ÿØÿà JFIF ÿÛ „ ( %"1!%)+...383,7(-.+
-+++--++++---+-+-----+---------------+---+-++7-----ÿÀ ß â" ÿÄ ÿÄ H !1AQaq"‘¡2B±ÁÑð#R“Ò Tbr‚²á3csƒ’ÂñDS¢³$CÿÄ ÿÄ % !1AQa"23‘ÿÚ ? ôÿ ¨pŸªáÿ —åYõõ\?àÒü©ŠÄï¨pŸªáÿ —åYõõ\?àÓü©ŠÄá 0Ÿªáÿ Ÿå[úƒ ú®ði~TÁbqÐ8OÕpÿ ƒOò¤Oè`–RÂáœá™êi€ßÉ< FtŸI“öÌ8úDf´°å}“¾œ6
öFá°y¥jñÇh†ˆ¢ã/ÃÐ:ªcÈ
"Y¡ðÑl>ÿ ”ÏËte:qž\oäŠe÷ó²·˜HT4&ÿ ÓÐü6ö®¿øþßèô Ÿ•7Ñi’•j|“ñì>b…þS?*Óôÿ ÓÐü*h¥£ír¶ü UãS炟[AÐaè[ûª•õ&õj?†Éö+EzP—WeÒírJFt ‘BŒ†Ï‡%#tE Øz ¥OÛ«!1›üä±Í™%ºÍãö]°î(–:@<‹ŒÊö×òÆt¦ãº+‡¦%Ìòh´OƒJŒtMÜ>ÀÜÊw3Y´•牋4ÇýÊTì>œú=Íwhyë,¾Ôò×õ¿ßÊa»«þˆÑªQ|%6ž™A õ%:øj<>É—ÿ Å_ˆCbõ¥š±ý¯Ýƒï…¶|RëócÍf溪“t.СøTÿ *Ä¿-{†çàczůŽ_–^XþŒ±miB[X±d 1,é”zEù»&
î9gœf™9Ð'.;—™i}!ôšåîqêÛ٤ёý£½ÆA–àôe"A$ËÚsäÿ
÷Û #°xŸëí(l
»ý3—¥5m!
rt`†0~'j2(]S¦¦kv,ÚÇl¦øJA£Šƒ
J3E8ÙiŽ:cÉžúeZ°€¯\®kÖ(79«Ž:¯X”¾³Š&¡* ….‰Ž(ÜíŸ2¥ª‡×Hi²TF¤ò[¨íÈRëÉä¢mgÑ.Ÿ<öäS0í„ǹÁU´f#Vß;Õ–…P@3ío<ä-±»Ž.L|kªÀê›fÂ6@»eu‚|ÓaÞÆŸ…¨ááå>åŠ?cKü6ùTÍÆ”†sĤÚ;H2RÚ†õ\Ö·Ÿn'¾ ñ#ºI¤Å´%çÁ‚â7›‹qT3Iï¨ÖÚ5I7Ë!ÅOóŸ¶øÝñØôת¦$Tcö‘[«Ö³šÒ';Aþ ¸èíg
A2Z"i¸vdÄ÷.iõ®§)¿]¤À†–‡É&ä{V¶iŽ”.Ó×Õÿ û?h¬Mt–íª[ÿ Ñÿ ÌV(í}=ibÔ¡›¥¢±b Lô¥‡piη_Z<‡z§èŒ)iÖwiÇ 2hÙ3·=’d÷8éŽ1¦¸c¤µ€7›7Ø ð\á)} ¹fËí›pAÃL%âc2 í§æQz¿;T8sæ°qø)QFMð‰XŒÂ±N¢aF¨…8¯!U Z©RÊ ÖPVÄÀÍin™Ì-GˆªÅËŠ›•zË}º±ŽÍFò¹}Uw×#ä5B¤{î}Ð<ÙD
é©¤&‡ïDbàÁôMÁ."
