1.The main contents of  CCNP certification include routing, switching and troubleshooting.
2.To learn routing, you should master three knowledge points: router, routing protocol and routing table.
3.The function of a router is routing (addressing). It is realized by looking up the routing table and forwarding data.
4.How a router generates a routing table: it generates a routing table by running a routing protocol.
5.Dynamic routing protocol:
Distance Vector: RIP, EIGRP, BGP
Link State: OSPF, IS-IS
6.Routers are divided into control layer and forwarding layer.
The control level generates RIB (Routing Information Base) and routing table. The routing table stores all routing information, regardless of the specific routing protocol. All routing protocols store their routes here. As long as the routing protocol running on the router learns a new route, it will be placed in the routing table. for more check CCNP certification.
The forwarding level generates FIB (Forwarding Information Base) and forwarding table. It is configured to determine how to forward based on the network prefix of the IP packet. Different manufacturers have different technologies. Cisco uses CEF – Cisco Express Forwarding. In actual work, generally, the routing table is copied to the forwarding table. When the data comes in, it is judged according to the forwarding table.
7.Routing table:
Each router has at least one separate routing table (unicast routing table, or global routing table).
Routers that support multicast also have multicast routing tables.
Conditions for judging the same route: same prefix, same mask and same next hop.
8.In forwarding data packets, the router follows three principles:
Longest mask matching principle;
If the masks are the same, the AD value (Administrative Distance) is compared, and the smaller the AD, the better. This usually happens between different routing protocols;
If the AD value is the same, the metric value is compared. The smaller the metric value, the priority.
9.Static route:
Static route is a route entry manually added by the administrator.
When the next hop or outgoing interface of a static route does not exist in the routing table, the route will not be displayed in the routing table, but it still exists.
Static routes can be recursively queried.
The AD value of a static route can be adjusted manually as needed, so that this static route can be used as a backup of other routes or be better than other routes.
Static routes can be tagged.
Multiple static routes with the same AD value can achieve equivalent load balancing.
Floating static routing can be combined with IP SLA technology to achieve high availability.
The advantage of static routing is: stability.
The disadvantages of static routing are: weak scalability and insufficient flexibility.
Format: IP route, destination, netmask, next hop.
10.Dynamic routing protocol:
The dynamic routing protocol is run between routers, so that routers can exchange various kinds of information and automatically learn the routes in the network.
Dynamic routing protocols can be divided into Internal Gateway Protocol (IGP) and External Gateway Protocol (EGP) according to protocol hierarchy.
According to the working principle of the protocol, Dynamic Routing Protocols can be divided into Distance Vector Protocol and Link State Protocol.
As for dynamic routing protocol metrics, each protocol has a different definition.
