▁also ▁known ▁as ▁edge ▁L SR ) ▁is ▁a ▁router ▁that ▁oper ates ▁at ▁the ▁edge ▁of ▁an ▁M PL S ▁network ▁and ▁acts ▁as ▁the ▁entry ▁and ▁exit ▁points ▁for ▁the ▁network . ▁L ER s ▁push ▁an ▁M PL S ▁label ▁onto ▁an ▁incoming ▁packet ▁and ▁pop ▁it ▁off ▁an ▁out going ▁packet . ▁Alternatively , ▁under ▁pen ult imate ▁hop ▁po pping ▁this ▁function ▁may ▁instead ▁be ▁performed ▁by ▁the ▁L SR ▁directly ▁connected ▁to ▁the ▁L ER . ▁ ▁When ▁forward ing ▁an ▁IP ▁dat agram ▁into ▁the ▁M PL S ▁domain , ▁a ▁L ER ▁uses ▁routing ▁information ▁to ▁determine ▁the ▁appropriate ▁label ▁to ▁be ▁aff ixed , ▁labels ▁the ▁packet ▁accordingly , ▁and ▁then ▁for wards ▁the ▁l abeled ▁packet ▁into ▁the ▁M PL S ▁domain . ▁Like wise , ▁upon ▁receiving ▁a ▁l abeled ▁packet ▁which ▁is ▁dest ined ▁to ▁exit ▁the ▁M PL S ▁domain , ▁the ▁L ER ▁stri ps ▁off ▁the ▁label ▁and ▁for wards ▁the ▁resulting ▁IP ▁packet ▁using ▁normal ▁IP ▁forward ing ▁rules . ▁ ▁Pro vider ▁router ▁In ▁the ▁specific ▁context ▁of ▁an ▁M PL S - based ▁virtual ▁private ▁network ▁( V PN ), ▁L ER s ▁that ▁function ▁as ▁ing ress ▁and / or ▁e gress ▁rou ters ▁to ▁the ▁V PN ▁are ▁often ▁called ▁P E ▁( Provider ▁Edge ) ▁rou ters . ▁Dev ices ▁that ▁function ▁only ▁as ▁trans it ▁rou ters ▁are ▁similarly ▁called ▁P ▁( Provider ) ▁rou ters . ▁The ▁job ▁of ▁a