FORWARDING INFORMATION BASE (FIB) - The FIB contains Layer 3 information, similar to the information found in an IP routing table. Additionally, an FIB contains information about multicast routes and directly connected hosts.
ADJACENCY TABLE - When a router is performing a route lookup using Cisco Express Forwarding (CEF), the Forwarding Information Base (FIB) references an entry in the adjacency table. The adjacency table entry contains the frame header information required by the router to properly form a frame. Therefore, an egress interface and a next-hop IP address would be in an adjacency entry for a multipoint interface, whereas a point-to-point interface would only require egress interface information.
DATA LINK CONNECTION IDENTIFIER (DLCI) - A DLCI is a locally significant identifier for a Frame Relay virtual circuit (VC).
VIRTUAL PATH IDENTIFIER/VIRTUAL CIRCUIT IDENTIFIER (VPI/VCI) - A VPI/VCI is a part of numbers identifying an ATM virtual circuit (VC).
ADMINISTRATIVE DISTANCE - An administrative distance is a measure of the believability of a routing protocol, with lower administrative distance being more believable. For example, Routing Information Protocol (RIP) has an administrative distance of 120, whereas Open Shortest Path First (OSPF) has an administrative distance of 110. Therefore, if a router ran both RIP and OSPF, and if both routing protocols knew of a route to reach a destination network, the router would install the OSPF-learned route into its IP routing table because of the preferable administrative distance of OSPF.
EIGRP INTERFACE TABLE - All the router interfaces that have been configured to participate in an Enhanced Interior Gateway Routing Protocol (EIGRP) routing process are listed in this table. However, if an interface has been configured as passive (that is, am interface that does not send routing information), it does not appear in this table.
EIGRP NEIGHBOR TABLE - This table lists the Enhanced Interior Gateway Routing Protocol (EIGRP) neighbors of a router (that is, neighboring routers from whom an EIGRP Hello message has been received). A neighbor is removed from this table if it has not been heard from for a period defined as the hold-time. Also, if an interface off of which a neighbor is known is removed from the EIGRP interface table because it goes down, the neighbor is removed from this table.
EIGRP TOPOLOGY TABLE - This table contains routes learned by an Enhanced Interior Gateway Routing Protocol (EIGRP) routing process. The best route for a network in this table becomes a candidate to be injected into the router's IP routing table. If multiple routes in this table have an equal metric, or if EIGRP's variance feature is configured, more than one route might become a candidate for injection into the IP routing table.
VARIANCE - Variance is an Enhanced Interior Gateway Protocol (EIGRP) feature that supports load balancing over unequal-cost path.
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