¤‡ú*õ'VŽ|¼´Úgllº¼klz[Æüï÷Aób‡Eÿ dÑ»Xx9ÃÜ£ÁT/`¼¸vI±Ýµ·Ë‚“G³þ*Ÿû´r|*}<¨îºœ @¦mÄ’M¹”.œ«Y–|6ÏU¤jç¥ÕÞqO
˜kDÆÁ¨5ÿ š;Њ¦¦€GÙk \
–Þ=â¼=SͧµªS°ÚÍpÜãQűÀõ¬?ÃÁ1Ñ•õZà?hóœ€
L¦l{Y*K˜Ù›zc˜–ˆâø+¾ -Ök¥%ùEÜA'}ˆ><ÊIè“bpÍ/qÞâvoX€w,\úªò6Z[XdÒæ@Ö—€$òJí#é>'°Ú
ôª˜<)4ryÙ£|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+DÙrmÎ…_ªæ»ŠÓœ¡¯’Ré9MÅ×D™lælffc+ŒÑ,ý™ÿ ¯þǤ=Å’Á7µ÷ÚÛ/“Ü€ñýã¼àí¾ÕÑ+ƒ,uµMâÀÄbm:ÒÎPæ{˜Gz[ƒ¯«® KHà`ߨŠéí¯P8Aq.C‰ à€kòpj´kN¶qô€…Õ,ÜNŠª-{Zö’æû44‰sŽè‰îVíRœÕm"
6?³D9¡ÇTíÅꋇ`4«¸ÝÁô ï’ýorqКÇZ«x4Žâéþuïf¹µö[P ,Q£éaX±`PÉÍZ ¸äYúgüAx
’6Lê‚xÝÓ*äQ
Ï’¨hÍ
=²,6ï#rÃ<¯–£»ƒ‹,–ê•€ aÛsñ'%Æ"®ÛüìBá HÚ3ß°©$“XnœÖ’î2ËTeûìxîß
¦å¿çÉ
ðK§þ{‘t‚Ϋ¬jéîZ[”š7L¥4VÚCE×]m¤Øy”ä4-dz£œ§¸x.*ãÊÊ b÷•h:©‡¦s`BTÁRû¾g⻩‹jø sF¢àJøFl‘È•Xá“à~*j¯ +(ÚÕ6-£¯÷GŠØy‚<Ç’.F‹Hœw(+)ÜÜâÈzÄäT§FߘãÏ;DmVœ3Àu@mÚüXÝü•3B¨òÌÁÛ<·ÃÜz,Ì@õÅ·d2]ü8s÷IôÞ¯^Ç9¢u„~ëAŸï4«M?
K]ÅàPl@s_ p:°¬ZR”´›JC[CS.h‹ƒïËœ«Æ]–÷ó‚wR×k7X‰k›‘´ù¦=¡«‰¨¨Â')—71ó’c‡Ðúµ
`é.{§p¹ój\Ž{1h{o±Ý=áUÊïGÖŒõ–-BÄm+AZX¶¡
ïHðæ¥JmÙ;…䡟ˆ¦ ° äšiÉg«$üMk5¤L“’çÊvïâï ,=f“"íἊ5ô¬x6{ÉžID0e¸vçmi'︧ºð9$ò¹÷*£’9ÿ ²TÔ…×>JV¥}Œ}$p[bÔ®*[jzS*8
”·T›Í–ñUîƒwo$áè=LT™ç—~ô·¤ÈÚ$æ¦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®qZcqJêäÞ-ö[ܘbň±çb“ж31²n×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‘%"©<Ôúʰsº UZvä‡ÄiÆÒM .÷V·™ø#kèýií The kernel starts with three lists of rules in the `filter' table;
these lists are called firewall chains or just
chains. The three chains are called INPUT,
OUTPUT and FORWARD. For ASCII-art fans, the chains are arranged like so: (Note: this
is a very different arrangement from the 2.0 and 2.2 kernels!)
Œºîϲ=¦6rO]XI¿Œ÷¤zÚ›¶ 6÷”w\dü~v®ˆÌk«^m<ÿ ¢‰Õ\)ùºŽ;… lîÙÅEŠ®cѾ@vnMÏ,¼“ñ•ŽBxðÃzãÇç%3ˆ"}Ù•Åî>
BÉú;Ò]V+P˜F_´ßé>
Øše|ï‡ÄOmFæÇ ãqÞ$/xÐxz`ï9"œÜij‚!7.\Td…9M‡•iŽ‹¾‘50ÞŽn¥ß4ÉôO¹*í^QêËÜÇÌ8=ާs‰'ÂëÙ«á%Pú[O
†ÅP¯Vsް.‰,kc¶ ¬A9n˜XÎ-ÞšN["¹QÕ‰ƒMýÁߺXJæÍaLj¾×Ãmã¾ãÚ uñÒþåQô¦¥
/ÄUx:‚ÍÜ’ Ä©ØÝ3V¨‰ÕnÐ6ó*óúK«…c ¯U òhsýjóÔj#,ímŒRµ«lbïUTŒÑ8†Ä0œÏr`ð¡¬É Ї
ë"À²
™ 6¥ f¶¢ÚoܱԷ-<Àî)†a¶ž'Ú»¨TXqØæ¶÷YÄHy˜9ÈIWYÀuMFë
ºÏ’AqÌ4·/Ú
†ô'i$øä=Ä
Ý|öK×40è|È6p‘0§)o¥ctî§H+CA-“ xØ|ÐXŠç
l8íºð3Ø:³¤¬KX¯UÿÙ
6. How Packets Traverse The Filters
_____
Incoming / \ Outgoing
-->[Routing ]--->|FORWARD|------->
[Decision] \_____/ ^
| |
v ____
___ / \
/ \ |OUTPUT|
|INPUT| \____/
\___/ ^
| |
----> Local Process ----
The three circles represent the three chains mentioned above. When a packet reaches a circle in the diagram, that chain is examined to decide the fate of the packet. If the chain says to DROP the packet, it is killed there, but if the chain says to ACCEPT the packet, it continues traversing the diagram.
A chain is a checklist of rules. Each rule says `if the packet header looks like this, then here's what to do with the packet'. If the rule doesn't match the packet, then the next rule in the chain is consulted. Finally, if there are no more rules to consult, then the kernel looks at the chain policy to decide what to do. In a security-conscious system, this policy usually tells the kernel to DROP the packet.