What is Routing & Cisco Routing Table

What is Routing & Cisco Routing Table

This blog post is an introduction on What is Routing & what is Cisco Routing Table. You will also learn about the how hosts are forwarded the packets in networking.

What is Routing?

The routing is the process of moving a data packet from source to destination base on the IP address and router device is performed. Routing is a key feature of the Internet because it allows messages to pass from one computer to another and eventually reach the destination machine. Each intermediate computer performs the routing by passing the message to the next computer.

How computer forward a packet in Network?

Another function of the network layer is to direct packets between hosts. There are three types of destination:

1. To itself (IPv4 address 127.0.0.1): Named “loopback interface”
2. A local host (is a host that is on the same local network as the sending host)
3. A remote host (is a host on a remote network).

Devices that are not in the local network segment are called " remote I / O module ". When a source device sends a packet to a remote destination device, the help of routers and routing is needed. Routing is the process of identifying the best route to reach a destination. The router connected to the local network segment is called the default gateway .

What is default Gateway?

The default gateway is the router interface connected to the LAN. It is used only when a host must forward packets to a remote network.

1. The default gateway is the network device that can route traffic to other networks.
2. It has a local IP address in the same address range as other hosts on the network
3. You can carry data and forward it.
4. It is the router that can route traffic outside the local network.

HOST ROUTING TABLES

Use the following commands to display the host routing table on a Windows machine:

route print
netstat -r

Three sections related to the current TCP / IP network connections are shown:

1. Interface list: Displays a list of media access control (MAC) addresses and the assigned interface number of each interface with network connection capability on the host, including Ethernet, Wi-Fi and Bluetooth adapters.
2. IPv4 route table : This is a list of all known IPv4 routes, including direct connections, local networks and default local routes.
3. IPv6 route table : It is a list of all known IPv6 routes, including direct connections, local networks and default local routes.

What is Cisco Routing Table?

When a host sends a packet to another, it uses its routing table to determine where to send it. The routing table of a router stores:

1. Directly connected routes: These routes come from active router interfaces. Routers add a directly connected route when an interface is configured with an IP address and activated. Each of the router interfaces is connected to a different network segment.
2. Remote routes: These routes come from remote networks connected to other routers. The network administrator can configure the routes to these networks manually on the local router or these routes can be configured dynamically by allowing the local router to exchange routing information with other routers.
3. Default route : Like a host, routers also use the default routes as a last resort if there is no other route to reach the desired network in the routing table.

IPV4 ROUTER ROUTING TABLE

Use the following command to display the routing table on a Cisco router.

show ip route

The router's routing table stores the network routes on which the router has knowledge and also has information on how the route was obtained, its confidence and its rating.
It also indicates which interface should be used to reach that specific destination.
When a packet arrives at the router interface, the router examines the packet header to determine the destination network. If the destination network has a route in the routing table, the router sends the packet using the information specified in the routing table. If there are two or more possible routes to reach the same destination, the metric is used to decide which one appears in the routing table.

• " D ": means EIGRP, connection with remote networks. 
• " C ": means "connected", connection with our connected network routes.
• " L ": means "link-local address", this is the address of the local interface, connected directly to the router interface.

ROUTING TABLE ENTRIES DIRECTLY CONNECTED

L : indicates that it is a local interface. This is the IPv4 address of the router interface.

C : Identifies a network directly connected and created automatically when an interface with an IP address is configured and activated.

REMOTE NETWORK ROUTING TABLE ENTRIES

• Remote routes contain the address of the intermediate network device that will be used to reach the destination.
• Remote destinations cannot be accessed directly.

The next hop address 

The next hop address is the address of the intermediate device used to reach a specific remote destination.

Routers cannot send packets without a route to the destination network in the routing table . If a route representing the destination network is not in the routing table, the packet is discarded (that is, it is not sent). Routers can also include a default route to generate a gateway of last resort. The default route can be set manually or obtained dynamically.