Overview

RouterOS routing information consists of two main parts:

• FIB (Forwarding Information Base), that is used to make packet forwarding decisions. It contains a copy of the necessary routing information.
• RIB (Routing Information Base) contains all learned prefixes from routing protocols (connected, static, BGP, RIP, OSPF).

Routing Information Base

Routing Information Base is a database that lists entries for particular network destinations and their gateways (address of the next device along the path or simply nexthop). One such entry in routing table is called route.

By default all routes are organized in one "main" routing table. It is possible to make more than one routing table which we will discuss further in this article, but for now for sake of simplicity we will consider that there is only one "main" routing table

RIB routing table contains complete routing information, including static routes and policy routing rules configured by the user, routing information learned from dynamic routing protocols (RIP, OSPF, BGP) and information about connected networks.

Its purpose is not just to store routes, but also to filter routing information, to calculate best route for each destination prefix, to build and update Forwarding Information Base and to distribute routes between different routing protocols.

Connected Routes

Connected routes are created automatically for each IP network that has at least one enabled interface attached to it (as specified in the /ip address or /ipv6 address configuration). RIB tracks status of connected routes, but does not modify them. For each connected route there is one IP address item such that:

• address part of dst-address of connected route is equal to network of IP address item.
• netmask part of dst-address of connected route is equal to netmask part of address of ip address item.
• interface of connected route is equal to actual-interface of IP address item (same as interface, except for bridge interface ports).