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Example: Configuring Filter-Based Forwarding on Logical Systems

Requirements

In this example, no special configuration beyond device initialization is required.

Overview

Filter-based forwarding is supported for IP version 4 (IPv4) and IP version 6 (IPv6).

Use filter-based forwarding for service provider selection when customers have Internet connectivity provided by different ISPs yet share a common access layer. When a shared media (such as a cable modem) is used, a mechanism on the common access layer looks at Layer 2 or Layer 3 addresses and distinguishes between customers. You can use filter-based forwarding when the common access layer is implemented using a combination of Layer 2 switches and a single router.

With filter-based forwarding, all packets received on an interface are considered. Each packet passes through a filter that has match conditions. If the match conditions are met for a filter and you have created a routing instance, filter-based forwarding is applied to a packet. The packet is forwarded based on the next hop specified in the routing instance. For static routes, the next hop can be a specific LSP.

Note: Source-class usage filter matching and unicast reverse-path forwarding checks are not supported on an interface configured with filter-based forwarding (FBF).

To configure filter-based forwarding, perform the following tasks:

• Create a match filter on an ingress router or switch. To specify a match filter, include the filter filter-name statement at the [edit firewall] hierarchy level. A packet that passes through the filter is compared against a set of rules to classify it and to determine its membership in a set. Once classified, the packet is forwarded to a routing table specified in the accept action in the filter description language. The routing table then forwards the packet to the next hop that corresponds to the destination address entry in the table.
• Create routing instances that specify the routing table(s) to which a packet is forwarded, and the destination to which the packet is forwarded at the [edit routing-instances] or [edit logical-systems logical-system-name routing-instances] hierarchy level. For example:
  [edit]

  routing-instances {routing-table-name1 {instance-type forwarding;routing-options {static {route 0.0.0.0/0 nexthop 10.0.0.1;}}}routing-table-name2 {instance-type forwarding;routing-options {static {route 0.0.0.0/0 nexthop 10.0.0.2;}}}}
• Create a routing table group that adds interface routes to the forwarding routing instances used in filter-based forwarding (FBF), as well as to the default routing instance inet.0. This part of the configuration resolves the routes installed in the routing instances to directly connected next hops on that interface. Create the routing table group at the [edit routing-options] or [edit logical-systems logical-system-name routing-options] hierarchy level.

Note: Specify inet.0 as one of the routing instances that the interface routes are imported into. If the default instance inet.0 is not specified, interface routes are not imported into the default routing instance.

This example shows a packet filter that directs customer traffic to a next-hop router in the domains, SP 1 or SP 2, based on the packet’s source address.

If the packet has a source address assigned to an SP 1 customer, destination-based forwarding occurs using the sp1-route-table.inet.0 routing table. If the packet has a source address assigned to an SP 2 customer, destination-based forwarding occurs using the sp2-route-table.inet.0 routing table. If a packet does not match either of these conditions, the filter accepts the packet, and destination-based forwarding occurs using the standard inet.0 routing table.

One way to make filter-based forwarding work within a logical system is to configure the firewall filter on the logical system that receives the packets. Another way is to configure the firewall filter on the main router or switch and then reference the logical system in the firewall filter. This example uses the second approach. The specific routing instances are configured within the logical system. Because each routing instance has its own routing table, you have to reference the routing instances in the firewall filter, as well. The syntax looks as follows:

Figure 1 shows the topology used in this example.

On Logical System P1, an input filter classifies packets received from Logical System PE3 and Logical System PE4. The packets are routed based on the source addresses. Packets with source addresses in the 10.1.1.0/24 and 10.1.2.0/24 networks are routed to Logical System PE1. Packets with source addresses in the 10.2.1.0/24 and 10.2.2.0/24 networks are routed to Logical System PE2.

Figure 1: Logical Systems with Filter-Based Forwarding

To establish connectivity, OSPF is configured on all of the interfaces. For demonstration purposes, loopback interface addresses are configured on the routing devices to represent networks in the clouds.

The CLI Quick Configuration section shows the entire configuration for all of the devices in the topology. The Configuring the Routing Instances on the Logical System P1 and Configuring the Firewall Filter on the Main Router sections shows the step-by-step configuration of the ingress routing device, Logical System P1.

Configuration

CLI Quick Configuration

To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.

Configuring the Firewall Filter on the Main Router

Step-by-Step Procedure

1. Configure the source addresses for SP1 customers.
   [edit firewall filter classify-customers term sp1-customers]user@host# set from source-address 10.1.1.0/24user@host# set from source-address 10.1.2.0/24
2. Configure the actions that are taken when packets are received with the specified source addresses.

   To track the action of the firewall filter, a log action is configured. The sp1-route-table.inet.0 routing table on Logical System P1 routes the packets.

   [edit firewall filter classify-customers term sp1-customers]user@host# set then loguser@host# set then logical-system P1 routing-instance sp1-route-table
3. Configure the source addresses for SP2 customers.
   [edit firewall filter classify-customers term sp2-customers]user@host# set from source-address 10.2.1.0/24user@host# set from source-address 10.2.2.0/24
4. Configure the actions that are taken when packets are received with the specified source addresses.

   To track the action of the firewall filter, a log action is configured. The sp2-route-table.inet.0 routing table on Logical System P1 routes the packet.

   [edit firewall filter classify-customers term sp2-customers]user@host# set then loguser@host# set then logical-system P1 routing-instance sp2-route-table
5. Configure the action to take when packets are received from any other source address.

   All of these packets are simply accepted and routed using the default IPv4 unicast routing table, inet.0.

