Which table is used to map the packets in an MPLS LSP that exit from the same interface, via the same next hop, and have the same queuing policies?
Which table is used to map the packets in an MPLS LSP that exit from the same interface, via the same next hop, and have the same queuing policies?
The correct answer is CEF. In MPLS, the router's FIB (Forwarding Information Base), maintained by CEF (Cisco Express Forwarding), is used to determine the routing of packets. The CEF table is used to build the LFIB (Label Forwarding Information Base), which contains the mapping of packets to their MPLS labels. Thus, the CEF table is the one used for mapping packets that exit through the same interface, have the same next hop, and follow the same queuing policies.
FOR ME IS "B", Because, I think there is a problem in the question, the word "table", the rest of the question is the same FEC concept, the same label for several pefixes with the same next hop and the same queuing policies.
A forwarding equivalence class (FEC) is a term used in Multiprotocol Label Switching (MPLS) to describe a set of packets with similar or identical characteristics which may be forwarded the same way; that is, they may be bound to the same MPLS label.
Given Answer is correct, for references see: https://learningnetwork.cisco.com/s/question/0D53i00000Ksx8ZCAR/what-is-fec-in-mpls-and-how-it-works-
CEF isnt a table either. My guess is FEC.
For me it's CEF, because this table is used for creating the LSP. Plus, FEC is not a table, it is rather an attribute (e.g. a destination IP subnet is a typical FEC).
I agree the LFIB is based on FIB, again in my opinion this question is just "wrong". It is written in very bad Cisco english. Just pick B or C, in a way they can be both wrong or right. Personally i think they are hinting at "FEC" but again, i understand your reasoning as it is NOT a table.
B is correct FEC (Forwarding Equivalence Class) is a key concept in MPLS. It groups packets that are forwarded in the same manner, which means they exit through the same interface, follow the same next hop, and have the same queuing policies.
B is the Answer
According to the link HungarianDish provided, it seems they are asking for CEF as it is an actual "table" use to populate FEC attributes.
https://community.cisco.com/t5/routing/why-cef-needed-in-mpls-network/td-p/1699091 cisco MPLS code ...uses as input data the FIB (Forwarding Information Base) mantained by CEF, to build the LFIB that is the table where for each FEC there is an association with a label taken from the local node label space. ...the biggest difference is that the CEF table is kept local and not exported to any other device. MPLS FEC/label bindings are advertised.
https://www.networkworld.com/article/2291724/chapter-7--understanding-cef-in-an-mpls-vpn-environment.html MPLS creates its own database for lookups called the Label Forwarding Information Base (LFIB), but it uses the CEF FIB as a source of this information. In the direction of label imposition, the router switches packets based on a CEF table lookup to find the next hop and adds the appropriate label information stored in the FIB for the destination.
The question describes FEC, however, the table which being used is Label Forwarding Information Base (LFIB) in Cisco terms or "FEC-to-NHLFE" (FTN) table according to RFC 3031. LFIB is using CEF table + LIB. As well as I see, none of the answers are correct.
Good explanations: https://community.cisco.com/t5/routing/mpls-tables/td-p/2305490 https://www.ccexpert.us/routing-switching/mpls-packet-forwarding-and-label-switched-paths.html
RFC 3031 https://datatracker.ietf.org/doc/rfc3031/