Help us improve your experience.

Let us know what you think.

Do you have time for a two-minute survey?

 
 

Configuring PIM and the Bidirectional Forwarding Detection (BFD) Protocol

Understanding Bidirectional Forwarding Detection Authentication for PIM

Bidirectional Forwarding Detection (BFD) enables rapid detection of communication failures between adjacent systems. By default, authentication for BFD sessions is disabled. However, when you run BFD over Network Layer protocols, the risk of service attacks can be significant. We strongly recommend using authentication if you are running BFD over multiple hops or through insecure tunnels.

Beginning with Junos OS Release 9.6, Junos OS supports authentication for BFD sessions running over PIM. BFD authentication is only supported in the Canada and United States version of the Junos OS image and is not available in the export version.

You authenticate BFD sessions by specifying an authentication algorithm and keychain, and then associating that configuration information with a security authentication keychain using the keychain name.

The following sections describe the supported authentication algorithms, security keychains, and level of authentication that can be configured:

BFD Authentication Algorithms

Junos OS supports the following algorithms for BFD authentication:

  • simple-password—Plain-text password. One to 16 bytes of plain text are used to authenticate the BFD session. One or more passwords can be configured. This method is the least secure and should be used only when BFD sessions are not subject to packet interception.

  • keyed-md5—Keyed Message Digest 5 hash algorithm for sessions with transmit and receive intervals greater than 100 ms. To authenticate the BFD session, keyed MD5 uses one or more secret keys (generated by the algorithm) and a sequence number that is updated periodically. With this method, packets are accepted at the receiving end of the session if one of the keys matches and the sequence number is greater than or equal to the last sequence number received. Although more secure than a simple password, this method is vulnerable to replay attacks. Increasing the rate at which the sequence number is updated can reduce this risk.

  • meticulous-keyed-md5—Meticulous keyed Message Digest 5 hash algorithm. This method works in the same manner as keyed MD5, but the sequence number is updated with every packet. Although more secure than keyed MD5 and simple passwords, this method might take additional time to authenticate the session.

  • keyed-sha-1—Keyed Secure Hash Algorithm I for sessions with transmit and receive intervals greater than 100 ms. To authenticate the BFD session, keyed SHA uses one or more secret keys (generated by the algorithm) and a sequence number that is updated periodically. The key is not carried within the packets. With this method, packets are accepted at the receiving end of the session if one of the keys matches and the sequence number is greater than the last sequence number received.

  • meticulous-keyed-sha-1—Meticulous keyed Secure Hash Algorithm I. This method works in the same manner as keyed SHA, but the sequence number is updated with every packet. Although more secure than keyed SHA and simple passwords, this method might take additional time to authenticate the session.

Note:

Nonstop active routing (NSR) is not supported with meticulous-keyed-md5 and meticulous-keyed-sha-1 authentication algorithms. BFD sessions using these algorithms might go down after a switchover.

Security Authentication Keychains

The security authentication keychain defines the authentication attributes used for authentication key updates. When the security authentication keychain is configured and associated with a protocol through the keychain name, authentication key updates can occur without interrupting routing and signaling protocols.

The authentication keychain contains one or more keychains. Each keychain contains one or more keys. Each key holds the secret data and the time at which the key becomes valid. The algorithm and keychain must be configured on both ends of the BFD session, and they must match. Any mismatch in configuration prevents the BFD session from being created.

BFD allows multiple clients per session, and each client can have its own keychain and algorithm defined. To avoid confusion, we recommend specifying only one security authentication keychain.

Note:

Security Authentication Keychain is not supported on SRX Series devices.

Strict Versus Loose Authentication

By default, strict authentication is enabled, and authentication is checked at both ends of each BFD session. Optionally, to smooth migration from nonauthenticated sessions to authenticated sessions, you can configure loose checking. When loose checking is configured, packets are accepted without authentication being checked at each end of the session. This feature is intended for transitional periods only.

Configuring BFD for PIM

The Bidirectional Forwarding Detection (BFD) Protocol is a simple hello mechanism that detects failures in a network. BFD works with a wide variety of network environments and topologies. A pair of routing devices exchanges BFD packets. Hello packets are sent at a specified, regular interval. A neighbor failure is detected when the routing device stops receiving a reply after a specified interval. The BFD failure detection timers have shorter time limits than the Protocol Independent Multicast (PIM) hello hold time, so they provide faster detection.

