On a Cisco IOS router, the “show ip route” command displays 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 use (do) 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 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 decide which route is best.
Figure 1 shows the topology diagram which is consists of two router Rawalpindi and Peshawar. You can download the topology from here download from here. Figure 2 shows the routing table on the 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 configured with an IP address and activated.
- L- Identifies that this is a local interface and 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 seem 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 learned (C, L), the destination network (192.168.3.0) and outgoing interface (Fast Ethernet 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 an explanation of the route.
Identifies how the route 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.
Identifies the destination network for the local router.
[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.
[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.
Via 192.168.10.1 is the IP address of the next router. This IP is next-hop for this route.
This is the last time when the route updated (hours: minutes: seconds).
Last entry is the outgoing interface to use to send a packet toward the destination.