Specifications

LSNAT Overview
September 8, 2010 Page 7 of 28
Ping
Realserverfailuredetectioncanbeconfiguredforpingonly.Inthiscase,therealserverispinged
beforeasessioniscreated.
TCP/UDP Port Service Verification
TCPportserviceverificationcanbeenabledononeormoreloadbalancingservers.Aconnect
requestissentouttotheserverport.IftheconnectrequestsucceedsthenLSNATknowstheserver
isup.YoucanconfigureTCPfailuredetectionforbothpingandTCPportserviceverification.
UPD
portserviceverificationcanbeenabledononeormoreloadbalancingservers.LSNAT
accomplishesthisbysendingaUDPpacketwith“\r\n”(CarriageReturn/LineFeed)asdatato
theUDPport.IftheserverrespondswithanICMP“PortUnreachable”message,itisconcluded
thattheportis
notactiveandtheserverisreportedas“DOWN”.Otherwise,iftheLSNATrouter
eithergetsdataback fromtherequesttotheserverordoesnotgetanyresponseatall,itis
assumedthattheportisactiveandtheserverisreportedas“UP”.Thelackof
aresponsecould
alsobetheresultoftheserveritselfnotbeingavailableandcouldproduceanerroneousindication
oftheserverbeing“UP”.ToavoidthiswhenrequestingaUDPapplicationonaUDPport,an
ICMPpingisissuedfirsttoensurethattheserverisavailablebefore
submittingtheUDP
applicationrequest.
Application Content Verification
ApplicationContentVerification(ACV)canbeenabledonaporttoverifythecontentofan
applicationononeormoreloadbalancingservers.ACVisamethodofensuringthatdatacoming
fromyourserversremainsintactanddoesnotchangewithoutyourknowledge.ACVcan
simultaneouslyprotectagainstserver
outages,accidental filemodificationordeletion,andservers
whosesecurityhasbeencompromised.Byitsnature,ACVisprotocol‐independentandis
designedtoworkwithanytypeofserverthatcommunicatesviaformattedASCIItextmessages,
includingHTTP,FTP,andSMTP.ForACVverification,youspecifythefollowing :
•Astring
thattheroutersendstoasingleserver.ThestringcanbeasimpleHTTPcommandto
getaspecificHTMLpage,oritcanbeacommandtoexecuteauser‐definedCGIscriptthat
teststheoperationoftheapplication.
•Thereplythattheapplicationoneachserversends
backisusedbytheroutertovalidatethe
content.InthecasewhereaspecificHTMLpageisretrieved,thereplycanbeastringthat
appearsonthepage,suchas“OK”.IfaCGIscriptisexecutedontheserver,itshouldreturna
specificresponse(for
example,“OK”)thattheroutercanverify.
ACVworksbysendingacommandtoyourserverandsearchingtheresponseforacertainstring.
Ifitfindsthestring,theserverismarkedasUp.Ifthestringisnotfound,the serverismarkedas
Down.
Forexample,ifyou
sentthefollowingstringtoyourHTTPserver,“HEAD/
HTTP/1.1\\r\\nHost:www.enterasys.com\\r\\n\\r\\n”,youcouldexpecttogetaresponseof
areturnedstringsimilartothefollowing:
HTTP/1.1 200 OK
Date: Tue, 11 Dec 2007 20:03:40 GMT
Server: Apache/2.0.40 (Red Hat Linux)
Last-Modified: Wed, 19 Sep 2007 13:56:03 GMT
ETag: “297bc-b52-65f942c0”
Accept-Ranges: bytes
Content-Length: 2898