ڷQAja NAT @wOҦջD~ALA쩳O NAT OHNAT O Network Address Translation ²gArWNOy}ǰezALDn\NObѤpqWeɤFC²檺ANAT \NOy IP ɾzI(GNAT D\۷hALAo̧ڭ̶ȻWeɪI)C
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NAT \
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ڭ̥ ¦ DAnsW Internet n㦳y@ IP (Public IP)z~Ap IP (Private IP) OઽP Internet iƷqCnFAѰ]zO@aqDޡAΪ̬O@ǮժTDAӥBzҭtd줺 20 qnFAo 20 qݭnsW Internet AåiHi Internet AȭnDAаݱzO_ݭnƦ 20 Ӥ@ IP OHpGun 20 Ӥ@ IP ܡAH̸g٪ӻAڭ̥iHӽ Seednet 512/64 (U/W) ADSL ACӱMuiH㦳 IP A]ڭ̦ 20 DAҥHNݭn|qܽuIȤFaIOuPӽ ADSL y{N|HYA󤣥λӽШ줧ٻݭnbC@qW]wBިqϥΩʡBi樾ru@AOηQANwgYjFA󤣥λڥh@.....
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ӭnOHoBͤwgQnhR IP ɾӤɺWeFI Linux O_F IP ɾ\IHMiHաINO NAT DO@oIڭ̦be Router ]wALѪFAʥ]ǰeDnOzLѪTAOApѬOઽP Internet qڡI] Linux @ Router ɡApG Linux DNOȦp IP A۵M]NLks Internet WhFC
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쩳ӦpOnHIoӮɭԴNon^Yͤ@ TCP ʥ]C ¦ `̭쪺 TCP ʥ][cAڭ̥iHo{ TCP ʥ]YӷPتa IP port Tb Header ̭ApGzLYǧ޳NAӧ TCP ʥ] header OHpGN TCP ʥ]ӷ IP ѥӪ Private IP ܦ Public IP ܡANiHs Internet FܡHIISSIͨ쭫IFINOo˰աINAT Dn\ध@NONӦۤ Client ݹqʥ] Header IP yˡz@ IP AӴ Client ݳsW Internet @ӤkI(GMաA IP ɾ]OϥΦP˪DzI)C Linux OΤFo˪\HٰOo²]w쪺 iptables aHIiptables iHiʥ]RAMAL٥iHiʥ]TקOIӬy{OpOHpUϩҥܡAڪϰ줺㦳 192.168.1.100 client n~suɭԡG
@ @
1. o client gateway ]w NAT DAҥHnsW Internet ɭԡAӫʥ]N|Qe NAT DաAoӮɭԪʥ] Header source IP 192.168.1.100 F
2. ӳzLo NAT DAo|N client ~suʥ] source  IP ( 192.168.1.100 ) ˦ ppp0 ( ]p )oӤҨ㦳@ IP oA]O@ IP FAҥHoӫʥ]NiHsW Internet FIP NAT DåB|Oгoӳsuʥ]Oѭ@ ( 192.168.1.100 ) client ݶǰeӪF
3. Internet ǰe^Ӫʥ]AM NAT DӱFAoӮɭԡA NAT D|hd߭쥻OѸTAñNؼ IP ppp0 W@ IP ^Ӫ 192.168.1.100 F
4. ̫h NAT DNӫʥ]ǰeoeʥ] Client oI
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pGOb iptables table AP NAT NO nat table POSTROUTING FINO²ϤEܷNI]NOAӫʥ]ugL NAT D iptables b IP PקѸTӤwAèSiJ NAT DաI ^_^IѤWTڭ̥iHD@ơANOGyz NAT Dܤֻݭn@Өp IP P@Ӥ@ IP ~zIӥBAyNAT DA@ӻA]O@ Router IzpG Router 䳣Op IP γO@ IP ɡALinux Dun Router \YiAYOO@Pp IP ɡA~ݭnH iptables ӱҰ NAT \C
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NAT \]iH²檺o˷QGyzbpHɨWɪɫJAޱzO_ULPQ}차WoDon@ӺʲzֵoPiCpGznN]}DWAnﱾ@ӦXkPCoɭԡAɨ(NAT)ۦkzˤ@ӴNOFCzIo˥iHAѤFܡH
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suܷNϡG
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ѤWzӥiHAѤFaHISAz NAT DWAܤֻݭnyzЪ`NAOyzӤOy馉dzIHҡAѩ󼷱| ppp0 oӼᲣͪA[W쥻A۵MNӥHWoIoӫܮeAѤFܡHUڥHdGup@suܷNϡAܩ@di NAT ϥܡANbݷ|oC

