As if you have two FastEthernet ports on the router, one may be for subnet We do not want the broadcasts going from the The router will stop that and keep the broadcasts from propagating. But at the same time, it will figure out how to route data from the Ok, so stick with me and you will see how this would look in the real world and not just on your CCNA exam.
Remember that we said above that routers do not normally come with a bunch of FastEthernet ports and that is because their job is to route data between networks. Does this diagram make more sense now?
For example, a router provides you with the internet access by connecting your LAN with the Internet. If two hosts from different networks want to communicate with each other, they will need a router between them. Consider the following example:. We have a network of three computers. Basically IP routing in router is a process of packet transfer between different networks. Selection of path and interface to exit a data packet is based on IP routing.
IP routing works on various routing and routed protocols. Routing protocols helps router to build and maintain the routing table in routers. The Routing protocols inform the router about the networks. Any change in the network required to be update in the routing tables of all routers. This task is carried out by the routing protocols. Routing protocols help the routers to select the best path to exit the data packets. Routing protocols further divided into distance vector , link state and hybrid protocols.
These all routing protocols update the routing table of all routers in the network. Routed protocols do not update or maintain the routing table in a router. The Routed protocols are responsible for flow of data packets from one network to another network.
Routed protocols sends the data packets to correct exit interface of the router. Routed protocols configured on interfaces of the router. Routed protocols are basically addressing schema of the interfaces of router. Router identify the destination network of a data packet and send the data packet to correct exit interface. The concept of subnetting takes place in routed protocols.
We know the role and function of router in network. A router connects two or more networks for data packet forwarding. When a data packet received on any interface of router, it will examine the header section of the data packet for destination IP address. So the routing table contains the network layer intelligence that tells the router how to forward packets to remote destinations. Initially, that routing table is made up of networks that are directly connected to the particular router. They are obviously shown as directly connected networks, after that the way to learn about remote destinations is by either populating the routing table with static routes in which an administrator will tell the router how to get to the destination or by populating the routing table via routing table advertisements coming from other routers.
So routers are gossipy and they will tell each other information that allows them to know about all the gossip in the network. In both cases, static and dynamic routing notice how routers use the reserved subnet addresses or network addresses that contain all 0s in the host portion of the IP address. In this case, we are talking about a classless subnetted class A address. Network 10 split into subnets similar to a class C. However, in all cases here, the host portion of the address, the fourth byte is all 0s and that represents that subnet or network itself.
In other words, these are destination networks or subnets. In the case of remote destinations, the routing table entries show what the next hop is in order to reach that destination. In this case, in order to reach These are categories of routing table entries that could be populated either dynamically or statically. Some of them are born with the router. As soon as the router boots up, it will identify its directly connected active networks and interfaces and define them as reachable destinations, only because of the fact that the router is directly attached or connected to it.
Now that is pretty smart, but even smarter is the fact that the routers will communicate with each other, exchange routing information via dynamic routing protocols like OSPF or EIGRP, and then learn not only about those destinations, but also adjust to changes on those destinations. Routing protocols will be able to identify topology changes and tell each other about them.
Soon enough, entries will appear and disappear from the routing table according to availability; again, an administrator could come in and manually insert static entries. This is sometimes not recommended because they will be static and they will not adjust to network changes; in other words, if the entry or the destination goes down, the entry will remain there and the router will still forward packets to a destination that is not available.
Perhaps a special case of a static route is the default route. Although they can also be learned dynamically, static defaults are used when no explicit route to a destination is known and so this is the entry that identifies all unknown destinations. The router will say, "If I do not know about a certain destination, I will forward a packet to someone that does, typically another router. Optimal path selection depends on what is known as the cost to reach a destination across a certain path.
Again, the cost of a path is made up of incremental costs for each hop along the path. The cost is also known as metric, and different routing protocols will consider different criteria in order to define the metric.
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