In my opinion, FIB doesn't have MPLS label, FIB should be populate from RIB because of CEF. However, after I seach online and find out that some tutorial stated that FIB also contains the label just like LFIB. enter image description here

enter image description here

However, I cannot find any label or image that contains MPLS with the command "show ip cef"

2 Answers 2


There is no formally specified/accepted definition of "FIB" -- as far as I'm aware the first use was at Cisco back in the late 90's when the new architecture "Cisco Express Forwarding" (CEF) was implemented.

While I'd argue that it is MOST common to hear people use the term "FIB" to mean "the set of lookup tables and databases that we use to do IPv4/IPv6 lookups, resolve forwarding adjacencies, do loadbalancing, etc." -- it's also quite common to have people talk about "the FIB" as a larger container for all things forwarding-related within the router.

You'll sometimes hear people say "LFIB" (label-FIB) or even sometimes MPLS-FIB, when they are referring specifically to the forwarding state based on MPLS label values rather than IP addresses.

Additionally, when you're doing MPLS label imposition based on an IP lookup, you have to store the label(s) that you're adding to the packet somewhere, and most people would call that "part of the FIB". When you do various flavors of show ip cef you will sometimes see these label values included there. Where exactly those values are stored in the router's forwarding hardware is totally platform dependent. Sometimes it's a purely software router so everything lives in main memory, some times it's a very high speed hardware based system where the different parts of the forwarding chain are broken up into separate physical memories for performance reasons.

But I think the actual answer is that it's not strictly defined, and you sort of have to have some context to be able to know exactly what it means in a given settings.

Source: self, cisco employee and breaker of FIB implementations since 1997...


enter image description here

From show ip cef,we can see that FIB do have MPLS label

  • 1
    Please don't paste screenshots, paste the actual text instead.
    – Teun Vink
    Commented Jul 18, 2023 at 8:47

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