network enterprise

EE4718: Enterprise Network Design

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EE4718 Enterprise Network Design Project Page. 1

Unit 3

Enterprise Network Technology Design


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Outline

A Big Picture of Enterprise Network

Identifying and Selecting Internetworking Devices

LAN and WAN Design

Enterprise Network Design Model

Sever Placement


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A Big Picture of Enterprise NetworkEnterprise internetwork: a corporation, agency, school, or other organization that ties

together its data, communication, computing, and file servers.


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A Big Picture of Enterprise Network(contd)

Large internetworks consist of the following three distinct components:- Campus networks, which consist of locally connected users in a building or

group of buildings, i.e., Local-area networks (LANs)

- Wide-area networks (WANs), which connect campuses together

- Remote connections, which link branch offices and single users (mobile users and/or telecommuters) to a local campus or the Internet

Developments on the enterprise network include:

- LANs interconnected to provide access to computers or file servers in other locations

- End-user needs for higher bandwidth on the LANs

- Relaying technologies for WAN service


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A Big Picture of Enterprise Network(contd)

A campus is a building or group of buildings all connected into one enterprise network that consists of many local area networks (LANs).

A campus is generally a portion of a company/organization (or the whole company) constrained to a fixed geographic area.

Example of a campus network


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Four basic types of internetworking devices:

- Hubs

- Bridges

- Switches

- Routers

Most network designers are moving away from hubs and bridges and primarily using switches and routers

Selecting Internetworking Devices


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Internetworking Devices

Hubs (Concentrators)

- used to connect multiple users/network devices together, making them act as a single network segment

- act as repeaters by regenerating the signal as it passes through them

Bridges

- used to logically separate network segments within the same network

- operate at the OSI data link layer (Layer 2) and are independent of higher-layer protocols.


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Internetworking Devices(contd)

Switches - similar to bridges but usually have more ports- provide a unique network segment on each port, thereby separating collision

domains- Today, network designers are replacing hubs in their wiring closets with

switches to increase their network performance and bandwidth while protecting their existing wiring investments

Benefits of using switches:- High bandwidth- Improved performance (only selected frames are transferred between ports)- Low cost- Easy configuration (support self-configuration)- VLAN (IEEE 802.1Q)


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Switch: Learning Address

Station A sends a frame to Station C Switch caches station A MAC address to port E0 by learning the source address

of data frames The frame from station A to station C is flooded out to all ports except port E0

(unknown unicasts are flooded)

MAC address table

0260.8c01.1111

0260.8c01.2222

0260.8c01.3333

0260.8c01.4444

E0: 0260.8c01.1111

E0 E1

E2 E3DC

BA


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Switch: Learning Address (cont.)

Station D sends a frame to station C Switch caches station D MAC address to port E3 by learning the source Address of

data frames The frame from station D to station C is flooded out to all ports except port E3

(unknown unicasts are flooded)

MAC address table

0260.8c01.1111

0260.8c01.2222

0260.8c01.3333

0260.8c01.4444

E0: 0260.8c01.1111E3: 0260.8c01.4444

E0 E1

E2 E3 DC

A B


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Switch: Filtering Frames

Station A sends a frame to station C Destination is known, frame is not flooded

E0: 0260.8c01.1111E2: 0260.8c01.2222E1: 0260.8c01.3333E3: 0260.8c01.4444

0260.8c01.1111

0260.8c01.2222

0260.8c01.3333

0260.8c01.4444

E0 E1

E2 E3

XX DC

A B

MAC address table


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Switch: Broadcast and Multicast Frames

Station D sends a broadcast or multicast frame

Broadcast and multicast frames are flooded to all ports other than the originating port

0260.8c01.1111

0260.8c01.2222

0260.8c01.3333

0260.8c01.4444

E0 E1

E2 E3 DC

A B

E0: 0260.8c01.1111E2: 0260.8c01.2222E1: 0260.8c01.3333E3: 0260.8c01.4444

MAC address table


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Types of Switches

Switches can be categorized as follows:

LAN switches The switches within this category can be further divided into

Layer 2 switches and multilayer switches.

ATM switches ATM switching offer greater backbone bandwidth required by

high-throughput data services.

