Specifications

TWCB Overview
April 16, 2009 Page 3 of 14
Figure 1 TWCB Configuration Overview
TheN‐Seriesrouterdoesnotactasacacheforwebobjects;rather,itredirectsHTTPrequeststo
localserversonwhichwebobjectsarecached.Thecache‐serversshouldhaveaweb‐basedproxy
cacherunning.TheSquidapplicationisanexampleofaweb‐basedproxycache.
Inourexample,auseronthe10.10.10.0/24subnetmakesawebrequestfromthewebsitehost.The
response,containingtheweb‐object,issenttoboththerequestinguserandacacheforthat
end‐userthatresidesonacacheserver.
Therouterselectsacacheserverto
cachethewebobjectsforeachend‐user.Oncecreated,allweb
objectsforthatend‐userwillbesenttothatcacheunlesstheend‐userisamemberofapredictor
round‐robinlistassociatedwithaserverfarm.Webobjectsthatbelongtomembersofapredictor
round
‐robinlistareloadbalancedacrossallthecache‐serversconfiguredforthatserverfarm.
End‐userswithparticularlyheavywebusageshouldbelongtoapredictorround‐robinlistto
avoidoverwhelmingtheresourcesofasinglecacheserver.
Onceawebobjectresidesinthecache,anyfuture
requestsforthatwebobjectwillbehandledby
thecacheserveruntilthecacheentryexpires.Cacheentryexpirationisconfiguredinthe
web‐basedproxycacheapplicationinstalledonthecacheserver.
TherearefivecomponentsinaTWCBconfiguration:
•Theserverfarm
•Thecacheserver
•Theweb‐cache
•Theoutbound
interface
•Theswitchandrouter
Global
Internet
Users
Initial Web Object Request
Initial Web Object Response
All Subsequent Requests for
the same object
Router
Web Site Host
Cache1
186.89.10.51
186.89.10.55
Subnet 10.10.10.0/24
176.89.10.20
176.89.10.32
176.89.10.45
176.89.10.50
176.89.10.52
Cache Servers
Server Farms
s1Server
s2Server