ÿØÿà JFIF 

  
 
  ÿÛ „ 	 ( %"1!%)+...383,7(-.+




-+++--++++---+-+-----+---------------+---+-++7-----ÿÀ  ß â
" 

ÿÄ   

           
 ÿÄ H 
     
 !1AQaq"‘¡2B±ÁÑð#R“Ò Tbr‚²á3csƒ’ÂñDS¢³$CÿÄ 
 


            
ÿÄ %

 
       
!1AQa"23‘ÿÚ 
  ? ôÿ ¨pŸªáÿ —åYõõ\?àÒü©ŠÄï¨pŸªáÿ —åYõõ\?àÓü©ŠÄá 0Ÿªáÿ Ÿå[úƒ	ú®ði~TÁb
qÐ8OÕpÿ ƒOò¤Oè`–RÂáœá™êi€ßÉ< FtŸI“öÌ8úDf´°å}“¾œ6
öFá°y¥jñÇh†ˆ¢ã/ÃÐ:ªcÈ
"Y¡ðÑl>ÿ ”ÏËte:qž\oäŠe÷󲍷˜HT4&ÿ ÓÐü6ö®¿øþßèô	Ÿ•7Ñi’•j|“ñì>b…þS?*Óôÿ ÓÐü*h¥£ír¶ü UãSç‚Ÿ[AÐaè[ûª•õ&õj?†Éö+EzP—WeÒírJFt	‘BŒ†Ï‡%#tE Øz ¥OÛ«!1›üä±Í™%º<!vB™'èÔ6´Ña¿«e`Àà0U[-ÂБ4)M÷YK*³hï÷%ÎÎkÇ«m‘-íWŽLsã?nÂ~«†üö®þ¡ÂlÃaÿ ‰ÿ l©°Õ¥ åÜá¿r ºL[Çâ°(Çè'Vãôl8´ÏRÀvLvPõ:…ÙNçF™÷ë>Íãö]°î(–:@<‹ŒÊö×òÆt¦ãº+‡¦%ÌÁ²h´OƒJŒtMÜ>ÀÜÊw3
Y´•牋4ǍýʏTì>œú=Íwhyë,¾Ôò×õ¿ßÊa»«þˆѪQ|%6ž™A	õ%:øj<>É—ÿ Å_ˆCbõ¥š±ý¯Ýƒï…¶|RëócÍf溪“t.СøTÿ *Ä¿-{†çàczůŽ_–^XþŒ±miB[X±d 1,é”zEù»&
î9gœf™9Ð'.;—™i}!ôšåîqêÛ٤ёý£½ÆA–àôe"A$˝Úsäÿ 
÷Û	#°xŸëí(l
	 »ý3—¥5m!
rt`†0~'j2(]S¦¦kv,ÚÇl¦øJA£Šƒ
J3E8ÙiŽ:cÉžúeZ°€¯\®kÖ(79«Ž:¯X”¾³Š&¡* ….‰Ž(ÜíŸ2¥ª‡×Hi²TF¤ò[¨íÈRëÉ䢍mgÑ.Ÿ<öäS0í„ǹÁU´f#Vß;Õ–…P@3ío<ä-±»Ž.L|kªÀê›fÂ6@»eu‚|ÓaÞÆŸ…¨ááå>åŠ?cKü6ùTÍÆ”†sĤÚ;H2RÚ†õ\Ö·Ÿn'¾ ñ#ºI¤Å´%çÁ­‚â7›‹qT3Iï¨Ö
Ú5I7Ë!ÅOóŸ¶øÝñØôת¦$Tcö‘[«Ö³šÒ';Aþ ¸èíg
A2Z
"i¸vdÄ÷.iõ®§)¿]¤À†–‡É&ä{V¶iŽ”.Ó×Õÿ û?h¬Mt–íª[ÿ Ñÿ ÌV(í}=ibÔ¡›¥¢±b
 Lô¥‡piη_Z<‡z§èŒ)iÖwiÇ 2hÙ3·=’d÷8éŽ1¦¸c¤µ€7›7Ø	ð\á)}	¹fËí›pAÃL%âc2 í§æQz¿;T8sæ°qø)QFMð‰XŒÂ±
N¢aF¨…8¯!U		Z©RÊ ÖPVÄÀÍin™Ì-GˆªÅËŠ›•zË}º±ŽÍFò¹}Uw×#ä5B¤{î}Ð<ÙD
é©¤&‡ïDbàÁôMÁ."
¤‡ú*õ'VŽ|¼´Úgllº¼klz[Æüï÷Aób‡Eÿ dÑ»Xx9ÃÜ£ÁT/`¼¸vI±Ýµ·Ë‚“G³þ*Ÿû´r|*}<¨îºœ @¦mÄ’M¹”.œ«Y–|6ÏU¤jç¥ÕÞqO
˜kDÆÁ¨5ÿ š;Њ¦¦€GÙk \
	–Þ=â¼=SͧµªS°ÚÍpÜãQűÀõ¬?ÃÁ1Ñ•õZà?hóœ€