The BFD failure detection timers are adaptive and can be adjusted to be faster or slower. The lower the BFD failure detection timer value, the faster the failure detection and vice versa. For example, the timers can adapt to a higher value if the adjacency fails (that is, the timer detects failures more slowly). Or a neighbor can negotiate a higher value for a timer than the configured value. The timers adapt to a higher value when a BFD session flap occurs more than three times in a span of 15 seconds. A back-off algorithm increases the receive (Rx) interval by two if the local BFD instance is the reason for the session flap. The transmission (Tx) interval is increased by two if the remote BFD instance is the reason for the session flap. You can use the clear bfd adaptation command to return BFD interval timers to their configured values. The clear bfd adaptation command is hitless, meaning that the command does not affect traffic flow on the routing device.

You must specify the minimum transmit and minimum receive intervals to enable BFD on PIM.

To enable failure detection:

  1. Configure the interface globally or in a routing instance.

    This example shows the global configuration.

  2. Configure the minimum transmit interval.

    This is the minimum interval after which the routing device transmits hello packets to a neighbor with which it has established a BFD session. Specifying an interval smaller than 300 ms can cause undesired BFD flapping.

  3. Configure the minimum interval after which the routing device expects to receive a reply from a neighbor with which it has established a BFD session.

    Specifying an interval smaller than 300 ms can cause undesired BFD flapping.

  4. (Optional) Configure other BFD settings.

    As an alternative to setting the receive and transmit intervals separately, configure one interval for both.

  5. Configure the threshold for the adaptation of the BFD session detection time.

    When the detection time adapts to a value equal to or greater than the threshold, a single trap and a single system log message are sent.

  6. Configure the number of hello packets not received by a neighbor that causes the originating interface to be declared down.
  7. Configure the BFD version.
  8. Specify that BFD sessions should not adapt to changing network conditions.

    We recommend that you not disable BFD adaptation unless it is preferable not to have BFD adaptation enabled in your network.

  9. Verify the configuration by checking the output of the show bfd session command.

Configuring BFD Authentication for PIM

  1. Specify the BFD authentication algorithm for the PIM protocol.

  2. Associate the authentication keychain with the PIM protocol.

  3. Configure the related security authentication keychain.

Beginning with Junos OS Release 9.6, you can configure authentication for Bidirectional Forwarding Detection (BFD) sessions running over Protocol Independent Multicast (PIM). Routing instances are also supported.

The following sections provide instructions for configuring and viewing BFD authentication on PIM:

Configuring BFD Authentication Parameters

BFD authentication is only supported in the Canada and United States version of the Junos OS image and is not available in the export version.

To configure BFD authentication:

  1. Specify the algorithm (keyed-md5, keyed-sha-1, meticulous-keyed-md5, meticulous-keyed-sha-1, or simple-password) to use for BFD authentication on a PIM route or routing instance.
    Note:

    Nonstop active routing (NSR) is not supported with the meticulous-keyed-md5 and meticulous-keyed-sha-1 authentication algorithms. BFD sessions using these algorithms might go down after a switchover.

  2. Specify the keychain to be used to associate BFD sessions on the specified PIM route or routing instance with the unique security authentication keychain attributes.

    The keychain you specify must match the keychain name configured at the [edit security authentication key-chains] hierarchy level.

    Note:

    The algorithm and keychain must be configured on both ends of the BFD session, and they must match. Any mismatch in configuration prevents the BFD session from being created.

  3. Specify the unique security authentication information for BFD sessions:
    • The matching keychain name as specified in Step 2.

    • At least one key, a unique integer between 0 and 63. Creating multiple keys allows multiple clients to use the BFD session.

    • The secret data used to allow access to the session.

    • The time at which the authentication key becomes active, in the format yyyy-mm-dd.hh:mm:ss.

    Note:

    Security Authentication Keychain is not supported on SRX Series devices.

  4. (Optional) Specify loose authentication checking if you are transitioning from nonauthenticated sessions to authenticated sessions.
  5. (Optional) View your configuration by using the show bfd session detail or show bfd session extensive command.
  6. Repeat these steps to configure the other end of the BFD session.

Viewing Authentication Information for BFD Sessions

You can view the existing BFD authentication configuration by using the show bfd session detail and show bfd session extensive commands.

The following example shows BFD authentication configured for the ge-0/1/5 interface. It specifies the keyed SHA-1 authentication algorithm and a keychain name of bfd-pim. The authentication keychain is configured with two keys. Key 1 contains the secret data “$ABC123/” and a start time of June 1, 2009, at 9:46:02 AM PST. Key 2 contains the secret data “$ABC123/” and a start time of June 1, 2009, at 3:29:20 PM PST.

