Network design

Topic 2Existing network infrastructure

Agenda

• Network maps• Network health• Network availability• Network utilisation• Network efficiency

Starting point

• Understand the existing network structure • Document the topology and physical structure• Understand what the network is used for and

how it behaves– Performance– Bottlenecks

• Design for interoperability with the existing network and capacity for future

Characterise the network infrastructure

• Locate major internetwork devices• Locate network segments• Develop network maps• Document naming and addressing• Document types and lengths of cables• Investigate building and environment

constraints

Develop network maps• High level map– Showing states, cities and campuses– WAN connections– WAN and LAN connections between buildings and between

campuses• Campus maps– Buildings and floors, rooms and cubicles– Location of major servers – Location of routers and switches– Location of mainframes– Location of network management stations– Location of VLANs– Indication of workstations (not each one)

Logical maps, applications and services

• Locate applications and services used by network users– Custom applications– Internal web services, intranet– Web caching servers– Email– FTP– Print and file sharing– Application servers– Database servers and data stores

• Tools such as CartoReso– http://cartoreso.campus.ecp.fr/index.php

Logical mapsnetwork services

• Security servers – TACACS and Radius• DHCP• DNS• NAT• Print Servers• SNMP• VPN devices • RAS servers

Logical mapsLayer 3 topology

• Locate routers, links and interface names• Locate networks and subnets– Route summarisation– Route aggregation

• Routing protocol information– Hot standby router protocol groupings– OSPF areas– Redistribution points– Router roles such as DR for OSPF

Logical mapsLayer 2 topology

• Layer 2 devices– Switches and access points

• WAN and LAN technologies– Frame, ISDN, Ethernet

• Service provider for WAN links and circuit IDs• STP information – Root bridge location, root ports, redundant links

• VLANs• Trunks between switches

Modular design

Topology for:

• Core • Distribution• Access

Wiring and mediaWiring charts

• Types of cables• Cables distances• Labelling on equipment and cables• Connections between buildings including number

of wires and type of media and distance• Location of telecommunications room and wiring

closets• Vertical wiring runs• Horizontal wiring runs

Building and environmental constraints

• Within buildings:– Air conditioning– Heating– Ventilation– Power– Protection from EMI– Security locks– Space for cable conduits, patch panels, equipment racks

and work areas• Between buildings:– Flooding, heavy traffic to jostle cables, legal right of way,

line of sight for wireless

Health of existing network

• Baseline measurements on the performance of the existing network– Select an appropriate timeframe• Multiple time frames and sufficient time frames• Don’t measure for typical performance when the

network is under abnormal load

– Select a typical time period of normal performance

– Measure for errors, packet loss and latency

Network availability

• Gather statistics– MTBF mean time between failure – MTTR mean time to repair for each major

segment – Find out the causes of recent and disruptive

periods of downtime

Network utilisation

• How much bandwidth is in use during a specific interval?

• Measure bandwidth utilisation by protocol– Consider broadcast traffic and unicast traffic– Relative network utilisation usage by

protocol/total usage– Absolute network utilisation

• Use a protocol analyser to measure traffic

Measure network accuracy

• Measure the bit error rate– Use a BER tester – Show interface commands to find the number of

errors on serial interfaces

• Look for CRC errors on frames on Ethernet networks– Show interface switchport

• Measure lost packets and response times

Network efficiency

• Maximum frame sizes ensure large amounts of data per frame and therefore the number of frames and round trip delays are reduced

• Large window size means multiple frames are accepted before pausing to acknowledging

• Increase window sizes on servers and clients• Increase MTU on router interfaces– necessary for tunnel traffic – extra headers may exceed MTU and fragment

Delay and response time

• Send ping packets and measure RTT round trip time

• Measure variance for realtime applications which do not tolerate jitter

• Measure response times for typical applications and functions:– Checking email– Sending a file– Loading a web page– Printing

Status of major routers, switches and firewalls

• CPU utilisation - How busy the device is• How many packets have been processed• How many packets have been dropped• Status of buffers and queues– Show buffers– Show environment– Show interfaces– Show memory– Show processes

• SNMP can also monitor the health of devices

Tools• Protocol analysers– EtherPeek from WildPackets– Wireshark®

• Network monitoring tools:– MRGT multi router traffic grapher

• Network traffic load and performance characteristics– Cricket – Periscope Network Analysis– Netflow

Agenda

• Network maps• Network health• Network availability• Network utilisation• Network efficiency