L¦l{Y*K˜Ù›zc˜–ˆâø+¾	­-Ök¥%ùEÜA'}ˆ><ÊIè“bpÍ/qÞâvoX€w,\úªò6Z[XdÒæ­@Ö—€$òJí#é>'°Ú
ôª˜<)4ryÙ£|óAÅn5žêŸyÒäMÝ2{"}‰–¤l÷ûWX\l¾Á¸góÉOÔ /óñB¤f¸çñ[.P˜ZsÊË*ßT܈§QN¢’¡¨§V¼(Üù*eÕ“”5T¨‹Âê¥FŒã½Dü[8'Ò¥a…Ú¶k7a
*•›¼'Ò·\8¨ª\@\õ¢¦íq+DÙrmÎ…_ªæ»ŠÓœ¡¯’Ré9MÅ×D™lælffc+ŒÑ,ý™ÿ ¯þǤ=Å’Á7µ÷ÚÛ/“Ü
€ñýã¼àí¾ÕÑ+ƒ,uµMâÀÄbm:ÒÎPæ{˜Gz[ƒ¯«® KHà`ßØŠéí¯P8Aq.C‰ à€kòpj´kN¶qô€…Õ,ÜNŠª-­{Zö’æû44‰sŽè‰îVíRœÕm"
6?³D9¡ÇTíÅꋇ`4«¸ÝÁô ï’ýorqКÇZ«x4Žâéþuïf¹µö[P ,Q£éaX±`PÉÍZ ¸äYúgüAx
’6Lê‚xÝÓ*äQ
Ï’¨hÍ
=²,6ï#rÃ<¯–£»ƒ‹,–ê•€ aÛsñ'%Æ"®ÛüìBᝠHÚ3ß°©$“XnœÖ’î2ËTeûìxîß
¦å¿çÉ
ðK§þ{‘t‚Ϋ¬jéîZ[”š7L¥4VÚCE×]m¤Øy”ä4-dz£œ§¸x.*ã
ÊÊ b÷•h:©‡¦s`BTÁRû¾g⻩‹jø sF¢àJøFl‘È•Xᓁà~*j¯ +(ÚÕ6-£¯÷GŠØy‚<Ç’.F‹Hœw(+)ÜÜâÈzÄäT§FߘãÏ;DmVœ3Àu@mÚüXÝü•3B¨òÌÁÛ<·ÃÜz,Ì@õÅ·d2]ü8s÷IôÞ¯^Ç9¢u„~ëAŸï4«M?
K]­ÅàPl@s_ p:°¬ZR”´›JC[CS.h‹ƒïËœ«Æ]–÷ó‚wR×k7X‰k›‘´ù¦=¡«‰¨¨Â')—71ó’c‡Ðúµ
`é.{§p¹ój\Ž{1h{o±Ý=áUÊïGÖŒõ–-BÄm+AZX¶¡
ïHðæ¥JmÙ;…ä¡Ÿˆ¦ ° äšiÉg«$üMk5¤L“’çÊvïâï	,=f“"íἊ5ô¬x6{ɏžID0e¸vçmi'︧ºð9$ò¹÷*£’9ÿ ²TÔ…×>JV¥}Œ}$p[bÔ®*[jzS*8
”·T›Í–ñUîƒwo$áè=LT™ç—~ô·¤ÈÚ$榍q‰„+´kFm)ž‹©i–ËqÞŠ‰à¶ü( ‚•§ •°ò·‡#5ª•µÊ﯅¡X¨šÁ*F#TXJÊ
ušJVÍ&=iÄs1‚3•'fý§5Ñ<=[íÞ­
PÚ;ѱÌ_~Ä££8rÞ
²w;’hDT°>ÈG¬8Á²ÚzŽ®ò®qZcqJêäÞ-ö[ܘbň±çb“Š¶31²n×iƒðÕ;1¶þÉ
ªX‰,ßqÏ$>•î íZ¥Z 1{ç൵+ƒÕµ¥°T$§K]á»Ûï*·¤tMI’ÂZbŽÕiÒ˜}bÓ0£ª5›¨[5Ž^ÝœWøÂÝh°
¢OWun£¤5 a2Z.G2³YL]jåtì”
ä	ÁÓ‘%"©<ÔúÊ°sº UZvä‡ÄiÆÒM .÷V·™ø#kèýií<NçŽôª¦„lË»{ƒ®<
[¦Y‹éƒ}j•*‚±€I‡e&gbéšp9å^!®€ö?ù^àTzo@Q¨Aêœ& [”…üÔ}пF’Hq‚©´{“ëH·?.½%úå»É Á´9¿¼Ò‰Á¼Ì¥Ús¼zW¶aÃhwÖ…ÑÏ$mò´ë:×Ñγ|”x§
µ0Âз$·aÆn µ†šÇ³£‰Ì®ž
õ@kŽ«gtí䢩ÒP×5¤?µÿ m´Ì^ ‡8¸Á8‹”žÆWÑ ¡™„,Ì“»à‹ÃéV¸®á›ÐÇŽBÀ®Ã…Z”ØÛë8;é|Ñ5)7aÕ&2Ù¸÷©ö—Ð;‡¬7"¿"7M·d
ñœÒÌf5”ê ;"Ãp5¯¬3‹ùJÚÝG›½&¯<{òñKÎÖ“3:¦ÀòGPÅS¨;
à‘Ün´öpð±W)z'¬öÀÖ#Xf2& æ
Œ‹é¾"‹\!Ñ9…
