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Cisco Catalyst Switch Module 3110 and 3012 for IBM BladeCenter Software Configuration Guide
OL-12189-01
Chapter 38 Configuring IP Unicast Routing
Configuring Stub Routing
Configuring Split Horizon
Routers connected to broadcast-type IP networks and using distance-vector routing protocols normally
use the split-horizon mechanism to reduce the possibility of routing loops. Split horizon blocks
information about routes from being advertised by a router on any interface from which that information
originated. This feature can optimize communication among multiple routers, especially when links are
broken.
Note In general, we do not recommend disabling split horizon unless you are certain that your application
requires it to properly advertise routes.
Beginning in privileged EXEC mode, follow these steps to disable split horizon on the interface:
To enable the split horizon mechanism, use the ip split-horizon interface configuration command.
Configuring Stub Routing
The stub routing feature reduces resource usage by moving routed traffic closer to the end user. The
switch supports Protocol-Independent Multicast (PIM) stub routing and Enhanced Interior Gateway
Routing Protocol (EIGRP) stub routing.
Stub routing is explained in these sections:
• Understanding PIM Stub Routing, page 38-26
• Configuring PIM Stub Routing, page 38-27
• Understanding EIGRP Stub Routing, page 38-29
• Configuring EIGRP Stub Routing, page 38-30
Understanding PIM Stub Routing
In a network using PIM stub routing, the only allowable route for IP traffic to the user is through a switch
that is configured with PIM stub routing. PIM passive interfaces are connected to Layer 2 access
domains, such as VLANs, or to interfaces that are connected to other Layer 2 devices. Only directly
connected multicast (IGMP) receivers and sources are allowed in the Layer 2 access domains. The PIM
passive interfaces do not send or process any received PIM control packets.
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
interface interface-id Enter interface configuration mode, and specify the interface to
configure.
Step 3
ip address ip-address subnet-mask Configure the IP address and the IP subnet.
Step 4
no ip split-horizon Disable split horizon on the interface.
Step 5
end Return to privileged EXEC mode.
Step 6
show ip interface interface-id Verify your entries.
Step 7
copy running-config startup-config (Optional) Save your entries in the configuration file.