Ϥ@Bd NAT Dtm

bWϥܷAܲMaIڭ̪ Linux @馉dA@b ƾھ WA@b Hub/Switch WAåBH Hub/Switch sҦϰqAHզpIӤHOwo˪u觋աILAHHUҦnAӥBo˪p]oAXҦHAҥH٬OoAѤ@ULskInaA@UAiDz ^_^""
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֤ߪG
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ڭ̦b²]wNLFA֤߻POYA]NOG
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• Kernel 2.2.xx Gϥ ipchains ʥ]˪޳NF
• Kernel 2.4.xx Gϥ iptables ʥ]˪޳NI
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ҥHA٬OХJӪˬd@Uz֤ߪaI( uname -r ӹ)C²檺POkApGO Red Hat 7.0 ( t 7.0 )HeAϥΪO 2.2.xx ֤ߡA۵Mu ipchains ӤwAӦpGO Red Hat 7.1 ( t 7.1 ) H᪺AhϥΪO Kernel 2.4.xx A]̦nϥ iptables ޳NI] 2.4.xx IP BzҲշAjOw iptables ӧ@BznA ipchains Ҳդwgtb 2.4.xx YFIѩڬOH Red Hat 7.2, 7.3 P 9 @dҪAҥH۵MH iptables oIpGٷQnH ipchains Ӷi[] NAT B͡AѦҤ@UUogG
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• NAT AGhttp://vbird.org.cn/linux_server/redhat6.1/linux_22nat.php
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ֻݭn NAT []G
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ѫe NAT( Network Address Translation ) \शСAڭ̪DLiH@WeɪDAM]iH޲z@sb NAT D᭱ Client qIIҥH NAT \ܤ֦oⶵG
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• WeGڷQA[] NAT BͤjOƱiHFWeɪتIoO NAT D̤j\oI
• w@GxIw@ƧrIHOѤFA NAT PC su Internet WɡALܪ IP O NAT D@ IP AҥH Client ݪ PC MN㦳@w{תwFḬ_XHabi port scan ɭԡANz Client ݪ PC աIwhFI

NAT ]wiHϥΤ@dAM]iHϥΨdաIӤH٬OijϥΨdӧ㪺j}p쪺~A٬Ow@ǡIȤp쪺@ǰڡI ^_^
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@d NAT []G
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Wڭ̤wgLFAn[] NAT ܡAunyzNFAˤ@wݭnyd( NIC )zAOIҥHHKy觋(]֤F@drI)Ӥ NAT []IUOڭ̤Ъw˨BJG
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1. @ǨtΪAȪ port G

Fw_A٬Oˬd@UaIAڭ̻ݭnAѤ@Uڪ Linux D\άHIpGuOªn@ NAT ܡA Linux DҶ} port OVֶVnIiƱz}Fj@ӬPAN}lWWszۤvDLkH root nJF......C port kPܡytΤ@wݭnAzЦb suf ̭wgܲMFIڥH Red Hat 9 ӻG

1. ϥ ntsysv ]w}ɱҰʪAȶءG [root@test root]# ntsysv unܩUXӪAȧYiG atd, cron, iptables, keytables, network, random, syslog, xinetd 2. s}]wͮġG [root@test root]# reboot 3. [ثe port }Ҧh֭ӡH [root@test root]# netstat -an | more Active Internet connections (servers and established) Proto Recv-Q Send-Q Local Address           Foreign Address         State Active UNIX domain sockets (servers and established) Proto RefCnt Flags       Type       State         I-Node Path unix  7      [ ]         DGRAM                    944    /dev/log unix  2      [ ]         DGRAM                    3162963 unix  2      [ ]         DGRAM                    739227 unix  2      [ ]         DGRAM                    739189 unix  2      [ ]         DGRAM                    1070 unix  2      [ ]         DGRAM                    953 unix  2      [ ]         STREAM     CONNECTED     690 # `NGɶqnݨ즳 LISTEN NNI̦hNO ssh NnFIDzLAȡI

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2. utmG

w˳suOHֶRuӬ[]aIѩ Linux Du@idAҥHҦ˸m(]A Linux D, client ݹq, ƾھ)ݭnb Hub/Switch WAIUˤlG
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ϤGB@d NAT Dtm @
oӮɭԽЯSOdNաIpGOϥ ADSL ܡAb Linux DWӷ|w rp-pppoe oӪFAåBb| ppp0 oӺAPɤnѤFAҰʺdɭԤONwg eth0 oӹɭ]wܡHAKKIڭ̤ONӺFܡHISINOoˡIOApGO Cable Ϊ̬OLTwkܡAoӤ]thաILѩ Cable 觋S۰ʲͨӥHWɭAҥHNݭn]w IP Alias oA]NO eth0:0 աIYNOH eth0 eth0:0 oӤӳsuoIϥAu@idA]iHi NAT աI ^_^""
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3. ]wG

