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Example: Configuring a Filter to Count IP Options Packets

This example shows how use a stateless firewall filter to count individual IP options packets:

Requirements

This example uses 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. This interface enables you to apply an IPv4 firewall filter (standard or service filter) that can use the count, log, and syslog nonterminating actions on packets that match a specific ip-option value without having to also use the discard terminating action.

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

Overview

In this example, you use a stateless firewall filter to count IP options packets but not block any traffic. Also, the filter logs packets that have loose or strict source routing.

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:

CLI Quick Configuration

To quickly configure this example, copy the following configuration commands into a text file, remove any line breaks, and then paste the commands into the CLI at the [edit] hierarchy level.

Configure the Stateless Firewall Filter

Step-by-Step Procedure

To configure the stateless firewall filter ip_option_filter:

  1. Create the stateless firewall filter ip_option_filter.

  2. Configure the first term to count, log, and accept packets with the strict_source_route IP optional header field.

  3. Configure the next term to count, log, and accept packets with the loose-source-route IP optional header field.

  4. Configure the next term to count and accept packets with the record-route IP optional header field.

  5. Configure the next term to count and accept packets with the timestamp IP optional header field.

  6. Configure the next term to count and accept packets with the router-alert IP optional header field.

  7. Create the last term to accept any packet without incrementing any counters.

Apply the Stateless Firewall Filter to a Logical Interface

Step-by-Step Procedure

To apply the stateless firewall filter to a logical interface:

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

  2. Configure the interface address for the logical interface.

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

Confirm and Commit Your Candidate Configuration

Step-by-Step Procedure

To confirm and then commit your candidate configuration:

  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.

  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.

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

Verification

To confirm that the configuration is working properly, enter the show firewall filter ip_option_filter operational mode command. You can also display the log and individual counters separately by using the following forms of the command:

  • show firewall counter strict_source_route

  • show firewall counter loose_source_route

  • show firewall counter record_route

  • show firewall counter timestamp

  • show firewall counter router_alert

  • show firewall log