OUT ING : ▁Pack ets ▁will ▁enter ▁this ▁chain ▁before ▁a ▁routing ▁decision ▁is ▁made . ▁ ▁IN PUT : ▁Pack et ▁is ▁going ▁to ▁be ▁locally ▁delivered . ▁It ▁does ▁not ▁have ▁anything ▁to ▁do ▁with ▁processes ▁having ▁an ▁opened ▁socket ; ▁local ▁delivery ▁is ▁controlled ▁by ▁the ▁" local - d elivery " ▁routing ▁table : ▁ip ▁route ▁show ▁table ▁local . ▁ ▁FOR W ARD : ▁All ▁packets ▁that ▁have ▁been ▁rout ed ▁and ▁were ▁not ▁for ▁local ▁delivery ▁will ▁traverse ▁this ▁chain . ▁ ▁OUT PUT : ▁Pack ets ▁sent ▁from ▁the ▁machine ▁itself ▁will ▁be ▁visit ing ▁this ▁chain . ▁ ▁POST RO UT ING : ▁Rout ing ▁decision ▁has ▁been ▁made . ▁Pack ets ▁enter ▁this ▁chain ▁just ▁before ▁hand ing ▁them ▁off ▁to ▁the ▁hardware . ▁ ▁A ▁chain ▁does ▁not ▁exist ▁by ▁itself ; ▁it ▁belongs ▁to ▁a ▁table . ▁There ▁are ▁three ▁tables : ▁nat , ▁filter , ▁and ▁m angle . ▁Unless ▁preced ed ▁by ▁the ▁option ▁- t , ▁an ▁i pt ables ▁command ▁concerns ▁the ▁filter ▁table ▁by ▁default . ▁For ▁example , ▁the ▁command ▁i pt ables ▁- L ▁- v ▁- n , ▁which ▁shows ▁some ▁ch ains ▁and ▁their ▁rules , ▁is ▁equivalent ▁to ▁i pt ables ▁- t ▁filter ▁- L ▁- v ▁- n . ▁To ▁show ▁ch ains ▁of ▁table ▁nat , ▁use ▁the ▁command ▁i pt ables ▁- t ▁nat ▁- L ▁- v ▁- n ▁ ▁Each ▁rule ▁in ▁a ▁chain ▁contains ▁the