Refer to the exhibit. What does the imp-null tag represent in the MPLS VPN cloud?
Refer to the exhibit. What does the imp-null tag represent in the MPLS VPN cloud?
The imp-null (implicit null) tag instructs the upstream router to pop the tag entry off the tag stack before forwarding the packet. This process is commonly known as Penultimate Hop Popping (PHP), where the router just before the last router removes the label to simplify the forwarding process for the final destination router. This makes option 'Pop the label' the correct answer.
Just for reference: Label-Switched Path (LSP) - The path that a labeled packet traverses through a network, from label imposition to disposition. P/PE and C/CE - P and PE routers are LSRs and LERs in the context of MPLS-VPN. The term P comes from routers being in the provider network. C routers are routers found in the customer network. CE routers are the routers on the customer edge facing the provider. PE routers are provider edge routers, which connect to the CE routers. CE routers normally run plain IP (not required to be MPLS-aware). Ref: https://www.ccexpert.us/traffic-engineering/mpls-terminology.html
This looks more like a comment to Q57 :-)
PHP (Penultimate Hop Popping) When exchanging labels, the LER informs the LSR of Implicit Null with a label value of 3. When forwarding Implicit Null (imp-null) to the other party, LSR removes the label and forwards it.
Answer A Explanation: The imp-null (implicit null) tag instructs the upstream router to pop the tag entry off the tag stack before forwarding the packet. Note: pop means remove the top MPLS labe
The given answer is correct. TDP (the Tag Distribution Protocol) https://www.cisco.com/c/en/us/support/docs/multiprotocol-label-switching-mpls/mpls/12492-mpls-tsh.html https://www.ipspace.net/kb/tag/MPLS/Implicit_Explicit_NULL.html
The given answer is correct - Pop the label
A is correct