are cisco certifications still worth it

are cisco certifications still worth it.The DV routing protocol has two functions that require information between neighboring routers.The first, routers need to send routing information in a particular message so that the sending router can advertise the routing information to the neighboring routers. For example, in Figure 9-3, R1 receives the RIP message and obtains the route. As discussed in Chapter 8, OSPF calls these messages link state updates (LSUs). both RIP and EIGRP happen to make their messages update messages.In addition. the router has to monitor at all times to make sure that every neighboring router is working properly. The way to do this is to periodically send and receive messages from neighboring routers. By quickly determining if an adjacent router has stopped working, the router can converge more quickly in order to use the router that is still working properly. Figure 9-4 Image resolution of the DV conceptAll routing protocols use some mechanism to monitor the state of neighboring routers. ospf uses Hell. messages for a relatively short period of time (10 seconds by default on many interfaces). and EIGRP also uses Hello messages and processes. But older versions of DV protocols, such as RIP, do not use separate Hello-type messages; they use the same update messages to advertise routing information and to know whether neighboring routers are still working. In other words, the function of informing routing information (and monitoring the status of neighboring routers) is accomplished with the same update messages.These older, basic DV routing protocols (such as RIP) send complete routing updates at regular intervals over a fairly short period of time. A full update means that a particular router uses one or more RIP update messages to inform all routers, regardless of whether that route has changed. By periodic, I mean that the router sends messages based on a timed interval (RIP uses 30 seconds).Figure 9-5 illustrates this concept using an Internet with two routers, three subnets, and a WAN subnet. The figure shows the router's full routing table and lists the periodic full routing updates sent by each router.The diagram gives a lot of information; take a little more time to study the individual details. For example, consider what information router R1 gets about subnet 172.30.22.0/24, and which subnet is connected to R2's interface G0/1?(1) R2's interface G0/1 has an IP address and is in the up/up state.(2) R2 has added a connected route for 172.30.22.0/24 to the routing table from interface G0/1 to R2.(3) R2 informs 172.30.22.0/24 of its route to R1, which means that R1 arrives on that subnet with a metric of metric 1 (that is, a hop count of 1).