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Example: Configuring a Filter to Count and Discard IP Options Packets

Requirements

No special configuration beyond device initialization is required before configuring this example.

Because the filter term matches on any IP option value, the filter term can use the count nonterminating action without the discard terminating action or (alternatively) without requiring an interface on a 10-Gigabit Ethernet Modular Port Concentrator (MPC), 60-Gigabit Ethernet MPC, 60-Gigabit Queuing Ethernet MPC, or 60-Gigabit Ethernet Enhanced Queuing MPC on an MX Series router.

Overview

In this example, you use a standard stateless firewall filter to count and discard packets that include any IP option value but accept all other packets.

The IP option header field is an optional field in IPv4 headers only. The ip-options and ip-options-except match conditions are supported for standard stateless firewall filters and service filters only.

Note: On M and T series routers, firewall filters cannot count ip-options packets on a per option type and per interface basis. A limited work around is to use the show pfe statistics ip options command to see ip-options statistics on a per Packet Forwarding Engine (PFE) basis. See show pfe statistics ip for sample output.

Configuration

The following example requires you to navigate various levels in the configuration hierarchy. For information about navigating the CLI, see Using the CLI Editor in Configuration Mode.

To configure this example, perform the following tasks:

• Configure the Stateless Firewall Filter
• Apply the Stateless Firewall Filter to a Logical Interface
• Confirm and Commit Your Candidate Configuration

CLI Quick Configuration

Configure the Stateless Firewall Filter

Step-by-Step Procedure

1. Create the stateless firewall filter block_ip_options.

   [edit]user@host# edit firewall family inet filter block_ip_options

2. Configure the first term to count and discard packets that include any IP options header fields.

   [edit firewall family inet filter block_ip_options]user@host# set term 10 from ip-options anyuser@host# set term 10 then count option_anyuser@host# set term 10 then discard

3. Configure the other term to accept all other packets.

   [edit firewall family inet filter block_ip_options]user@host# set term 999 then accept

Apply the Stateless Firewall Filter to a Logical Interface

Step-by-Step Procedure

1. Configure the logical interface to which you will apply the stateless firewall filter.

   [edit]user@host# edit interfaces ge-0/0/1 unit 0 family inet

2. Configure the interface address for the logical interface.

   [edit interfaces ge-0/0/1 unit 0 family inet]user@host# set address 10.1.2.3/30

3. Apply the stateless firewall filter to the logical interface.

   [edit interfaces ge-0/0/1 unit 0 family inet]user@host# set filter input block_ip_options

Confirm and Commit Your Candidate Configuration

Step-by-Step Procedure

1. Confirm the configuration of the stateless firewall filter by entering the show firewall configuration mode command. If the command output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

   [edit]user@host# show firewall

   family inet {filter block_ip_options {term 10 {from {ip-options any;}then {count option_any;discard;}}term 999 {then accept;}}}

2. Confirm the configuration of the interface by entering the show interfaces configuration mode command. If the command output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

   [edit]user@host# show interfaces

   ge-0/0/1 {unit 0 {family inet {filter {input block_ip_options;}address 10.1.2.3/30;}}}

3. If you are done configuring the device, commit your candidate configuration.

   [edit]user@host# commit

Verification

To confirm that the configuration is working properly, enter the show firewall filter block_ip_options operational mode command. To display the count of discarded packets separately, enter the show firewall count option_any form of the command.