If you commit these updates to your configuration, you see output similar to the following example. In the output for the show bfd session detail command, Authenticate is displayed to indicate that BFD authentication is configured. For more information about the configuration, use the show bfd session extensive command. The output for this command provides the keychain name, the authentication algorithm and mode for each client in the session, and the overall BFD authentication configuration status, keychain name, and authentication algorithm and mode.

show bfd session detail

show bfd session extensive

Example: Configuring BFD Liveness Detection for PIM IPv6

This example shows how to configure Bidirectional Forwarding Detection (BFD) liveness detection for IPv6 interfaces configured for the Protocol Independent Multicast (PIM) topology. BFD is a simple hello mechanism that detects failures in a network.

The following steps are needed to configure BFD liveness detection:

  1. Configure the interface.

  2. Configure the related security authentication keychain.

  3. Specify the BFD authentication algorithm for the PIM protocol.

  4. Configure PIM, associating the authentication keychain with the desired protocol.

  5. Configure BFD authentication for the routing instance.

Note:

You must perform these steps on both ends of the BFD session.

Requirements

This example uses the following hardware and software components:

  • Two peer routers.

  • Junos OS 12.2 or later.

Overview

In this example. Device R1 and Device R2 are peers. Each router runs PIM, connected over a common medium.

Topology

Figure 1 shows the topology used in this example.

Figure 1: BFD Liveness Detection for PIM IPv6 TopologyBFD Liveness Detection for PIM IPv6 Topology

Assume that the routers initialize. No BFD session is yet established. For each router, PIM informs the BFD process to monitor the IPv6 address of the neighbor that is configured in the routing protocol. Addresses are not learned dynamically and must be configured.

Configure the IPv6 address and BFD liveness detection at the [edit protocols pim] hierarchy level for each router.

Configure BFD liveness detection for the routing instance at the [edit routing-instancesinstance-name protocols pim interface all family inet6] hierarchy level (here, the instance-name is instance1:

You will also configure the authentication algorithm and authentication keychain values for BFD.

In a BFD-configured network, when a client launches a BFD session with a peer, BFD begins sending slow, periodic BFD control packets that contain the interval values that you specified when you configured the BFD peers. This is known as the initialization state. BFD does not generate any up or down notifications in this state. When another BFD interface acknowledges the BFD control packets, the session moves into an up state and begins to more rapidly send periodic control packets. If a data path failure occurs and BFD does not receive a control packet within the configured amount of time, the data path is declared down and BFD notifies the BFD client. The BFD client can then perform the necessary actions to reroute traffic. This process can be different for different BFD clients.

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.

Device R1

Device R2

Procedure

Step-by-Step Procedure

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 in the Junos OS CLI User Guide.

To configure BFD liveness detection for PIM IPv6 interfaces on Device R1:

Note:

This procedure is for Device R1. Repeat this procedure for Device R2, after modifying the appropriate interface names, addresses, and any other parameters.

  1. Configure the interface, using the inet6 statement to specify that this is an IPv6 address.

  2. Specify the BFD authentication algorithm and keychain for the PIM protocol.

    The keychain is used to associate BFD sessions on the specified PIM route or routing instance with the unique security authentication keychain attributes. This keychain name should match the keychain name configured at the [edit security authentication] hierarchy level.

    Note:

    The algorithm and keychain must be configured on both ends of the BFD session, and they must match. Any mismatch in configuration prevents the BFD session from being created.

  3. Configure a routing instance (here, instance1), specifying BFD authentication and associating the security authentication algorithm and keychain.

  4. Specify the unique security authentication information for BFD sessions:

    • The matching keychain name as specified in Step 2.

    • At least one key, a unique integer between 0 and 63. Creating multiple keys allows multiple clients to use the BFD session.

    • The secret data used to allow access to the session.

    • The time at which the authentication key becomes active, in the format YYYY-MM-DD.hh:mm:ss.

Results

Confirm your configuration by issuing the show interfaces, show protocols, show routing-instances, and show security commands. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

Verification

Confirm that the configuration is working properly.

Verifying the BFD Session

Purpose

Verify that BFD liveness detection is enabled.

Action
Meaning

The display from the show pim neighbors detail command shows BFD: Enabled, Operational state: Up, indicating that BFD is operating between the two PIM neighbors. For additional information about the BFD session (including the session ID number), use the show bfd session extensive command.

Release History Table
Release
Description
9.6
Beginning with Junos OS Release 9.6, Junos OS supports authentication for BFD sessions running over PIM. BFD authentication is only supported in the Canada and United States version of the Junos OS image and is not available in the export version.
9.6
Beginning with Junos OS Release 9.6, you can configure authentication for Bidirectional Forwarding Detection (BFD) sessions running over Protocol Independent Multicast (PIM). Routing instances are also supported.