hilfe des Cisco Tutorials von Dan DiNicolo und
des Kapitels 4 des CN1 Foliensatzes.
Steffen/Stettler, 03.10.2013, 3-LAN_Design_Basics.ppt 2
LAN and LAN Devices
•
•
LANs make it possible for businesses that use computer technology
to efficiently share such items as files and printers and to make
possible communications such as e-mail.
LANs are designed to do the following:
•
•
•
•
operate within a limited geographic area or building
allow many users to access high-bandwidth media
provide full time connectivity to local services
connect physically adjacent devices
Steffen/Stettler, 03.10.2013, 3-LAN_Design_Basics.ppt 3
The Beginning of LAN Design
•
•
•
Initial idea: shared media LAN
Bus structure; CSMA/CD was access method
Coax cable; transmission rate up to 10 Mbit/s, half-duplex
Steffen/Stettler, 03.10.2013, 3-LAN_Design_Basics.ppt 4
Repeater
Steffen/Stettler, 03.10.2013, 3-LAN_Design_Basics.ppt 5
Repeater
•
The purpose of a repeater is to amplify and
retime network signals at the bit level.
•
Repeaters can be single-port "in" and singleport "out" devices, though more often now,
they are stackable (modular), or multi-port
repeaters, better known as hubs.
•
Repeaters are classified as layer 1 devices, in
the OSI model, because they act only on the
bit level and look at no other information.
Steffen/Stettler, 03.10.2013, 3-LAN_Design_Basics.ppt 6
Hub
•
Used in 10BASE-T and 100BASE-T networks
•
Is equivalent to a multi-port repeater
•
Hubs come in three basic types:
• passive – no traffic and signal manipulation, used only to
share the media
• active – amplifies the incoming signal
• intelligent – (smart hub) same function as an active hub,
additionally includes a controller chip and diagnostic capabilities
Steffen/Stettler, 03.10.2013, 3-LAN_Design_Basics.ppt 7
Ethernet Strukturierung
Collision Domain
single Segment
Multiport Repeater
(Concentrator, Hub)
Collision Domain
Hub
simple Repeater
Collision Domain
Collision Domain
Steffen/Stettler, 03.10.2013, 3-LAN_Design_Basics.ppt 8
Bridge
•
The purpose of a bridge is to filter traffic on
a LAN, to keep local traffic local, yet allows
connectivity to other parts (segments) of the
LAN for traffic that has been directed there.
•
The bridge makes its decisions based on
MAC addresses.
•
The bridge is a layer 2 device.
Steffen/Stettler, 03.10.2013, 3-LAN_Design_Basics.ppt 9
MAC Layer Bridge (Transparent Bridge)
Higher
Higher
MAC Layer
Bridge
MAC
DATA
MAC Sublayer
MAC
Physical Physical
Layer
Layer
Physical
Layer
X
LLC Sublayer
DA
Table
(Forwarding
Database)
SA
DA
DATA
SA
MAC Sublayer
FC S
LLC Sublayer
Layers
FC S
Layers
Port1
LAN-Segment “1”
Y
Z
Physical
Layer
Port2
LAN-Segment “2”
C
A
B
Steffen/Stettler, 03.10.2013, 3-LAN_Design_Basics.ppt 10
Bridge: Flooding or Filtering (destination address)
Error-free frame received on port x
no
Destination
address found in forwarding
database?
Forward frame
to all ports
(except port x)
Flooding
no
Forward frame
to port y
yes
Is destination again
on port x?
Filtering
yes
Discard
frame
1
Steffen/Stettler, 03.10.2013, 3-LAN_Design_Basics.ppt 11
Bridge: Learning (source address)
1
no
Source address
found in forwarding
database?
Add address with port
and age value to the
forwarding database
yes
Update port
and age value
Learning
end
Typical address aging value: 300 s
Steffen/Stettler, 03.10.2013, 3-LAN_Design_Basics.ppt 12
Learning / Flooding
SA DA
data A F L2
data A F L2
LAN 1
p1
MAC A
p2
LAN 3
learn A
MAC F
bridge 1
MAC B
MAC C
p1
learn A
LAN 2
p1
A
p2
data A F L2
MAC G
bridge 2
p2
flood F
table of bridge 1
flood F
table of bridge 2
p1
p2
A
Steffen/Stettler, 03.10.2013, 3-LAN_Design_Basics.ppt 13
Learning / Filtering
DA SA
L2 A F data
LAN 1
p1
MAC A
p2
LAN 3
learn F
MAC F
bridge 1
MAC B
MAC C
p1
MAC G
bridge 2
p2
filter A
LAN 2
table of bridge 1
p1
A
p2
table of bridge 2
p1
p2
A
F
Steffen/Stettler, 03.10.2013, 3-LAN_Design_Basics.ppt 14
Learning / Flooding
DA SA
data F G L2
L2 G F data
LAN 1
p1
MAC A
p2
LAN 3
MAC F
bridge 1
MAC B
MAC C
p1
learn F
LAN 2
p1
p2
MAC G
bridge 2
p2
flood G
table of bridge 1
flood G
data F G L2
table of bridge 2
p1
p2
A
A
F
F
Steffen/Stettler, 03.10.2013, 3-LAN_Design_Basics.ppt 15
Learning / Forwarding
DA SA
data G F L2
L2 F G data
LAN 1
MAC A
p1
LAN 3
forward F
MAC F
bridge 1
p2
learn G
table of bridge 1
MAC B
MAC C
p1
p2
learn G
MAC G
bridge 2
forward F
LAN 2
L2 F G data
table of bridge 2
p1
p2
p1
p2
A
G
G
A
F
F
Steffen/Stettler, 03.10.2013, 3-LAN_Design_Basics.ppt 16
Segmentation with Bridges
•
Bridges split a LAN into several workgroups with smaller collision
domains -> reduces whole LAN traffic
•
One "broadcast domain"
half-duplex collision domains
Steffen/Stettler, 03.10.2013, 3-LAN_Design_Basics.ppt 17
Switch
•
The purpose of a switch is to concentrate
connectivity, while guaranteeing bandwidth.
