WAN design ผศ. ดร. อนันต์ ผลเพิ่ม Asst.Prof.Anan Phonphoem, Ph.D. Computer Engineering Department Kasetsart University, Bangkok, Thailand

2 of 26 Types of WAN Service

3 of 26 WAN Technology TechnologyTypical Uses Leased LinePPP networks, hub and spoke, back-ups ISDNRemote-access, voice, video, back-ups Frame RelayFast, efficient mesh between remote sites

4 of 26 WAN requirements Optimise WAN bandwidth Minimise cost Maximise the effective service to end users

5 of 26 LAN/WAN integration LAN/WAN, previously logically separated, must now be fully integrated for seamless performance Both now must be able to handle... Voice traffic (VoIP) Bandwidth intensive multimedia applications Video conferencing On-line training Increased business critical data access

6 of 26 Goals Availability Total cost of ownership

7 of 26 Concerns Environmental variables Performance constraints Networking variables

8 of 26 WAN Design strategies Mesh Network is flat All routers perform same function Expansion proceeds haphazardly  Hierarchical  Organized in layers  Easier to implement/Troubleshooting  Scalability  Predictability

9 of 26 Important of Layers Designing networks using the OSI model designed in layers simplify the tasks required for internetworking Design elements can be replicated as grows Therefore, networks should be designed using a hierarchical model. Unfortunately, most networks are thrown together into a mesh ( “ a mess! ” ) with little or no vision of future needs.

10 of 26 Benefit of Hierarchical Design Scalability allows for future growth without sacrificing control or functionality Ease of Implementation logically constructed layers specify the functions of each layer Ease of troubleshooting well-defined functions at each layer aid in the isolation of problems

11 of 26 Benefit of Hierarchical Design Predictability behavior of functional layers can be estimated and planned for Protocol support allows easier implementation of future technologies because the network has been logically constructed Manageability All the above aids net. admin. in overall management of the network

12 of 26 The Hierarchical Design Model The Three-Layer

13 of 26 The Hierarchical Design Model The Three-Layer Core layer--provides transport between remote sites Distribution layer--provides policy-based connectivity Access layer--provides workgroup/user access to network

14 of 26 Core Layer Fast WAN connections between remote sites Core links are normally point-to-point with no host devices Core services include: T1/T3 Frame Relay ATM SMDS

15 of 26 Distribution Layer Provides WAN services to multiple LANs Usually the campus backbone Uses Fast Ethernet (or Gigabit Ethernet) Used on large sites to interconnect blgs.

16 of 26 Access Layer Usually a LAN or group of LANs Gives access to specific users and workgroups This layer is where all hosts (including servers) are attached to the network

17 of 26 WAN Layer Functions Core Layer Functions Distribution Layer Functions Access Layer Functions

18 of 26 Core Layer Functions Optimize Transport Between Remote Sites Redundant paths to guard against circuit outages Provide load sharing and rapid convergence when link states change Efficient use of bandwidth by... Implementing scalable routing protocols and Blocking local traffic access to the core

19 of 26 Distribution Layer Functions Policy-Based Connectivity Boundary definition & packet manipulation Control access to services of the core layer and other distribution layer routers VLAN routing Address aggregation (i.e., subnets) & route optimization ACLs and other security measures

20 of 26 Access Layer Functions Workgroup & User Access to the Network Isolation of Broadcast Traffic Shared and Switched Bandwidth MAC-layer filtering Microsegmentation

21 of 26 Other Hierarchical Options One-Layer Design Two-Layer Design

22 of 26 One-Layer Design Only a few remote sites need to be connected Servers are placed in farms or in each workgroup to reduce traffic on the backbone

23 of 26 Two-Layer Design WAN link is used to interconnect separate sites Link does not have to be dedicated. An alternative would be ISDN.

24 of 26 Hierarchical Design Advantages Controlling data traffic patterns through source/destination network layer addressing A packet only needs to travel up the hierarchy as far as it needs to find the destination. With good design, most traffic would be contained in the access layer with users accessing their workgroup servers

25 of 26 Hierarchical Design Advantages Server Placement Enterprise Servers needed by all workgroups should be placed in the Distribution Layer (e.g. , DNS, etc.) Workgroup Servers needed by a unique set of users should be placed in the Access Layer, preferably in the same broadcast domain as the users

26 of 26 References Cisco course material Allan Johnson’s material (from cisco) user:dam0c00k’s material (from cisco)