IPv4 Router Routing Table

On a Cisco IOS router, the "show ip route" command can be used to display the router’s routing table, as shown in the figure. The show command is working in User Privilege Mode. If we want to use show commands in global configuration mode then (do) will be used before show command. The router routing table provides the following information:

• The routing information for directly-connected networks


• The routing information for remote networks.


• Information how the route was learned.


• The reliability of the route.


• Rating of the route.


• When was the route last updated?


• Which interface to use to reach the requested destination?

When a packet received at the router interface, the router read the packet header to decide the destination network for the packet. If the destination network matches a route in the routing table, then the router forwards the packet using the information in the routing table. If there are two or more possible routes to the same destination, the metric is used to make a decision which route is best.

Figure 1 shows the topology diagram which is consists of two router Rawalpindi and Peshawar. Topology in Packet Tracer can be download from here. Figure 2 shows the routing table on Rawalpindi router.

Directly Connected Routing Table Entries

When a router interface is configured with an IPv4 address and is activated with no shutdown command, the following two routing table entries are automatically created:

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


• L- Identifies that this is a local interface and also show the IPv4 address of the interface on the router.

Figure 2 describes the routing table entries on Rawalpindi for the directly-connected networks 192.168.3.0, 192.168.4.0 and 192.168.10.0 These entries were automatically added to the routing table when these interfaces were configured and activated with no shutdown command. Local interface entries did not appear in routing tables previous to IOS Release 15. The IOS version of the router Rawalpindi is 12.4. so Its does not display local interface entries.

The routing table entries show that how the network was learned (C, L), the destination network for example (192.168.3.0) and outgoing interface (FastEthernet 0/0)

Remote Network Routing Table Entries

As we know that router typically has multiple interfaces configured. The routing table stores information about both directly-connected networks and remote networks. Figure 2 also shows the result of Remote Network Routing Table Entries.

The figure shows the Rawalpindi route to remote network 192.168.0.0 and 192.168.1.0. Following are the explanation of the route.

Source

Identifies how the route was learned by the router. Common routing sources include S (static route), D (Enhanced Interior Gateway Routing Protocol or EIGRP), and O (Open Shortest Path First or OSPF). Other route sources are also shown in the figure.

Destination Network

Identifies the destination network for the local router.

Administrative Distance

[90/2172416] 90 is the administrative distance of the route. It shows the trustworthiness of the router source. Lower values indicate increased the trustworthiness of the route source.

Metric

[90/2172416] The value in red show the metric of the route. Metric Identifies the value assigned to reach the remote network. Lower values indicate preferred routes.

Next-Hop

Via 192.168.10.1 is the IP address of the next router. This IP is next-hop for this route.

Route Timestamp

This is the last time when the route was updated (hours: minutes: seconds).

Outgoing interface

Last entry is the outgoing interface to use to forward a packet toward the final destination.