•
It switches packets from incoming ports
(interfaces) to outgoing ports, while
providing each port with full bandwidth.
•
The switch uses the MAC address to make its
switching decisions. You might think of each
port on a switch as a micro-bridge, which
makes it a layer 2 device.
Steffen/Stettler, 03.10.2013, 3-LAN_Design_Basics.ppt 18
Ethernet Strukturierung
Broadcast Domain (IP-Subnet)
(simple) Bridge
Broadcast Domain
Bridges and Backbone
Broadcast Domain
Multiport Bridge
Broadcast Domain
Steffen/Stettler, 03.10.2013, 3-LAN_Design_Basics.ppt 19
Switch Forwarding Principles
Store-and-Forward
Fast-Forward
Cut-Through
Early-Cut
6B
6B
2B
Destination
Address
Source
Address
Length
(E-Type)
0 (46)…1500B
LLC PDU
4B
Frame
Check
Sequence
6B = 4,8s *
12B = 9,6s
64B = 51,2s
1518B = 1,2144ms
* delays computed for 10 Mbit Ethernet
Steffen/Stettler, 03.10.2013, 3-LAN_Design_Basics.ppt 20
Switch Forwarding Principles
•
Early-Cut
•
• only usable when finished
• detects runts and collisions
• forwards nearly all
• can filter specific Ethertypes
learning
faulty frames
•
Fast-Forward (Fragment Free)
Cut-Through
•
Store-and-Forward
• reads destination and
• detects CRC-errors
• forwards many
• can do filtering based on
source address
faulty frames
higher-layer Information
Steffen/Stettler, 03.10.2013, 3-LAN_Design_Basics.ppt 21
Switching Fabric
Port 1
Port 2
Port 0
Port 3
cross-connect any two switch ports
Steffen/Stettler, 03.10.2013, 3-LAN_Design_Basics.ppt 22
Non-Blocking Switching Fabric
10 Gbps
10 Gbps
10 Gbps
60 Gbps Fabric
10 Gbps
Bandwidth of Fabric > Ingress + Egress
Steffen/Stettler, 03.10.2013, 3-LAN_Design_Basics.ppt 23
Blocking Switching Fabric
10 Gbps
10 Gbps
10 Gbps
20 Gbps Fabric
10 Gbps
Bandwidth of Fabric < Ingress + Egress
Steffen/Stettler, 03.10.2013, 3-LAN_Design_Basics.ppt 24
Shared Memory Architecture
General Purpose CPU
(CISC older or RISC newer)
CPU
Forwarding Tables
Buffers
Queues
Pointers
Headers
Packet
Memory
IOS Image/Files
System Buffers
CPU
Memory
Interface
Interface
Interface
Interface
Interface
Interface
Physical Media
Interfaces
(Fixed or Modular)
Interface
Processor Queues
Data/Address/
Control Buses
Steffen/Stettler, 03.10.2013, 3-LAN_Design_Basics.ppt 25
Cross Bar Switch Architecture
CPU Memory
(DRAM)
(C) Forwarding
Table
CPU
•
•
•
Multiple conflict free paths
Tx
Packet Memory
Typically higher bandwidth
Rx
(D) FT
Signaling and scheduling
is more complex
Tx
Packet Memory
Rx
(D) FT
CPU
CPU
Packet Memory
Tx
(D) FT
CPU
Packet Memory
Rx
(D) FT
CPU
Interface
Card
Interface
Card
Interface
Card
Interface
Card
Cross Bar ASIC
Steffen/Stettler, 03.10.2013, 3-LAN_Design_Basics.ppt 26
Router
•
The purpose of a router is to examine
incoming packets, choose the best path for
them through the network, and then switch
them to the proper port.
•
Routers make their path selection decisions
based on layer 3 information - the network
addresses therefore they are considered
layer 3 devices.
•
Routers can connect different layer 2 technologies, such as Ethernet, Token-ring, or
FDDI.
Steffen/Stettler, 03.10.2013, 3-LAN_Design_Basics.ppt 27