Configure Reverse Path Checking on a VLAN

Before you begin

Before you can configure reverse path checking on a VLAN, you must assign a valid IP address to the selected VLAN.

About this task

Configure reverse path checking on a VLAN to determine if a packet IP address is verifiable. Use reverse path checking to reduce the problems that are caused by the introduction of malformed or forged (spoofed) IP source addresses into a network. After you enable reverse path checking, the switch performs a reverse path check to determine if the packet IP address is verifiable. If the address is not verifiable, the system discards the packet.

Reverse path checking operates in one of two modes:

exist-only mode
strict mode

Procedure

In the navigation pane, expand Configuration > VLAN.
Click VLANs.
Click the VLAN on which you want to configure reverse path checking.
In the toolbar, click IP.
Click the Reverse Path Checking tab.
Select the Enable box to enable reverse path checking.
Select exist-only or strict.
Click Apply.

Reverse Path Checking field descriptions

Use the data in the following table to use the Reverse Path Checking tab.


Name	Description
Enable	Enables reverse path checking on the selected VLAN.
Mode	Specifies the mode for reverse path checking. The modes are exist-only—reverse path checking checks whether the incoming packet source IP address exists in the routing table. If reverse path checking finds the source IP entry, the packet is forwarded; otherwise, the packet is discarded. strict—reverse path checking checks whether the incoming packet source IP address exists in routing table. If reverse path checking does not find the source IP entry, then the packet is dropped. Otherwise, reverse path checking further checks if the source IP interface matches the incoming interface of the packet. If they match, then the packet is forwarded. Otherwise, the packet is discarded. The default is exist-only.