The only time EIGRP advertises its entire routing table is when it discovers a new neighbor and forms an adjacency with it through the exchange of Hello packets. When this happens, both neighbors advertise their entire routing tables to one another. After each has learned its neighbor’s routes, only changes to the routing table are propagated from then on.
Queries for an alternate route if no route can be found
The key to EIGRP’s speedy convergence is twofold
First ， EIGRP routers maintain a copy of all of their neighbors’ routes, which they use to calculate their own cost to each remote network.If the best path goes down, it may be as simple as examining the contents of the topology table to select the best replacement route.
The route table stores the routes that are currently used to make routing decisions. There would be separate copies of each of these tables for each protocol that is actively being supported by EIGRP, whether it’s IP, IPX, or AppleTalk.
Within an area, each router calculates the best/shortest path to every network in that same area.This calculation is based upon the information collected in the topology database and an algorithm called shortest path first (SPF)
After identifying the OSPF process, you need to identify the interfaces that you want to activate OSPF communications on, as well as the area in which each resides. This will also configure the networks you’re going to advertise to others.
A 0 octet in the wildcard mask indicates that the corresponding octet in the network must match exactly. On the other hand, a 255 indicates that you don’t care what the corresponding octet is in the network number.
Loopback interfaces are logical interfaces, which are virtual, software-only interfaces; they are not real router interfaces. Using loopback interfaces with your OSPF configuration ensures that an interface is always active for OSPF processes.
They can be used for diagnostic purposes as well as OSPF configuration. The reason you want to configure a loopback interface on a router is because if you don’t, the highest IP address on a router will become that router’s RID. The RID is used to advertise the routes as well as elect the DR and BDR.