ڭ̤OHB Cable ΩTw IP ҰաI
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ADSL G
biJ Linux ñҰʺdAڭ̷|o eth0 oӬɭAA[W᪺ ppp0 ɭAҥHڭ̴Nwg|ӨAOO ppp0, eth0I~Aڹwpp쪺 IP 192.168.1.0/24 o C Class A𫟺A Linux NAT Dp IP ܬ 192.168.1.2 o@ӡI
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• Ĥ@Ӻ -- ppp0 -- ]wGoӪFӤaINOڭ̦b sW Internet @Y쪺 rp-pppoe W觋C

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• d -- eth0 -- ]wGЪ`NApGznPɨϥ ppp0 eth0 AЦbeҰ eth0 aIHo eth0 oӺɭ]wI( GpGzDp]wܡANзӧڪ觋ӶgYi )G

[root@test root]# vi /etc/sysconfig/network-scripts/ifcfg-eth0 DEVICE=eth0 BOOTPROTO=static BROADCAST=192.168.1.255 IPADDR=192.168.1.2 NETMASK=255.255.255.0 NETWORK=192.168.1.0 ONBOOT=yes <==nabo̡Iг]w yes I # pGzoӦp]wܡANӤWNnFI

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Cable BʦG
b Cable pSӬۦPFIoӮɭԥuAOO eth0, eth0:0 oI]wG
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• d -- eth0 -- ]wGЪ`NAѩ cable ϥΪO DHCP DAҥHoӮɭԽЯSOdNzU]wI( GpGzDp]wܡANзӧڪ觋ӶgYi )G

[root@test root]# vi /etc/sysconfig/network-scripts/ifcfg-eth0 DEVICE=eth0 BOOTPROTO=dhcp <==o̳̭nI BROADCAST=192.168.100.255 IPADDR=192.168.100.1 NETMASK=255.255.255.0 NETWORK=192.168.100.0 ONBOOT=yes # pGzoӦp]wܡANӤWNnFI

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• --eth0:0 ]wGb IP Alias ]wAڭ̤wgb Router LhFIаȥ^ӳ`A\Ū@ApGzOop]wzܡI

[root@test root]# vi /etc/sysconfig/network-scripts/ifcfg-eth0:0 DEVICE=eth0:0 BOOTPROTO=static BROADCAST=192.168.1.255 IPADDR=192.168.1.2 NETMASK=255.255.255.0 NETWORK=192.168.1.0 ONBOOT=yes  # pGzoӦp]wܡANӤWNnFI

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Tw IP pG
cable ]wXG@Ҥ@ˡAuӤAOO eth0, eth0:0AݭnSO`NO eth0 oӪFAznygT IP, netmask, network, broadcast ӥB ONBOOT=yes ~iHIzA eth0:0 hPWۦPI
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Ұʨp쪺 IP G
ҰʤᶶK[@UѪTI

[root@test root]# ifdown eth0 [root@test root]# ifup   eth0 [root@test root]# route Kernel IP routing table Destination     Gateway         Genmask         Flags Metric Ref    Use Iface swks81-1.adsl.s *               255.255.255.255 UH    0      0        0 ppp0 192.168.1.0     *               255.255.255.0   U     0      0        0 eth0 127.0.0.0       *               255.0.0.0       U     0      0        0 lo default         swks81-1.adsl.s 0.0.0.0         UG    0      0        0 ppp0 # KKIo˴NO\աI`NAWoӸѬOH adsl ҪI

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4. ]wLɮG

٦@Ǻɮ׭n]wI/etc/hosts, /etc/resolv.conf, /etc/sysconfig/network,
OѤFڭ٦Lɮ׭n]wIܭnG

1. Np IP [J /etc/hosts ̭haI [root@test root]# vi /etc/hosts 127.0.0.1     localhost 192.168.1.1   linux001 192.168.1.2   linux002 .......()...... 192.168.1.100 linux100 .......()...... 192.168.1.254 linux254 2. N DNS IP g /etc/resolv.conf ̭hAo̥HعqH Seednet [root@test root]# vi /etc/resolv.conf nameserver 168.95.1.1 nameserver 139.175.10.20 3. ]wDWٸ gateway P_G [root@test root]# vi /etc/sysconfig/network NETWORKING=yes HOSTNAME=your.domain.name <==gzDW GATEWAY= <==DzOTwAMoӤnJFI

