Chapter 17
| General IP Routing
Displaying the Routing Table
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Figure 450: Displaying Static Routes
Displaying the Routing Table
Use the IP > Routing > Routing Table (Show Information) page to display all routes
that can be accessed via local network interfaces, through static routes, or through
a dynamically learned route. If route information is available through more than
one of these methods, the priority for route selection is local, static, and then
dynamic (except when the distance parameter of a dynamic route is set to a value
that makes its priority exceed that of a static route). Also note that the route for a
local interface is not enabled (i.e., listed in the routing table) unless there is at least
one active link connected to that interface.
Command Usage
◆ The Forwarding Information Base (FIB) contains information required to
forward IP traffic. It contains the interface identifier and next hop information
for each reachable destination network prefix based on the IP routing table.
When routing or topology changes occur in the network, the routing table is
updated, and those changes are immediately reflected in the FIB.
The FIB is distinct from the routing table (or, Routing Information Base – RIB),
which holds all routing information received from routing peers. The FIB
contains unique paths only. It does not contain any secondary paths. A FIB
entry consists of the minimum amount of information necessary to make a
forwarding decision on a particular packet. The typical components within a
FIB entry are a network prefix, a router (i.e., VLAN) interface, and next hop
information.
◆ The Routing Table (and the “show ip route” command described in the
CLI Reference Guide) only displays routes which are currently accessible for
forwarding. The router must be able to directly reach the next hop, so the VLAN
interface associated with any dynamic or static route entry must be up. Note
that routes currently not accessible for forwarding, may still be displayed by
using the “show ip route database” command.
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