Workgroup ATM switches Campus ATM switches Enterprise ATM switches Multiservice access switches


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Topological Limitations of Switched Network A serious limitation of functional capabilities of switch is the impossibility of supporting loop

configurations of the network- Frame spawning- Endless frame circulation- Constant rebuilding of address tables- Allow the construction of only tree-like structures that guarantee the presence of exactly one route

between any two segments

MAC Addr Port

123 1

MAC Addr Port

123 2

MAC: 123

broadcastSegment 1

Segment 2


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Spanning Tree Compliant Switch

IEEE 802.1D spanning tree protocol

Using bridge protocol data units (BPDUs) to construct spanning tree

- Generated periodically (hello interval)

Normal traffic goes through root port and designated port

Eliminate looping in the network

In general tree topology built is not always optimal (why?)

root switch

designated switch


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Routers

Routers - separate broadcast domains and are used to connect different networks.- direct network traffic based on the destination network address (Layer 3)

rather than MAC address. - protocol dependent.

Benefits of using routers- Broadcast filtering- Hierarchical addressing- Communication between dissimilar LANs and interconnect disparate LAN and

WAN technologies- Optimal packet routing- Security- Policy routing- QoS routing- Multimedia group membership (multicast routing)


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Outline

Internetworking Devices LAN and WAN Design Enterprise Network Design Model Sever Placement


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Ethernet (IEEE 802.3)

IEEE 802.3 (Ethernet)- History

Proposed by Xerox, DEC, & Intel.- MAC

1-persistent CSMA/CD.- Cabling

An Ethernet LAN can consists of multiple segments connected by repeaters. A maximum of 4 repeaters can be used. In any case, the end-to-end maximum is 2500 meters.

Collision window period = 2tprop

tprop


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Ethernet (IEEE 802.3)

Cabling

10Base5 10Base2 10Base-T

Note: The transceiver is responsible for carrier detection and collision detection.


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Shared LAN

Inherent Contention Problem only one user access at a time create bottlenecks when network becomes busy access contention causes latency variation

Server 1 Server 2 Server 3

Hub 1 Hub 2 Hub 3

Single Segment

UsersA CB D FE G IH

Users Users


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Segmented LAN

Inherent Congestion Problem Bridge partitions collision domain and improves response time on same segment but, congestion at bridging ends

Server 1 Server 2 Server 3

Hub 1 Hub 2 Hub 3

Segment A

UsersA CB D FE G IH

Users Users

Segment BBridge1 0


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Switched LAN

Dedicated Switched Paths multiple and simultaneous switched paths at full rate remove collision domain but, shift bottlenecks to application domain

Server 1 Server 2Backbone

Hub 1 Hub 2 Hub 3

UsersA CB D FE G IH

Users Users

High-Speed LAN switch10Mb/s 10Mb/s

10Mb/s10Mb/s 10Mb/s

10Mb/sRouter

30Mb/s switch


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Switched 10/100 Mps

Asymmetrical Rates removed bottlenecks in application domain full high speed uplink possible

Server 1 Server 2Backbone

Hub 1 Hub 2

UsersA CB D FE G IH

Users Users

High-Speed LAN switch100Mb/s 100Mb/s

10Mb/s 10Mb/s

100Mb/sRouter

10Mb/s


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LAN Switching Operation

Destination address

Source address

Check sum

Data

Operates at the data link layer

Learns source addresses on the LAN

Transmits frame out the correct port based on the destination address

Floods frame to all ports when destination address is unknown

Filter frame when destination is on the same LAN segment

Is basically a bridge - but can switch more than one frame at a time

Basic MAC Frame


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Shared LAN Designs

- Network A has 500 users on 5 separate 100-node shared Ethernet segment- Each user has roughly 100 kbps- Network can handle audio conferencing

Router

Hub HubHubHubHub

10 Mbps

100 users per segment100 kbps per user

Network A

100 users shared 10 Mbps uplink


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Shared Ethernet and Switched Ethernet LAN Designs

10 users are connected to a shared Ethernet hub Each hub is connected to a dedicated 10 Mbps Ethernet switch port

