Specifications

How Can I Implement TWCB?
April 16, 2009 Page 2 of 14
whomwebcachingisnotde siredtoahostredirectionlist,denyingtheseusersaccessto
TWCBfunctionality.
•Instandardwebcaching,auser‐cacheisconfiguredandassignedtoasinglecacheserver.
TWCBprovidesforloadbalancingacrossallcache‐serversofagivenserverfarmthatcanbe
configuredforheavyweb‐usersusingapredictorround‐robinalgorithm.
• Scalabilityisprovidedbytheabilitytoassociateupto128cache‐serverswiththeweb‐cache.
Thisscalabilityisfurtherrefinedbytheabilitytologicallyassociatecache‐serverswithupto5
serverfarms.
How Can I Implement TWCB?
ImplementingTWCBrequiresaroutednetworkwithIPinterfacesthatallowtheN‐Seriesrouter
tosendrequestsfortheinternettothecorrectwebcachingdevice.
TherearefiveaspectstoTWCBconfiguration:
• Createtheserverfarmsthatwillcachethewebobjectsandpopulatethemwithcache‐servers.
• Optionally
associateheavyweb‐userswitharound‐robinlistwhichcachesthoseusers’web
objectsacrossallserversassociatedwiththeconfiguredserverfarm.
• OptionallyspecifythehostswhoseHTTPrequestswillorwillnotberedirectedtothe
cache‐servers.
• Createaweb‐cachethattheserverfarmswillbe
associatedwith.
•Applythecachingpolicytoanoutboundinterface,toredirectHTTPtrafficonthatinterfaceto
thecache‐servers.
TWCB Overview
ATWCBconfigurationismadeup ofoneormorecache‐serversthatarelogicallygroupedina
serverfarmandoneormoreserverfarmsthatare associatedwithaweb‐cache.ThecurrentTWCB
implementationsupportsasingleweb‐cache.
Figure 1onpage 3providesanoverviewofaTWCB
configuration.Inouroverview,Cache1isthe
nameoftheweb‐cache.Itismadeupoftwoserverfarms:s1Serverands2Server.Thes1Server
serverfarmisconfiguredwith2cache‐serversfromthe186.89.0.0subnet.Thes2Serverserver
farmisconfiguredwith5cache‐serversfromthe176.89.0.0subnet.
Webobjectsforeachend‐user
arecachedonacacheserver.
Notes: TWCB is currently only supported for N-Series products.
TWCB is an advanced routing feature that must be enabled with a license key. If you have
purchased an advanced license key, and have enabled routing on the device, you must activate
your license as described in the configuration guide that comes with your Enterasys Matrix DFE or
NSA product in order to enable the TWCB command set. If you wish to purchase an advanced
routing license, contact Enterasys Networks Sales.
A minimum of 256 MB of memory is required on all modules in order to enable TWCB. See the
SDRAM field of the show system hardware command to display the amount of memory installed
on a module. Module memory can be upgraded to 256 MB using the DFE-256MB-UGK memory kit.