Specifications

NAT Overview
September 08, 2010 Page 8 of 18
DNS, FTP and ICMP Support
NATworkswithDNSbyhavingtheDNSApplicationLayerGateway(ALG)translateanaddress
thatappearsinaDomainNameSystemresponsetoanameorinverselookup.
NATworkswithFTPbyhavingtheFTPALGtranslatetheFTPcontrolpayload.BothFTPPORT
CMDpacketsandPASVpackets,
containingIPaddressinformationwithinthedataportion,are
supported.TheFTPcontrolportisconfigurable.
TheNATimplementationalsosupportsthetranslationoftheIPaddressembeddedinthedata
portionoffollowingtypes ofICMPerrormessage:destinationunreachable(type3),sourcequench
(type4),redirect(type5),timeexceeded(type11)
andparameterproblem(type12).
NAT Timeouts
Themaximumtimeoutvalueinsecondsperflowisconfigurableforthefollow ingflowtypes:
• Dynamictranslation
•UDPandTCP
•ICMP
•DNS
•FTP
NAT Router Limits
Routerparameterssuchasthenumberofbindingsandcachesizeusevaluablememoryresources
thataresharedbyotherroutingfunctionssuchasLSNATandTWCBonafirst‐comefirst‐served
basis.Bydefaultthesesettingsaresettomaximumvalues.Byloweringthemaximumlimitfor
affectedparameters,
theresourcedeltabetweenthenewlimitandthemaximumvalueforthat
parameterwillbeavailabletootherroutingfunctionssuchasLSNATandTWC B.Maximum
limitscanbesetorclearedforthefollowingNATrelatedrouterparameters:
•NATbindings
•Cachesize
• Dynamicmappingconfigurations
•Staticmappingconfigura tions
•Interfaceconfigurations
•Global
Addressconfigurations
•Globalportconfigurations
Note: The maximum number of bindings and cache 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 these parameter
values.