Specifications

TWCB Overview
April 16, 2009 Page 5 of 14
Thepredictorround‐robinfeatureallowsforthecreationofupto10userlists.Membersofa
predictorround‐robinlistnolongerhaveasinglecacheonasinglecacheserver.Instead,web
objectsforlistmembersarecachedacrossallcacheserversassociatedwiththisserverfarmin
a
roundrobinfashion.Aserverfarmwithaconfiguredpredictorround‐robinwillonlycache
membersofpredictorround‐robinlistsassociatedwiththatserverfarm.Youmusthaveatleast
twoserverfarmsifyouhavebothuserswhobelongtoapredictorround‐robinlistandusers
who
usethedefaultcachingbehavior.
The Cache Server
Thecacheserveristhephysicalserveronwhichanend‐usercacheresides.Eachcacheserver
belongstoaserverfarm.Youcanconfigureupto128cacheserversperweb‐cache.Youcreatea
cacheserverbyenteringitsIPaddresswithintheweb‐cacheserverfarmconfigurationcommand

mode.Onceentered,youareplacedinTWCBcacheserverconfigurationcommandmode.
WithinTWCBcacheserverconfigurationcommandmode,youcanselectthetypeoffaildetection
thatwillbeusedbythiscacheserverandsetitsparameters.Faildetectionspecifiesthemethod
thatwillbeusedby
theroutertodeterminewhetherthecacheserverisinanupordownstate.
Faildetectiontypecanbesettoping,application,orboth.Theapplicationmethoddefaultstoa
checkofserviceavailabilityonport80.Anon‐standardHTTPportcanbeconfigured.The
applicationmethodwill
usethisconfigurationwhencheckingserviceavailability.Boththe
intervalbetweenretriesandthe numberofretriesforeachmethodareconfigurable.
Youcanconfigurethemaximumnumberofconnections(bindings)allowedforthiscacheserver.
Maximumconnectionsdefaultto5000.
Onceacacheserverisconfigured,youmustplace
itinserviceforthecacheservertobeactiveon
theserverfarm.
The Web-Cache
Theweb‐cacheisalogicalentityinwhichallserverfarmsreside.ThecurrentTWCB
implementationsupportsasingleweb‐cache.Youcreateaweb‐cachebynamingitinrouter
configurationcommandmode.Onceentered,youareplacedinTWCBweb‐cacheconfiguration
commandmode.OnceinTWCBweb
‐cacheconfigurationcommandmode,youcan:
•Addupto5serverfarmstoaweb‐cache.
• Optionallyspecifyanon‐standardportfortheredirectionofHTTPrequests.OutboundHTTP
requestsaredirectedtoport80bydefault. 
• CreatebypasslistscontainingarangeofhostwebsitesforwhichHTTP
requestsarenot
redirectedtothecacheserversforthisweb‐cache.SomewebsitesrequiresourceIPaddress
authenticationforuseraccess.HTTPrequestsforthesesitescannotberedirectedtothecache
servers.TWCBwillnotbeenabledforHTTPrequeststothesehostwebsiteswhenconfigured

asmembersofabypasslist.
•Specifytheend‐userswhoseHTTPrequestsareorarenotredirectedtothecacheserver.
End‐userspermittedredirectiontakepartinTWCB.End‐usersdeniedredirectiondonottake
partinTWCB.Allend‐usersarepermittedredirectionbydefault.
Note: The maximum number of bindings available should only be modified to assure availability to
functionalities that share these resources such as TWCB, NAT and LSNAT. It is recommended that
you consult with Enterasys customer support before modifying this value. See The TWCB Binding
on page 6 for a discussion on the TWCB binding.