0±2A›*ØMÄ $X
끫ØXÖ,X¥ ô'ËnFÍãlqJXçuaJ4¦„ëµ7ê;h"Zã¾Áä£,vÛ‹’N©E(Öu÷)…ÁaÜÇÔkˆ$‘1kmG¨øtÛ>Ì–ª)µT[)BˆõÑ
xB¾B€ÖT¨.¥~ð@VĶr#¸ü*åZNDŽH;âi 
],©£öØpù(šºãö¼T.uCê•4@ÿ GÕÛ)Cx›®0ø#:ÏðFÒbR\(€€Ä
®fã4Þ‰Fä¯HXƒÅ,†öEÑÔÜ]Öv²?tLÃvBY£ú6Êu5ÅAQ³1‘’¬x–HŒÐ‡ ^	¸KwJôÖŽ5×CÚ¨vÜ«/B0$×k°=ðbÇ(Ï)w±A†Á†	11Í=èQšµ626ŒÜ/`G«µ<}—-Ö7KEHÈÉðóȤmݱû±·ø«Snmá=“ä«šmݱŸ¡¶~ó·“äUóJæúòB|E LêŽy´jDÔ$G¢þÐñ7óR8ýÒ…Ç›	WVe#·Ÿ	p·Fx~•ݤF÷0Èÿ K¯æS<6’¡WШ
;´ÿ ¥Êø\Òuî†åÝ–VNœkÒ7oòX¨Á­Ø÷FÎÑä±g÷ÿ M~Çî=p,X´
ÝÌÚÅ‹
’ÃjÖ.ØöÏñ
qïQ¤ÓZE†° =6·]܈ s¸>v•Ž^Ý\wq9r‰Î\¸¡kURÒ$­*‹Nq?Þª*!sŠÆ:TU_u±T+øX¡
®¹¡,ÄâÃBTsÜ$Ø›4m椴zÜK]’’›Pƒ@€#â˜`é¹=I‡fiV•Ôî“nRm+µFPOhÍ0B£
€+¬5c
v•:P'ÒyÎ ‰V~‚Ó†ÖuókDoh$å\*ö%Ю=£«…aȼ½÷Û.-½VŒŠ¼'lyî±1¬3ó#ÞE¿ÔS¤gV£m›<HqÚ,sVºóÆß¼Hïô…¹…Méi‡Ò" µùEîØÏj|ÓøVOuœ"f’aÞÞëx…˜ÌO`dHHš×4K*H$‡5×
ÚÄ
Â×CUÅAŠŒsr»2°ÄÁiÚ±Çéõe•¶_SÕÆÃ3ˆ•-3´‘¸¡‡cgDîÚ¦ÃcX}'êûJè½9ñìÓ­ä±	×ÓûçÁmO”üVÞ¸÷¥ I~“ÒôhhûýÑwxlïZ¹G¡4ž=”)º£ò
®vÆŽ%UqÝ4qž©­hûÎí‡š§é1R±cÜèðà y' °ôy¦£q§Ýï¬;šÖõ„Sÿ ›  z('S†$Ï}*evÚ¾Kýº8ý
¨å	jÛ]´-‚6«¶ÖK+8ÊiS45jrœèËQDüDØ]R”˜SPÃ
xJÕl>
=§\û"—WU¤ÚǼÿ ÂnÁ
GŒÃ
‚õN	D³õNÚíŒÕ;HôyÄÈ©P¹Ä{:?R‘Ô¨âF÷ø£bÅó® JS|‚R÷ivýáâ€Æé¡è³´IئÑT!§˜•Øª‚¬â@q€wnïCWÄ@JU€ê¯m6]Ï:£âx
'+ÒðXvÓ¦Úm=–´7œ $ì“B£~p%ÕŸUþ« N@¼üï~w˜ñø5®—'Ôe»¤5ã//€ž~‰Tþ›Å7•#¤×Íö
pÄ$ùeåì*«ÓŠEØWEÈsßg¦ûvžSsLpºÊW–âµEWöˬH;™!CYõZÃÄf æ#1W.
\uWâ\,\Çfj’<qTbên›Î[vxx£ë 'ö¨1›˜ÀM¼Pÿ H)ƒêêŒA7s,|F“꺸k³9Ìö*ç®;Ö!Ö$Eiž•¹ÒÚ†ýóéÝû¾ÕS®ó$’NÝäŸz¤5r¦ãÄÃD÷Üø!°ø‡Ô&@m™Ì^Ãä­d	q5Lnÿ N;.6½·N|#ä"1Nƒx“ã<3('&ñß
t  ~ªu”1Tb㫨9ê–›–bìd$ߣ=#ÕãÒmU¯eí$EFù5ýYô櫨æ왍Ǘ±ssM]·á¿
0ÕåJRÓªîiƒ+O58ÖñªŠÒx"	\µâá¨i’¤i
—Ö
”
M+M¤ë9‚‰A¦°Qõ¾ßøK~¼Ã‘g…Ö´~÷Ï[3GUœÒ½#…kàÔ®Ò”‰³·dWV‰IP‰Ú8u¹”E
ÖqLj¾êÕCBš{A^Âß;–¨`¯¬ìö
˼	×tìø.tƐm*n¨y4o&Àx¥n¦×î‡aupáÛj8¿m›è¶ã!o½;ß0y^ý×^EÑ¿ÒjzŒ­)vÚÑnÄL