Each hub gets 10 Mbps giving each users roughly 1 Mbps

can run medium quality video applications

Network B uses

both hubs and switches

10 Mbps

50 Mbps

1 Mbps

50 Mbps switched uplink

10 users shared 10 Mbps uplink


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Switched LAN Designs Network C eliminates the shared Ethernet hubs Each user has a dedicated 10 Mbps connection to the LAN via a direct connection to

the switch port Can support high quality multimedia applications

Router

1 users per segment10 Mbps per user

Network C

Switch

10 Mbps

50 Mbps

Full-rate switched connection


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To increase bandwidth for running multimedia applications, one could consider using the following high-speed backbone technologies:

Fast Ethernet (100 Mbps) Gigabit Ethernet ATM FDDI (getting less popular)

High-Speed LAN Design


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Deliver 100 Mbps over cat 5 UTP or fiber cable

Two main advantages:

- Relatively inexpensive (assuming cat 5 UTP is present)- Simple to migrate from traditional 10Mbps Ethernet

Support a variety of network design scenarios:

- High-speed client-server connectivity

- High-speed interswitch communication- High-speed backbone

Fast Ethernet


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High-speed client-server connectivity- Servers on Fast Ethernet can transmit data to clients that are connected via Fast

Ethernet or switched 10 Mbps Ethernet

- Fast Ethernet also provides a straightforward migration path for client stations to 100 Mbps

Fast Ethernet(contd)

(e.g. Cisco 4x00/7x00series router)

10-Mbpsswitched Ethernet

Client access

e.g. Catalyst 5000

100 Mbps100 Mbps

File/printsever

Videosever

LAN switch

100 Mbps

Asymmetrical-rate connection


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High-speed interswitch communication Useful in a microsegmented environment in which each client has a dedicated

10 Mbps segment With Fast Ethernet connection between switches, a client can communicate

with another client attached to a different switch without sacrificing bandwidth

100 Mbps

100 Mbps100 Mbps

Switch


10 Mbps Switched Ethernet

Client access

10 Mbps Switched Ethernet

Client access

High-speed switched uplinks


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High-speed backbone Fast Ethernet connections over CAT5 UTP are limited to 100 meters The distance can be extended to 2 km by using fiber Can use Fast Ethernet over fiber as a backbone to interconnect switches and routers

within a campus However, in practice, Fast Ethernet is rarely used as backbone technology

- Gigabit Ethernet and ATM are better choices as backbone technologies


100 Mbps

e.g. Catalyst 5000

e.g. Catalyst 5000

e.g. Catalyst 5000

e.g. Catalyst 5000

100 Mbps100 Mbps

Building 1

Building 4

Building 3

Building 2

LAN switch

High-speed backbone switched connections


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Virtual LAN (VLAN)

VLAN allows for grouping of network devices (ports, stations, switches, etc) into virtual (logical) broadcast groups

is independent of physical location (except using port addressing) specified by switch port number, MAC address, and protocol

VLAN achieve the following benefits: isolate different broadcast domains restrict routing of packets (especially broadcast packets) restrict access for some servers or services

1

8R Switch

VLAN-1

(subnet 1)

VLAN-2

(subnet 2)

E

Fast Ethernet

Member of both VLANsE

7

34

6


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VLAN Addressing

Static VLANs- Assign ports (port-centric)- All nodes attached to same switch port must be in same VLAN- Benefits: secure, easy to configure and monitor

Dynamic VLANs- Assigned using centralized VLAN management application - Assigned based on MAC address, logical address, or protocol type- Notification when unrecognized user is added to network- Benefits: less wiring reconfiguration

VLAN5

Static VLAN

MAC = 1111.1111.1111

TrunkDynamic

VLAN

VMPS1111.1111.1111 = vlan 10

VLAN10

Port e0/9Port e0/4

L2 Header VLAN Tag DataCheck sum


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VLAN Segmentation

Medium bandwidth users

Repeater

100Mbps Switch

Very high bandwidth users

Low bandwidth users

10/100Mbps Switch

1010

VLAN 2VLAN 1

Server

Server

Router

Switches and routers each play an important role in VLAN design. Switches are the core device that controls individual VLANs while routers provide interVLAN communication

Subnet 1 Subnet 2


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VLAN Routing Host A wants to communicate with host D, so it sends address resolution protocol (ARP)

frame with host Ds destination IP and broadcast MAC addresses Switch broadcasts request to all other ports in VLAN 10, including to the router Router recognizes it can reach host Ds network, replies ARP response frame with its own

