Chapter15NetworkLayerDetection
R2(config)#interfacegei-1/1
R2(config-if-gei-1/1)#ipaddress10.1.1.2255.255.255.0
R2(config-if-gei-1/1)#noshutdown
R2(config-if-gei-1/1)#ipforwardunreachable
R2(config-if-gei-1/1)#exit
R2(config)#icmp-config
R2(config-icmp)#interfacegei-1/1
R2(config-icmp-if-gei-1/1)#ipunreachable
R2(config-icmp-if-gei-1/1)#exit
lConīægurationVeriīæcation
R2doesnothavearouteto1.2.3.4/32.
RunthedebugipicmpdetailcommandonR2.Runtheping1.2.3.4commandon
R1.YoucanseethatR2sendshostunreachablepacketstoR1.
15.5ConīguringIPPing
Overview
lDescriptionofPing
Pingoriginatesfromsonarlocationoperation.Pingisusedtotestwhetheranother
hostisreachable.TheprogramsendsanICMPEchoRequesttothehostandwaits
foranICMPEchoReply.
Ifahostcannotbepingedsuccessfully,thehostcannotbeloggedinthrough
TelecommunicationNetworkProtocol(TELNET)orFTP .Onthecontrary,ifahost
cannotbeloggedinthroughTELNET,thepingprogramcanbeusedtoīændoutthe
problem.Thepingprogramalsocanbeusedtotestthetimeofaround-triptothe
host,whichindicateshowfarawaythehostis.
lCharacteristicsofPing
ThepingcommandsendsanICMPEchoRequest.Ifthedestinationreceivesthe
ICMPEchoRequest,itwillsendanICMPEchoReplytothesourceaddressofthe
EchoRequest.Therefore,thepingcommandcanbeusedtodiagnosenetwork
connectivityfaults.
ThepingprogramthatsendsanEchoRequestiscalledaclient,andthehostthat
ispingediscalledaserver.ThekernelsofmostTransferControlProtocol/Internet
Protocol(TCP/IP)functionssupportapingserverdirectly.Theserverisnotauser
process.
TheformatofanICMPEchoRequestandanICMPEchoReplyisshowninFigure
15-6.
15-9
SJ-20140504150128-007|2014-05-10(R1.0)ZTEProprietaryandConīædential