…^ªô× ‡—‚3k	Îý­hï]içå–îÏ*÷ñþ»Ô
CÒjøjÍznˆ´
¹#b'Fô‹
‰v¥'’à'T´ƒHýÍ%M‰ ƒ&ÆÇŒï1 ‘	–Þ
‰i¬s žR-Ÿ kŠ¬á¬7:þ 0ŒÅÒÕ/aÙ¬ÃÝ#Úøœ
©aiVc‰. ¹¦ãµ”
›Yg¦›ÆÎýº°f³7ƒhá·¸­}&D9¡ÂsÉÙÞèŠõØàC™¨ñbFC|´Ü(ŸƒÚÒ-%»'a	Ì¿)ËÇn¿úÿ ÞŽX…4ÊÅH^ôΑí@ù¹Eh¶“L8Çjù
¼ÎåVªóR©Ï5uÃ
V4lZß®=€xÖŸ–ÑÈ
÷”¨°¾__yM1tÉ?uÆþIkÄgæ@þ[¢†°XÃJ£j·:nkÅ¢u‘}âGzö­/IµèŠ¬¼48q¦F°ŽR¼=ûì{´¯RýicS
ÕÛ íNtÍÙï£,w4rêì®»~x(©Uñ§#Ñ&œÕ¤>ÎåÍÓ9’Ö{9eV­[Öjâ²ãu]˜å2›qÑšÕJç0€sÄ|Êëè0튔bÁ>“{×_F`Ø©ºê:µä,v¤ðfc1±"«ÔÍän1#=·
Âøv~H<Q-Ìk7Æ;•L´©ÙC°.7
¯hKL@ävÊâž$´4¸ð‚¦­R–ÂZ7ÕÃj±·¿rÓrªJ_PÕ.#g¤gÀ)©`ª<KžèÝ'ä©èÒ3rwû€Ø¦ÒƒLf¤
,¿I½{Ƕ8‘$KÝU/Oi>½ÐßA¾¿Ü€Óš]Õ; I¾÷ç‚Qi†î¹9ywÔKG˜áñ zQY—§ÃÕZ07§X‚Áh;ÁM)iÌCH-¯T‘ë|A0{Ò½LÚ–TâÖkÜ’dÀ“rmm»”جPF³ÖcbE§T€ÒxKºû’Ó®7±²(\4ŽÃ¸Uu@j™yĵ;³µ!Á¢b.W¤=mõ´êµKk
¸K^ÜÛ#p*Ü14qkZç5ïë†°5Ï%ÍÛ<Õ¤×Ô¥ê†C	Õ´¼ú$ƒÖ“”]Ù¬qÞÚ[4©ý!ûÏ—Áb쳐XµA¬â~`›Çr¸8ìùÝ䫦<>ä÷«?xs´ÇÑ	/á;¹øüÊÈÙà{"@Žïzâ¬[âß‚ U_<ÇŸ½4èN˜ú61®qŠu ¦þF£»äJ_ˆÙÎ~ ÞAã–Ý„Ï—rŠD;xTž‘ô`É«…suãO`?³à™ô
Lý#Íc5öoæØ‚y´´÷«ZR§<&JÇ+éâô´€i!Àˆ0æAoàðLèÖ-2ŸõW.’t^–(KÁmHµV@xÜÇy®Ñø­â^:Ú3w· 7½¹°ñ¸â¹®:',«Mœ—n­Á+Ãbš
LÈ‘ÄnRÓÅœ%¦²‰¨ùQ:¤f‚ "PÕtô¸…cæl…&˜Ú˜Ôkv‹ž+vŠ,=¢v­6—X
y*¥t£«<™:“aï<QÝ&Ó]i4音äzçáíHÚÕxcòãæäÝÔm퐡 `Â)C×ehÀdHP6ÅMEöZ®Í¨	é¾Tr뢘6*¶;´sÙì]ÊŽŽÛíÉwRÈ´up* Ã	‚m´:Û{·”MUë©õ̤êÔo7:ŽÕ
qÏ'E ˆk^uãT€$Ú$Æ{•ŸBP°al¾Ž©ŒÃ^}äA
,º­$Ü]ºÚ.í:‹¤ÜöXnno7X€¥BÂà ±1ã>Œºîϲ=¦6rO]XI¿Œ÷¤zÚ­›¶ 6÷”w\dü~v®ˆÌk«^m<ÿ ¢‰Õ\)ùºŽ;… lîÙÅEŠ®cѾ@vnMÏ,¼“
ñ•ŽBxðÃzãÇç%3ˆ"}Ù•Åî>
BÉú;Ò]V+P˜F_´ßé>
Øše|ï‡ÄOmFæÇ ãqÞ$/xÐx­z`ï9"œÜij‚!7.\Td…9M‡•iŽ‹¾‘50ÞŽn¥ß4ÉôO¹*í^QêËÜÇÌ8=Ž
§s‰'ÂëÙ«á%Pú[O
†ÅP¯VsŽ°.‰,kc¶ ¬A9n˜XÎ-ÞšN["¹QÕ‰ƒMýÁߺXJæÍaLj¾×Ãmã¾ãÚ uñÒþåQô¦¥
/ÄUx:‚ÍÜ’ Đ©ØÝ3V¨‰ÕnÐ6ó*óúK­«…c ¯U òhsý­jóÔj#,ímŒRµ«lbïUTŒÑ8†Ä0œÏr`ð¡¬É	Ї
ë"À²