MAC address as the destination MAC address to reach host Ds network Host A sends all subsequent traffic with host Ds IP and the routers MAC address Router recognizes destination network is on VLAN 20, hence routes all frames to the switch

with a VLANID 20 The switch, in turn, deliver the frame to host D


Subnet 1 Subnet 2


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VLAN example

Simplification of network management by facilitating network reconfigurations (moves and changes)


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Evolve Shared-Media Networks to Switching Internetworks

example of how a LAN switch can be used to segment a network:

network designers retain their hubs and routers, but insert a LAN switch to enhance performance.

Phase 1: Using Switches For Micro-segmentation

Micro-segmentation

Routed segments


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Evolve Shared-Media Networks To Switching Internetworks (contd)

Phase 2: Addition of high-speed backbone technology and routing between switches

Backbone routers are attached to either Fast Ethernet or ATM switches.

Switched backbone

Switched segments

Distribution router


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Evolve Shared-Media Networks To Switching Internetworks(contd)

Phase 3: Distributing routers between high-speed core and LAN switches.

routers are distributed between the LAN switches in the wiring closet and the high-speed core switch. The network backbone is now strictly a high-speed transport mechanism with all other devices, such as the distributed routers, at the periphery Distribution

routers

High-speed core


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Evolve Shared-Media Networks To Switching Internetworks(contd)

Phase 4: End-to-end switching with VLAN and multilayer switching capability.

It involves end-to-end switching with integral VLANs and multilayer switching capability. By this point, Layer 2 and Layer 3 integrated switching is distributed across the network and is connected to the high-speed core.

VLAN segments

IP Switch Controller

SwitchUpstream

nodeDownstream

node

IP Switching


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Trends in Campus Design

switched segments

Distribution high-speed switches Distribution routers


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Traditional Campus-VLAN Design

Core serversVLAN routing


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Campus-Wide VLANs and Multilayer Switching

VLAN switching


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Summary of LAN Technologies

LAN Technology Typical Uses

Routing technologies Routing is a key technology for connecting LANs in a campus network. It can be either Layer 3 switching or more traditional routing with Layer 3 switching and additional router features.

Gigabit Ethernet Gigabit Ethernet builds on top of the Ethernet protocol, but increases speed ten-fold over Fast Ethernet to 1000 Mbps, or 1 Gbps. Gigabit Ethernet provides high bandwidth capacity for backbone designs while providing backward compatibility for installed media.

LAN switching technologies Ethernet switching

Ethernet switching provides Layer 2 switching, and offers dedicated Ethernet segments for each connection. This is the base fabric of the network.

ATM switching technologies

ATM switching offers high-speed switching technology for voice, video, and data. Its operation is similar to LAN switching technologies for data operations. ATM, however, offers high bandwidth capacity.


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WAN Technologies

Asymmetric Digital Subscriber Line- Converts existing twisted-pair telephone lines into access paths for multimedia and high-speed data

communications.

Integrated Services Digital Network (ISDN)- used for cost-effective remote access to corporate networks.

- provides support for digital voice, video and data transport services on public telephone networks.

Switched Multimegabit Data Service (SMDS)- provides high-speed, high-performance (bursty) connections across public data networks

- also deployed in metropolitan-area networks (MANs).

X.25- provide a reliable WAN circuit or backbone.

- provides support for legacy applications.

Frame Relay- public network WAN technology based on packet switching (lite version of X.25 error-control)

WAN ATM- can be used to accelerate bandwidth requirements.

- support for multiple QoS classes for differing application requirements for delay and loss.


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WAN Devices

Routers offer many services, including networking and WAN interface ports

WAN switches connect to WAN bandwidth for voice, data, and video communication multiport networking device typically switches such traffic as Frame Relay, X.25, and Switched

Multimegabit Data Service (SMDS) operate at the data link layer, filter, forward, and flood frames based on

the destination address of each frame

Communication servers concentrate dial-in and dial-out user communication


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WAN Devices(contd)

Modems: interface voice-grade services. Modems include CSUs/ DSUs and TA/NT1 devices that interface ISDN services. Modulating and demodulating the signal, enabling data to be transmitted over voice-grade telephone lines (analog)

Modem Modem

WAN

CSU/DSUrouter

WANswitch

Digital-interface device: channel service unit (CSU)/data service unit (DSU) is placed between the switch and the router. Sometimes, CSU/DSUs are integrated in the router box.