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5. ]p NAT shell scripts G

N@ǫOgb scripts YְաITpUAثez Linux DWӬOwgiH`~su~IӥB]wgiHTsu\F~IpG٨S\ܡAл֦A ϰ]w Yhd@dƥhInFAۤUӥun@ӵ{AKKINiHN NAT ҰʳIoӴNnFI]򥻤WAڭ̨ϥΪO iptables oӪFA۵MNݭno ip_tables ҲդFIӬdݼҲջPJҲժOO lsmod, modprobe InFAziHbROܦrUiu@G

echo "1" > /proc/sys/net/ipv4/ip_forward modprobe ip_tables modprobe ip_nat_ftp modprobe ip_nat_irc modprobe ip_conntrack modprobe ip_conntrack_ftp modprobe ip_conntrack_irc /sbin/iptables -F /sbin/iptables -X /sbin/iptables -Z /sbin/iptables -F -t nat /sbin/iptables -X -t nat /sbin/iptables -Z -t nat /sbin/iptables -P INPUT   DROP /sbin/iptables -P OUTPUT  ACCEPT /sbin/iptables -P FORWARD ACCEPT /sbin/iptables -t nat -P PREROUTING  ACCEPT /sbin/iptables -t nat -P POSTROUTING ACCEPT /sbin/iptables -t nat -P OUTPUT      ACCEPT /sbin/iptables -t nat -A POSTROUTING -o ppp0 -s 192.168.1.0/24 -j MASQUERADE

ٰOoڭ̦b²]w̭Ѥ@ script aH script W iptables.rule A script PɥiH NAT \I㪺 script Ыeӳ`[ݡAo̳ȥH ADSL NAT DҨӤлݭn諸aG

[root@test root]# cd /usr/local/virus/iptables [root@test iptables]# vi iptables.rule #!/bin/bash #...()... # ]w~  EXTIF="ppp0" # ]w鷺Pp쪺]w  INIF="eth0"   INNET="192.168.1.0/24"        # This is for NAT's network #....()....   if [ "$INIF" != "" ]; then         /sbin/iptables -A INPUT -i $INIF -j ACCEPT         echo "1" > /proc/sys/net/ipv4/ip_forward         /sbin/iptables -t nat -A POSTROUTING -s $INNET -o $EXTIF -j MASQUERADE   fi #...()...

o{Aunק EXTIF INIF Pܤk (INNET) AAǥѳ̫᭱@]w(MASQUERADE)\AI NAT Hΰ򥻪D@Nwg OK oI۷²aIԲӪ iptables.rule wˤkAЩe½²]whdwI^_^IpGL~ANiHNo script gbz /etc/rc.d/rc.local ̭oI
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6. Client ݪ]wѼG]tO]wѼƦӤwIoӵ@Uڭ̦bΤݳ]wAI
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d NAT []G
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uOAoӳsu[]b ϰsu wgLܦhMFIo̤AƪIȦCXXӭnaA򥻤WA@id]w觋XGۦPAuO eth0:0 ܦF eth1 ӤwաI]wG
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• eth0 鷺dA㦳p IP A IP 192.168.1.2 C
• eth1 ~dAQΨӶi ADSL AҥH}ɭԤn]w on I
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P˪Aڭ̪]w觋G
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1. @ǨtΪAȪ port GPe@`ۦPI

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2. utmGPϤ@tmۦPC

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3. ]wG

nabw˲ĤGdIw˺dޥЫe sW Internet ѦҡILAĤGdwˡAbo̦ǫijG򥻤WAĤGid̦nΨϥλPĤ@iۦPdAҦpzĤ@idϥ RTL 8139AĤGid̦nϥΧOdC]go{Ab RedHat 6.1 ^媩Aw˨ۦP ( PqX )  RTL8139 AGMidXJOgѲĤ@iI]NOAĤGidڥNSγBIåBA]ܮeo eth1 P eth0 pIҥHAаOoAyĤGidɶqnϥλPĤ@idۦPdIzMAznϥΦP@Ӵd]OiHաIثeڪWNOϥΨ RTL8139 dCLAbw˪ɭԽЯSOdNAnPɦwA̦nO@w˧AAw˥t@I|n@IաIw˪BJiHO(Ъ`NAڥH ADSL ҪA𫟺A eth0 鷺A eth1 ~AШ̷ӱz]wӭץOI)G
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• BwwGoӤΦAFaIAAM}~ߡAJPCIdYiF
• }Bw鱽GMA}Aө}L{Az Linux |Dʥho@id]pGoidOQ Linux 䴩I^F
• w˺dXʵ{GpGbW@BJAzdäQAN˸IШsW Internet ѦҺdXʵ{wˤk
• ˵]w /etc/sysconfig/network-scripts/ifcfg-eth1Gbw˧FdXʵ{Ab /etc/sysconfig/network-scripts/ Aӷ| ifcfg-eth1 o@ɮסCг]wLaI]O~dAڳo̰]LOQ ADSL AҥHiHOoˡG