™	6¥ f¶¢ÚoܱԷ-<Àî)†a¶ž'Ú»¨TXqØæ¶÷Y
ÄHy˜9ÈIW­YÀuMFë
ºÏ’AqÌ4·/Ú
†ô'i$øä­=Ä
Ý|öK×40è|È6p‘0§)o¥ctî§H+CA-“ xØ|ÐXŠç
l8íºð3Ø:³¤¬KX¯UÿÙ
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
<HTML>
<HEAD>
 <META NAME="GENERATOR" CONTENT="LinuxDoc-Tools 0.9.72">
 <TITLE>Linux 2.4 NAT HOWTO: Controlling What To NAT</TITLE>
 <LINK HREF="NAT-HOWTO-6.html" REL=next>
 <LINK HREF="NAT-HOWTO-4.html" REL=previous>
 <LINK HREF="NAT-HOWTO.html#toc5" REL=contents>
</HEAD>
<BODY>
<A HREF="NAT-HOWTO-6.html">Next</A>
<A HREF="NAT-HOWTO-4.html">Previous</A>
<A HREF="NAT-HOWTO.html#toc5">Contents</A>
<HR>
<H2><A NAME="s5">5.</A> <A HREF="NAT-HOWTO.html#toc5">Controlling What To NAT</A></H2>