Analog-interface

Digital-interface

Typically for remote WAN access

Typically for WAN inter-connection


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WAN Devices(contd)

WAN

ISDN TA

Switch

ISDN TA : a device used to connect ISDN Basic Rate Interface (BRI) connections to other interfaces. A TA is essentially an ISDN modem

ISDN Terminal Adapters

Digital-interface


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WAN Physical Layer

Modem

EIA/TIA-232 V.35 X.21 HSSI others

CSU/DSU Modem DCE Endpoint of the WAN provider's side of the communication facility

DTEEndpoint of the user's device

on the WAN ink

EIA/TIA-232 -A common physical-layer interface standard, supports unbalanced circuits at signal speeds of up to 64 kbps. formerly known as RS-232

V.24-An ITU-T standard for a physical-layer interface between DTE and DCE X.21-An ITU-T standard for serial communications over synchronous digital lines. The X.21protocol is used primarily in Europe and Japan.

Physical-interface

Serial linkDTE DCESerial DCE & DTE

Clock rates range form 300 bps to 8 Mbps


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The WAN Data Link Layer

X.25. Frame Relay

Dedicatedpoint-to-point

Cisco HDLC, PPP

Packetswitched

Circuit switched

router

ISDN D channelISDN B channel


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Use of Frame Relay and ISDN WAN Links

Core WAN

Campusbackbone

Site 1 Site 2 Site 3

24

6

Site 4

LAN switch

Site 4

Site 5Site 6

Frame Relay

ISDN

Serial link

Remote siteRemote site


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WAN bandwidth is a scarce resource and increasing WAN bandwidth is not easy as it is expensive

If additional WAN bandwidth is needed, first look at available circuit-switched technologies: Switched-56, switched-T1, and ISDN

- Charges on these services are based on connection time

- These services can also be configured as backup service if they are used together with other WAN services such as leased lines

WAN Design Considerations


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Remote Connection Design

Remote connections link single users (mobile users and/or telecommuters) and branch offices to a local campus or the Internet

Typically, a remote site is a small site that has few users and therefore needs a low bandwidth WAN connection

Network designers typically choose between dial-up and dedicated WAN options for remote connections. Remote connections generally run at speeds of 128 Kbps or lower.


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Policy-based routing can be used for networks in which both circuit-switched WAN and leased line connections are used

- Traffic can be routed over different WAN links based on traffic type- E.g. Route e-mail and FTP traffic over a 56 kbps leased line and a video

conferencing session over ISDN

ISDN

56kbps leased lineFTP

E-mail

Proshare Client FTP client FTP host Proshare client

Policy-based routing

Video over circuit-switched WAN


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Outline


LAN and WAN Design


Sever Placement


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Enterprise Network Design Model--- Structure, Hierarchy and Modularity

Structure ---- creates failure domain boundaries

Hierarchy --- is functional and divides the problem

Modularity --- Create manageable building blocks

Fundamentally, we break the network design into manageable blocks so that the network will function within the performance and scale limits of applications, protocols and network services


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Modularity Building Block vs. Product Focus

- A module is a functional building block, not a product mapping

- A module is defined by the functions it performs, not what boxes are used

Building-Block Approach : Designing and building network modules that are then assembled to create a large hierarchical network provides several benefits:

- Ease of growth

- Streamlined training

- Distributed management

- Fault isolation and troubleshooting


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Modularity Example


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Generic Modular Campus Design


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Hierarchical Design Model

Building backbone

WAN

Campus backbone

Remote Site 1 Remote Site 2

Core Layer(Network Backbone)

Distribution Layer

Access Layer

Remote workgroups Local workgroups

Broadcast domains

Bro

adca

st

dom

ain

Bro

adca

st

dom

ain

LAN switch

LAN switch

LAN switch LAN switch

router

Hierarchy: each layer provides a unique function


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Hierarchical design model

- Design the network in layers to simplify the design task

- Each layer is focused on specific functions, thereby allowing the networking designer to choose the right systems and features for the layer

Advantages

- Hierarchical design facilitate changes.