   [edit firewall filter classify-customers term default]user@host# set then accept

Configuring the Routing Instances on the Logical System P1

Step-by-Step Procedure

1. Configure the interfaces on the logical system.

   [edit logical-systems P1 interfaces lt-1/2/0]user@host# set unit 10 encapsulation ethernetuser@host# set unit 10 peer-unit 9user@host# set unit 10 family inet address 172.16.0.10/30
   user@host# set unit 13 encapsulation ethernetuser@host# set unit 13 peer-unit 14user@host# set unit 13 family inet address 172.16.0.13/30
   user@host# set unit 17 encapsulation ethernetuser@host# set unit 17 peer-unit 18user@host# set unit 17 family inet address 172.16.0.17/30
2. Assign the classify-customers firewall filter to router interface lt-1/2/0.10 as an input packet filter.
   [edit logical-systems P1 interfaces lt-1/2/0]user@host# set unit 10 family inet filter input classify-customers

3. Configure connectivity, using either a routing protocol or static routing.

   As a best practice, disable routing on the management interface.

   [edit logical-systems P1 protocols ospf area 0.0.0.0]user@host# set interface alluser@host# set interface fxp0.0 disable

4. Create the routing instances.

   These routing instances are referenced in the classify-customers firewall filter.

   The forwarding instance type provides support for filter-based forwarding, where interfaces are not associated with instances. All interfaces belong to the default instance, in this case Logical System P1.

   [edit logical-systems P1 routing-instances]user@host# set sp1-route-table instance-type forwarding
   user@host# set sp2-route-table instance-type forwarding

5. Resolve the routes installed in the routing instances to directly connected next hops.

   [edit logical-systems P1 routing-instances]user@host# set sp1-route-table routing-options static route 0.0.0.0/0 next-hop 172.16.0.13
   user@host# set sp2-route-table routing-options static route 0.0.0.0/0 next-hop 172.16.0.17

6. Group together the routing tables to form a routing table group.

   The first routing table, inet.0, is the primary routing table, and the additional routing tables are the secondary routing tables.

   The primary routing table determines the address family of the routing table group, in this case IPv4.

   [edit logical-systems P1 routing-options]user@host# set rib-groups fbf-group import-rib inet.0user@host# set rib-groups fbf-group import-rib sp1-route-table.inet.0user@host# set rib-groups fbf-group import-rib sp2-route-table.inet.0
7. Apply the routing table group to OSPF.

   This causes the OSPF routes to be installed into all the routing tables in the group.

   [edit logical-systems P1 protocols ospf]user@host# set rib-group fbf-group

8. If you are done configuring the device, commit the configuration.

   [edit]user@host# commit

Results

Confirm your configuration by issuing the show firewall and show logical-systems P1 commands.

Verification

Confirm that the configuration is working properly.

Pinging with Specified Source Addresses

Purpose

Send some ICMP packets across the network to test the firewall filter.

Action

1. Log in to Logical System PE3.
   user@host> set cli logical-system PE3

   Logical system: PE3

2. Run the ping command, pinging the lo0.3 interface on Logical System PE1.

   The address configured on this interface is 1.1.1.1.

   Specify the source address 10.1.2.1, which is the address configured on the lo0.1 interface on Logical System PE3.

   user@host:PE3> ping 1.1.1.1 source 10.1.2.1

   PING 1.1.1.1 (1.1.1.1): 56 data bytes
   64 bytes from 1.1.1.1: icmp_seq=0 ttl=62 time=1.444 ms
   64 bytes from 1.1.1.1: icmp_seq=1 ttl=62 time=2.094 ms
   ^C
   --- 1.1.1.1 ping statistics ---
   2 packets transmitted, 2 packets received, 0% packet loss
   round-trip min/avg/max/stddev = 1.444/1.769/2.094/0.325 ms

3. Log in to Logical System PE4.
   user@host:PE3> set cli logical-system PE4

   Logical system: PE4

4. Run the ping command, pinging the lo0.4 interface on Logical System PE2.

   The address configured on this interface is 2.2.2.2.

   Specify the source address 10.2.1.1, which is the address configured on the lo0.2 interface on Logical System PE4.

   user@host:PE4> ping 2.2.2.2 source 10.2.1.1

   PING 2.2.2.2 (2.2.2.2): 56 data bytes
   64 bytes from 2.2.2.2: icmp_seq=0 ttl=62 time=1.473 ms
   64 bytes from 2.2.2.2: icmp_seq=1 ttl=62 time=1.407 ms
   ^C
   --- 2.2.2.2 ping statistics ---
   2 packets transmitted, 2 packets received, 0% packet loss
   round-trip min/avg/max/stddev = 1.407/1.440/1.473/0.033 ms

Meaning

Sending these pings activates the firewall filter actions.

Verifying the Firewall Filter

Purpose

Make sure the firewall filter actions take effect.

Action

1. Log in to Logical System P1.
   user@host> set cli logical-system P1

   Logical system: P1

2. Run the show firewall log command on Logical System P1.
   user@host:P1> show firewall log

   Log :
   Time      Filter    Action Interface     Protocol        Src Addr            Dest Addr
   13:52:20  pfe       A      lt-1/2/0.10   ICMP            10.2.1.1            2.2.2.2
   13:52:19  pfe       A      lt-1/2/0.10   ICMP            10.2.1.1            2.2.2.2
   13:51:53  pfe       A      lt-1/2/0.10   ICMP            10.1.2.1            1.1.1.1
   13:51:52  pfe       A      lt-1/2/0.10   ICMP            10.1.2.1            1.1.1.1