<P>You need to create NAT rules which tell the kernel what connections
to change, and how to change them.  To do this, we use the very
versatile <CODE>iptables</CODE> tool, and tell it to alter the NAT table by
specifying the `-t nat' option.</P>

<P>The table of NAT rules contains three lists called `chains': each
rule is examined in order until one matches.  The two chains are
called PREROUTING (for Destination NAT, as packets first come in), and
POSTROUTING (for Source NAT, as packets leave).  The third (OUTPUT)
will be ignored here.</P>

<P>The following diagram would illustrate it quite well if I had any
artistic talent:</P>
<P>
<BLOCKQUOTE><CODE>
<PRE>
      _____                                     _____
     /     \                                   /     \
   PREROUTING -->[Routing ]----------------->POSTROUTING----->
     \D-NAT/     [Decision]                    \S-NAT/
                     |                            ^
                     |                            |
                     |                            |
                     |                            |
                     |                            |
                     |                            |
                     |                            |
                     --------> Local Process ------
</PRE>
</CODE></BLOCKQUOTE>
</P>
<P>At each of the points above, when a packet passes we look up what
connection it is associated with.  If it's a new connection, we look
up the corresponding chain in the NAT table to see what to do with it.
The answer it gives will apply to all future packets on that
connection.</P>

<H2><A NAME="ss5.1">5.1</A> <A HREF="NAT-HOWTO.html#toc5.1">Simple Selection using iptables</A>
</H2>

<P><CODE>iptables</CODE> takes a number of standard options as listed
below.  All the double-dash options can be abbreviated, as long as
<CODE>iptables</CODE> can still tell them apart from the other possible
options.  If your kernel has iptables support as a module, you'll need
to load the ip_tables.o module first: `insmod ip_tables'.</P>

<P>The most important option here is the table selection option, `-t'.
For all NAT operations, you will want to use `-t nat' for the NAT
table.  The second most important option to use is `-A' to append a
new rule at the end of the chain (e.g. `-A POSTROUTING'), or `-I' to
insert one at the beginning (e.g. `-I PREROUTING').</P>

<P>You can specify the source (`-s' or `--source') and destination
(`-d' or `--destination') of the packets you want to NAT.  These
options can be followed by a single IP address (e.g. 192.168.1.1), a
name (e.g. www.gnumonks.org), or a network address
(e.g. 192.168.1.0/24 or 192.168.1.0/255.255.255.0).</P>

<P>You can specify the incoming (`-i' or `--in-interface') or outgoing
(`-o' or `--out-interface') interface to match, but which you can
specify depends on which chain you are putting the rule into: at
PREROUTING you can only select incoming interface, and at POSTROUTING
you can only select outgoing interface.  If you use the
wrong one, <CODE>iptables</CODE> will give an error.</P>

<H2><A NAME="ss5.2">5.2</A> <A HREF="NAT-HOWTO.html#toc5.2">Finer Points Of Selecting What Packets To Mangle</A>
</H2>

<P>I said above that you can specify a source and destination address.
If you omit the source address option, then any source address will
do.  If you omit the destination address option, then any destination
address will do.</P>

<P>You can also indicate a specific protocol (`-p' or `--protocol'),
such as TCP or UDP; only packets of this protocol will match the rule.
The main reason for doing this is that specifying a protocol of tcp or
udp then allows extra options: specifically the `--source-port' and
`--destination-port' options (abbreviated as `--sport' and `--dport').</P>

<P>These options allow you to specify that only packets with a certain
source and destination port will match the rule.  This is useful for
redirecting web requests (TCP port 80 or 8080) and leaving other
packets alone.</P>

<P>These options must follow the `-p' option (which has a side-effect
of loading the shared library extension for that protocol).  You can
use port numbers, or a name from the /etc/services file.</P>

<P>All the different qualities you can select a packet by are detailed
in painful detail in the manual page (<CODE>man iptables</CODE>).</P>

<HR>
<A HREF="NAT-HOWTO-6.html">Next</A>
<A HREF="NAT-HOWTO-4.html">Previous</A>
<A HREF="NAT-HOWTO.html#toc5">Contents</A>
</BODY>
</HTML>