Support Support Downloads Knowledge Base Juniper Support Portal Community

Knowledge Base

Search our Knowledge Base sites to find answers to your questions.

Ask All Knowledge Base Sites All Knowledge Base Sites JunosE Defect (KA)Knowledge BaseSecurity AdvisoriesTechnical BulletinsTechnotes Sign in to display secure content and recently viewed articles

How to use fail filters to bypass Unicast RPF check.

0

0

Article ID: KB27586 KB Last Updated: 18 Jun 2013Version: 1.0
Summary:
This article explains how to use unicast RPF-check fail filters in a dynamic profile in contrast to statically configured fail filter.

Symptoms:
If you have asynchronous routes that are failing due to unicast RPF check, you can use fail filters to bypass the failure.

The fail filter enables you to set criteria for packets you want to be passed in spite of failing the RPF check, such as DHCP packets, which are dropped by default.

Cause:
Unicast RPF helps ensure that a traffic source is legitimate (authorized) by comparing the source address of each packet that arrives on an interface to the forwarding-table entry for its source address. If the router uses the same interface that the packet arrived on to reply to the packet's source, this verifies that the packet originated from an authorized source, and the router forwards the packet. If the router does not use the same interface that the packet arrived on to reply to the packet's source, the packet might have originated from an unauthorized source, and the router discards the packet, or passes it to a fail filter.

Solution:
To configure a firewall fail filter:
***Items in <> are variable attributes which can be set according to network needs***

1. Create the filter.

[edit]
user@router# edit firewall family inet filter <filter_name>


2. Specify a term for the filter.

[edit firewall family inet filter <filter_name>]
user@router# edit term <term_name>


3. Configure the match conditions for the filter.

[edit firewall family inet filter <filter_name> term <term_name>]
user@router# set from <match_conditions>


4. Configure the actions to be taken for the matching packets.

[edit firewall family inet filter <filter_name> term <term_name>]
user@router# set then <action>


5. (Optional) Repeat Steps 3 and 4 for additional filter terms.

Related Links

Comment on this article > Affected Products Browse the Knowledge Base for more articles related to these product categories. Select a category to begin.

Getting Up and Running with Junos

Getting Up and Running with Junos Security Alerts and Vulnerabilities Product Alerts and Software Release Notices Problem Report (PR) Search Tool EOL Notices and Bulletins JTAC User Guide Customer Care User Guide Pathfinder SRX High Availability Configurator SRX VPN Configurator Training Courses and Videos End User Licence Agreement Global Search