Configuring The Number Of Equal-Cost Routing Paths - Cisco Catalyst 3750 Software Configuration Manual

Chapter 28 Configuring IP Unicast Routing
The two main components in CEF are the distributed FIB and the distributed adjacency tables.
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CEF is enabled globally by default. If for some reason it is disabled, you can re-enable it by using the ip
cef global configuration command.
The default configuration is CEF enabled on all Layer 3 interfaces.
Caution Although the no ip route-cache cef interface configuration command to disable CEF on an interface is
visible in the CLI, we strongly recommend that you do not disable CEF on interfaces.
Beginning in privileged EXEC mode, follow these steps to enable CEF globally and on an interface in
case, if, for some reason, it has been disabled:
Command
Step 1 configure terminal
Step 2
ip cef
Step 3
interface interface-id
Step 4 ip route-cache cef
Step 5 end
Step 6
show ip cef
Step 7 show cef interface [interface-id]
Step 8 show adjacency
Step 9 copy running-config startup-config

Configuring the Number of Equal-Cost Routing Paths

When a router has two or more routes to the same network with the same metrics, these routes can be
thought of as having an equal cost. The term parallel path is another way to refer to occurrences of
equal-cost routes in a routing table. If a router has two or more equal-cost paths to a network, it can use
them concurrently. Parallel paths provide redundancy in case of a circuit failure and also enable a router
to load balance packets over the available paths for more efficient use of available bandwidth.
Although the router automatically learns about and configures equal-cost routes, you can control the
maximum number of parallel paths supported by an IP routing protocol in its routing table.
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The FIB is similar to a routing table or information base and maintains a mirror image of the
forwarding information in the IP routing table. When routing or topology changes occur in the
network, the IP routing table is updated, and those changes are reflected in the FIB. The FIB
maintains next-hop address information based on the information in the IP routing table. Because
the FIB contains all known routes that exist in the routing table, CEF eliminates route cache
maintenance, is more efficient for switching traffic, and is not affected by traffic patterns.
Nodes in the network are said to be adjacent if they can reach each other with a single hop across a
link layer. CEF uses adjacency tables to prepend Layer 2 addressing information. The adjacency
table maintains Layer 2 next-hop addresses for all FIB entries.
Purpose
Enter global configuration mode.
Enable CEF operation.
Enter interface configuration mode, and specify the Layer 3
interface to configure.
Enable CEF on the interface.
Return to privileged EXEC mode.
Display the CEF status on all interfaces.
Display detailed CEF information for all interfaces or the
specified interface.
Display CEF adjacency table information.
(Optional) Save your entries in the configuration file.
Catalyst 3750 Metro Switch Software Configuration Guide
Configuring Protocol-Independent Features
28-87