▁the ▁po pped ▁label ▁was ▁the ▁last ▁on ▁the ▁label ▁stack , ▁the ▁packet ▁" le aves " ▁the ▁M PL S ▁tunnel . ▁This ▁can ▁be ▁done ▁by ▁the ▁e gress ▁router , ▁but ▁see ▁Pen ult imate ▁Hop ▁Po pping ▁( PHP ) ▁below . ▁ ▁During ▁these ▁operations , ▁the ▁contents ▁of ▁the ▁packet ▁below ▁the ▁M PL S ▁Label ▁stack ▁are ▁not ▁exam ined . ▁Indeed , ▁trans it ▁rou ters ▁typically ▁need ▁only ▁to ▁examine ▁the ▁top most ▁label ▁on ▁the ▁stack . ▁The ▁forward ing ▁of ▁the ▁packet ▁is ▁done ▁based ▁on ▁the ▁contents ▁of ▁the ▁labels , ▁which ▁allows ▁" protocol - in dependent ▁packet ▁forward ing " ▁that ▁does ▁not ▁need ▁to ▁look ▁at ▁a ▁protocol - dependent ▁routing ▁table ▁and ▁avoid s ▁the ▁expensive ▁IP ▁longest ▁prefix ▁match ▁at ▁each ▁hop . ▁ ▁At ▁the ▁e gress ▁router , ▁when ▁the ▁last ▁label ▁has ▁been ▁po pped , ▁only ▁the ▁payload ▁remains . ▁This ▁can ▁be ▁an ▁IP ▁packet ▁or ▁any ▁of ▁a ▁number ▁of ▁other ▁kinds ▁of ▁payload ▁packet . ▁The ▁e gress ▁router ▁must , ▁therefore , ▁have ▁routing ▁information ▁for ▁the ▁packet ' s ▁payload ▁since ▁it ▁must ▁forward ▁it ▁without ▁the ▁help ▁of ▁label ▁lookup ▁tables . ▁An ▁M PL S ▁trans it ▁router ▁has ▁no ▁such ▁requirement . ▁ ▁Usually ▁( by ▁default ▁with ▁only ▁one ▁label ▁in ▁the ▁stack , ▁accordingly ▁to ▁the ▁M PL S ▁specification ), ▁the ▁last ▁label ▁is ▁po pped ▁off ▁at ▁the ▁pen