- Modularity in network design allows replication of design elements as the network grows.

- The cost and complexity of making the upgrade are constrained to a small subset of the overall network.

- Facilitate the identification of failure-points in a network by structuring the network into small, easy-to-understand elements.

- Network managers can easily understand the transition points in the network, which helps identify failure points.

Hierarchical Design Model


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The hierarchical design model includes three layers:

Core layer: provides optimal transport between core routers and distribution sites

Distribution layer:

- Provides network services to multiple LANs within an enterprise network, e.g. campus backbone

- provides policy-based connectivity, e.g. broadcast/multicast domain, VLAN routing, etc.

Access layer: provides workgroup and user access to the network, e.g. Ethernet LAN

Hierarchical Design Model (contd)


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Hierarchical Design Model(contd)

Building backbone

WAN

Campus backbone

Remote Site 1 Remote Site 2

Core Layer(Network Backbone)

Distribution Layer

Access Layer

Remote workgroups Local workgroups

Broadcast domains

Bro

adca

st

dom

ain

Bro

adca

st

dom

ain

LAN switch

LAN switch


router

Distribution Integration

Concentration


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Provides fast connections between remote sites: Optimized paths between interconnections

Should not perform any packet manipulation, such as access control and packet filtering, that would slow down the network

Usually implemented as WAN, the services typically are leased from a telecom service provider: Efficient and controlled use of bandwidth

The WAN in general requires redundant paths to keep the network continues functioning even in case of link failure

Main design issues of WAN:

- Load sharing, rapid convergence of routing protocols, and efficient use of bandwidth

Core-Layer Site DSite A

Site B

Site C


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Core Routing Illustrated (contd)

Ensure traffic engineering policies and latency are consistent

Fast-Converging Designs enables- alternative path routing (load sharing) - consistent steady-state performance- consistent failure mode behavior

Preventing the possibilities of partitioning the core

Example Enterprise Core Design


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Core Routing: Fast Converging Design

Create Fast Converging designs- use topology or parallel paths between nodes to create load sharing for

consistent, steady-state performance and fast re-route - In the example, A to B has three equal-cost next hops

Three equal hop-count paths from A to B for load balancing and fast re-route


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Core Routing: Consistent Routing Performance

Define diameter(s) between Core routers- Design for a specific number of maximum hops for consistent traffic engineering and

latency - The example has a maximum of four hops through the core. Single-node or double-

link failure does not increase maximum hops

Maximum network diameter of 4 hop-count from A to B for consistent routing performance


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Core Routing: Consistent Failure Mode Behavior

Use equal bandwidth links- Enable alternative-path routing, consistent steady-state performance, and

consistent failure mode behavior

- In the example one link fails, A has three next hops and they remain equal routing metric cost to get to B)

Change in topology in the core without disruption of distribution layer routing


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Core Routing: Prevent Partitioning

Prevent partitions- In the example, it takes four simultaneous link failures to partition this

design (or three link failures to isolate a single core router)

Prevent network partitioning or node isolation due to link failures


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Core Layer Topology

The 8-node Cube topology illustrates the core layer attributes in the prior slides but the principles of core layer design remain the same with other topologies

Hyper-Cube:

Number of nodes (N) : 8

Core interfaces: 24

Number of circuits: 12

Compared to full mesh

Number of nodes: 8

Core interfaces: 56

Number of circuits: 28


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Core: Full Mesh (Example)

Peer / adjacency intensive: - Central core (full mesh) routers have N-1 adjacencies, which makes scaling difficult

Difficult to upgrade: - As a core router is added, full connectivity requires changes to every router

Expensive: - Huge number of interfaces and circuits on the core routers


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Core: Metro Ethernet Ring (Example)

Use point-to-point Gigabit Ethernet for improved network performance

Number of nodes: 8Core interfaces: 16Links: 8

This Structure still has some undesirable attributes (two link failures result in a partitioned core)


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Core: Metro Ethernet Cube Example To limit negative failure mode behavior of ring add four more circuits to create a cube