[root@test root]# vi /etc/sysconfig/network-scripts/ifcfg-eth1 DEVICE=eth1 BOOTPROTO=static BROADCAST=192.168.0.255 IPADDR=192.168.0.2 NETMASK=255.255.255.0 NETWORK=192.168.0.0 ONBOOT=no <==o̫ܭnI~ΨӼdnb}ɭԱҰʰաI

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o˴N\oI²aI ^_^""
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4. ]wLɮG

L@Ǻɮפ]n]wIY/etc/hosts, /etc/resolv.conf, /etc/sysconfig/network,]w觋e@p`ۦPI
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5. ]p NAT shell scripts G

򥻤WA]w觋W]O@Ҥ@˪աIz¥iHȨϥΫe@p` script Ӷi NAT ]wAuOn`NӲr]wApGzڪpPANݭnק@UաI U script aI
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[ѸTG
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b NAT ]wA̸g媺~suTӦ۩ ѸT ~աIoӦbڭ̪ sW Internet  峹wgLFALAڭ̳o̦A@UIKozSǤFP˪~FIѩbisɭԡA|wҿת router Ϊ̬O gateway ]wADOӦ۩s줧suCӧڭ̦b]wɡA``|ǤF@ӿ~ANOwF Gateway FIбzѦҤ@UsW Internet @]w觋Ab ADSL Cable suɡAСyȥzn]w gateway ~nI
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AӡAб`UF route O[@Uz linux Dѳ]wO_TI

b Client ݪ]wuO²檺iHFIѩڭ̤W]wO 192.168.1.0/24 o C Class pAҥHzunOoXƱG

1. network ]wݭnG 192.168.1.0
2. broadcast ]wݭnG 192.168.1.255
3. netmask ]wݭn 255.255.255.0
4. IP ]wݭn 192.168.1.1 ~ 192.168.1.254 @ABy୫ơz
5. Gateway Ϊ̻O qTh ݭn]wz Linux 鷺 IP AHڪҤlӻANO 192.168.1.2 I
6. DNS ]wGoӳ̮eXFAz DNS ]wݭnOz ISP z DNS IPApGzDܡAiHJ 168.95.1.1 o@ӤعqH DNS Ϊ̬O 139.175.10.20 o@ SeedNet DNS YiIdUn]w 192.168.1.2 I|sXhI

jPWNOo˰աIܩ Client ݳq`O Windows A]wiHeѦҤ@Uϰ]w@Iܩ Linux ݫhݭndݤ@U sW Internet ̭Tw IP ]wաI

Ъ`NAboӨҤlAڭ̨èSϥΨʥ]Rʧ@Au IP ˦ӤwAҥHG

• Client ݨӻAѩwggLF IP ˪\AҥH򥻤WAzqL NAT DsXhʥ] IP |Oy NAT D~@ IP zA]󤺳 Client ݦӨAѩ Cracker XGOھ IP Ӷi}aAӦ]zsXhʥ] IP O NAT D@ IP A۵Mz Client ݴNwhFI򥻤WA Client ݦb NAT ASwn]٦nAOyrn@wnwIz]z|qllrAҥH٬Oi|rաII

• Server ݨӻAڭ̶ȶȳ]w@²檺WhAӥBb쥻 iptables.rule ٹw]}ҤF\hfAҥHo˪@ӥDäOQwA]Az̦n٬OۦN iptables.rule ̫᭱XӶ}񪺰fLѱ~noI(pGz NAT DȷQntdWeɪ\઺ܡI)

• ²檺 NAT Dγ~PB@zC
• ]ڬOzqWhDޡAڪDڭ̳줺@ 100 q (Windows @~t)A𫟺@jAojƬOۿWߪAåBjU۾֦@ Linux Dbtdɮפɪu@(NOӷ|ͨ쪺 SAMBA D)CLAڭ̤qȦ@~ ADSL V 512 MuӤwC{bAکROzWq 100 qiHsW Internet AӥBuhz@ Linux DAåB즳 Linux D\ ( NO SAMBA ) ٬OsbCаݡG
1. qWܷNϬH
2. hXӪ@ Linux Dγ~ ADSL sPpsA Linux ѼƬH
3. ⳡ Linux SAMBA DѼƬH
4. ӳѼƽЦۦ]w
eѦҸѵ