Hi all, i have a very basic question regarding mpls labels. i have read in various books and seen it practically that for directly connected links a router will advertise the prefix with imp null label which is shown as POP tag on the neighoring router. My question is why is this so ?? consider the following scenario
I have enabled mpls ip on links between R1, R2 and R3. When R1 advertises the link between R4 and itself (lets say its 184.108.40.206/8) then on R2 i see it as POP tag ok ?? why is R1 advertising it as a imp null label ? since mpls is not enabled on it why bother assigning it any label at all ?? i am aware of PHP but this what confuses me, since 220.127.116.11/8 is a pure ip network then why R1 doesnt assign any label at all and on R2 shall i see UNTAGGED !! i mean why this is not the behaviour !!
Can some1 guide me in this pls ??? pls tell me why R1 is using PHP for a pure ip network ?