Number of nodes: 8

Core interfaces: 24

Links: 12

Subnet per point-to-point link

This structure controls the failure domains by increased number of links


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A boundary between the core and the access layers

the backbone network which interconnect LANs usually based on Gigabit Ethernet or ATM

packet manipulation and filtering can take place

Routers with high densities of network aggregation ports will be a part of the Distribution layer

Distribution layer

Site A

Campus backbone

Building backbone

WAN


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Provides policy-based connectivity, i.e. routers are programmed to allow only those traffic that the network manager has determined acceptable on the backbone network

Policy:

- Set of rules that governs end-to-end distribution of traffic through a backbone network

- E.g. An organization might want to regulate backbone traffic to a maximum of 10 percent average bandwidth during the work day and 1-min. peaks of 30 percent utilization

- E.g. To limit the traffic on the backbone, one might want to filter off the Service Advertisement Protocol messages sent by NetWare services, i.e. all NetWare services should be provided locally and should not be advertised remotely

Distribution layer(contd)


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Distribution layer can include functions - Address or area aggregation- Departmental or workgroup access- Broadcast/multicast domain- VLAN routing- Security

Good network design practice would not put end stations (such as servers) on the backbone

- The backbone acts strictly as a transit path for traffic between workgroups in different buildings, or from workgroups to campus-wide servers

- Distribution layer can also be a redistribution point between routing domains

- It can also be a point at which remote sites access the corporate network

Distribution layer(contd)


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Distribution Hub-and-Spoke Example

Network scale:

Insulate rest of the network from local or group-level complexity

Aggregation:

High densities of adjacencies (routing peers)

High densities of interfaces

Security:

Access list processing

Firewalls

Process intensive & appliance services:

QoS services

Rate limiting

Content services


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Distribution: Frame Relay Example


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Distribution: Metro Ethernet Example


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Distribution: Metro Ethernet Example (contd)


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Small and Medium Business

Emulated LAN model

For a Small number of sites, a flat network may be viewed as an acceptable risk.

- Single bridge domain ( 1 VLAN)- Single subnet- Single SLA- Single protection attributes- Single availability attributes

Single failure domain


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Building backbone

LAN switch

LAN switch


WAN links

terminal

Access layer

remote workgroups local workgroups


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The point at which end users are connected to the network

It may also use access lists or filters to further optimize the needs of a particular set of users

Main functions:- Provide logical segmentation

- Isolate broadcast traffic from the workgroup

- Provides access to the enterprise for a group that has common, locally significant characteristics:

Policy Security QoS marking Addressing scheme QoS admission Service

Access layer Overview


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Access Layer Design Examples

Common Concepts (workgroup):- Community of Interest- Same subnet (or small set of subnets)- Same default gateway (or set of

gateways)- Common local architecture- Common security constraints- Common QoS Marking and admission

policies- Locally significant services- DHCP servers


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Not necessary to have the three layers exist in clear and distinct physical entities

The layers are used to represent the functionality that must exist in a network and are used to aid the network design

The instantiation of each layer can be in distinct routers or switches, or combined in a single device, or can be omitted altogether

Alternatives to the three-layer design are one-layer and two-layer designs

Alternatives for Hierarchical WAN Design


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One-layer design

CoreWAN

Remote Site A Remote Site B

Light traffic load

Heavy traffic load

Bro

adca

st

dom

ain

Bro

adca

st

dom

ain

Bro

adca

st

dom

ain

Remote Site C

LAN switch

LAN switch

LAN switch


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One-layer design (contd)

One-layer design is sufficient in designing small networks.

Typically used if there are only a few remote locations in the company, and access to applications is mainly done via the local LAN (to servers)

Each site is its own broadcast domain.

Key design issue: Where should the servers be placed?

- Distributed across multiple LANs

- Concentrated in a central server farm location


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Two-layer design

WAN

Site A Site B Site C

Site D Site E

Site FWAN link

WAN link

WAN link

A WAN link is used to interconnect separate sites.

Inside each site, multiple LANs may be implemented, with each LAN segment being its own broadcast domain.

