Split-Horizon Poison - Enterasys SecureStack C2 C2G170-24 Configuration Manual

Mode
Router configuration: C2(su)‐>router(Config‐router)#
Usage
By default, RIP version 2 supports automatic route summarization, which summarizes
subprefixes to the classful network boundary when crossing network boundaries. Disabling
automatic route summarization enables CIDR, allowing RIP to advertise all subnets and host
routing information on the SecureStack C2 device. To verify which routes are summarized for an
interface, use the show ip route command as described in "show ip route" on page 19‐15. The
reverse of the command re‐enables automatic route summarization. By default, RIP auto‐
summarization affects both RIPv1 and RIPv2 routes.
Example
This example shows how to disable RIP automatic route summarization:
C2(su)->router(Config)#router rip
C2(su)->router(Config-router)#no auto-summary

split-horizon poison

Use this command to enable or disable split horizon poison‐reverse mode for RIP packets. The no
form of this command disables split horizon poison reverse.
Syntax
split-horizon poison
no split-horizon poison
Parameters
None.
Defaults
None.
Mode
Router configuration: C2(su)‐>router(Config‐router)#
Usage
Split horizon prevents a network from being advertised out the same interface it was received on.
This function is disabled by default.
Example
This example shows how to disable split horizon poison reverse for RIP packets transmitted on
the VLAN 1 interface:
C2(su)->router(Config)#router rip
C2(su)->Router1(Config-router)#no split-horizon poison
Note: This command is necessary for enabling CIDR for RIP on the SecureStack C2 device.
split-horizon poison
SecureStack C2 Configuration Guide 20-7