5

Forwarding Information Base (FIB) also called Forwarding Table or Mac Table according to wikipedia.

I first explain my understanding of the FIB in both Switch and Router. Does not hesitate to correct myself, I'm here to learn and clarify my doubts.

In a Switch (layer 2), the Mac adresse of devices in the local network is associate with the egress interface. This data in stock in the FIB and the Switch use to forward packet. Here I understand why we call this "Mac Table".

MAC-A | Interface 1

MAC-B | Interface 2

...

The MAC destination is learned by the switch with ARP or Flooding.

The FIB in a router perform the Data Plane, contrary to the RIB which perform Control Plane. Indeed the FIB contain the best route selected from the RIB. When a packet come to the router, it use the FIB to select the route and it use the next-hop. It replace the Destination Mac Address with the Mac Address of the next-hop.

So, the FIB in switch and router are two different concept ? The FIB of a router does not contain Mac Adress, so why this is also called Mac table ?

I hope I was clear.

6

Calling a switch mac address table a Forwarding Information Base is incorrect. The correct term, according to the original 8021.D document is Filtering Database, although this term is not commonly used. This database is more often referred as a Mac Address Table -not to be confused with the ARP table- this is the term you will find in many switch interface or command line interface commands.

So:

  • at layer 2 for Ethernet switches operations you have a Filtering Database, also known as "Mac Address Table", which contains MAC addresses, learned by the switch when it receives a frame
  • at layer 3 for IP routers you have one or several Routing Information Base (RIB), built automatically (connected networks), manually (static routes) or by routing protocols (BGP, OSPF, EIGRP, IS-IS, RIP...) and a Forwarding Information Base(FIB), which is the base built by picking the best route for each network in the various RIBs. The router uses the FIB to determine the destination of a given packet.

Wikipedia is not always right (nor Juniper as they do the mistake in this page, which may be the source of the error in Wikipedia)...

  • I thinked that was similar in router and switch. Thanks you, this seems more logical to me now. – Eraseth Mar 3 '18 at 16:14

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