Site F is a concentration point from WAN links

Subnet 1Subnet 2

Subnet 3 Subnet 4


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Structure: Typical Large Campus


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Structure: Typical Large WAN

Distribution of MANs


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Examples of Enterprise Modules Aggregation of WAN

Concentration of Firewalls and gateways


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Networks with Multiple Levels of Structure

Dual core layers


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Structure: Controlling Failure

Well-defined failure domains are created by both routing and switching

Failure isolation and troubleshooting are improved by applying a modular structure with hierarchy


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Outline


LAN and WAN Design


Sever Placement


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Server placement

Why consider:

- Servers is related to who will be accessing them

- The placement of servers affects traffic patterns in the WAN

Placement principles:

- If a server is to be accessed by users from different sites, placing it at a higher layer in the hierarchy will result in a better bandwidth usage

- On the other hand, placing the server at the access layer of the site where the largest concentration of users is located will limit the amount of traffic crossing the WAN link


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Server placement(contd)

WAN

Campusbackbone

othersite

othersite

Site 1 Site 2 Site 4Site 3

1

2

3

4

5 6

Core Layer

Distribution Layer

Access Layer

7

LANswitch

workgroupsever

Placement of server based on user needs


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Heavy load on remote links

Server placement

WAN

Campusbackbone

othersite

othersite


1

2

3

4

5 6

Core Layer

Distribution Layer

Access Layer

7

LANswitch

Enterprisesever

remote workgroups


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Server placement(contd)

WAN

Campusbackbone

othersite

othersite


1

2

3

4

5 6

Core Layer

Distribution Layer

Access Layer

7

LANswitch

Enterprisesever

Moving the server to correct location to free up bandwidth


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Page 100

THANK YOU

THE END

Unit 3 Enterprise Network Technology DesignOutlineA Big Picture of Enterprise NetworkA Big Picture of Enterprise Network(contd)A Big Picture of Enterprise Network(contd)Slide Number 6Internetworking DevicesInternetworking Devices(contd)Switch: Learning AddressSwitch: Learning Address (cont.)Switch: Filtering FramesSlide Number 12Types of SwitchesTopological Limitations of Switched NetworkSpanning Tree Compliant SwitchRoutersOutlineEthernet (IEEE 802.3)Ethernet (IEEE 802.3)Shared LANSegmented LANSwitched LANSwitched 10/100 MpsLAN Switching OperationSlide Number 25Slide Number 26Slide Number 27Slide Number 28Slide Number 29Slide Number 30Slide Number 31Slide Number 32Virtual LAN (VLAN)VLAN AddressingVLAN SegmentationVLAN RoutingVLAN exampleEvolve Shared-Media Networks to Switching InternetworksEvolve Shared-Media Networks To Switching Internetworks (contd)Evolve Shared-Media Networks To Switching Internetworks(contd)Evolve Shared-Media Networks To Switching Internetworks(contd)Trends in Campus DesignTraditional Campus-VLAN DesignCampus-Wide VLANs and Multilayer SwitchingSummary of LAN TechnologiesWAN TechnologiesWAN DevicesWAN Devices(contd)WAN Devices(contd)WAN Physical Layer The WAN Data Link LayerUse of Frame Relay and ISDN WAN LinksSlide Number 53Remote Connection DesignSlide Number 55Slide Number 56Enterprise Network Design Model --- Structure, Hierarchy and ModularityModularityModularity ExampleGeneric Modular Campus DesignSlide Number 61Slide Number 62Slide Number 63Slide Number 64Slide Number 65Core Routing Illustrated (contd)Core Routing: Fast Converging DesignCore Routing: Consistent Routing PerformanceCore Routing: Consistent Failure Mode Behavior Core Routing: Prevent PartitioningCore Layer TopologyCore: Full Mesh (Example)Core: Metro Ethernet Ring (Example)Core: Metro Ethernet Cube ExampleSlide Number 75Slide Number 76Slide Number 77Distribution Hub-and-Spoke ExampleDistribution: Frame Relay ExampleDistribution: Metro Ethernet ExampleDistribution: Metro Ethernet Example (contd)Small and Medium BusinessSlide Number 83Slide Number 84Access Layer Design ExamplesSlide Number 86Slide Number 87Slide Number 88Slide Number 89Structure: Typical Large CampusStructure: Typical Large WANExamples of Enterprise ModulesNetworks with Multiple Levels of StructureStructure: Controlling FailureSlide Number 95Slide Number 96Slide Number 97Slide Number 98Slide Number 99Slide Number 100

network enterprise

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