I need a clarification how the lables are swapped between ASBR's for two different AS's in case of Inter-AS L3 MPLS VPN OptionB.
Because when i see a route from PE-ISP-A for a prefix it has two label stack. One has come from the remote end PE (PE-ISP-B) inner label or VPN label, and the other label is called the IGP label which will be used to reach the ASBR-ISP-A.
So my query is when the packet has come to ASBR-ISP-A, Will the packet go as labels or without any lables to ASBR-ISP-B.
If packet has gone to ASBR-ISP-B without any labels then how ASBR-ISP-B knows the packet has to reach the PE-ISP-B because we dont populate the VRF routing table in ASBR's in case of Option-B.
Thanks in advance.