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Configuring Independent Micro BFD Sessions for LAG

 

The Bidirectional Forwarding Detection (BFD) protocol is a simple detection protocol that quickly detects failures in the forwarding paths. A link aggregation group (LAG) combines multiple links between devices that are in point-to-point connections, thereby increasing bandwidth, providing reliability, and allowing load balancing. To run a BFD session on LAG interfaces, configure an independent, asynchronous mode BFD session on every LAG member link in a LAG bundle. Instead of a single BFD session monitoring the status of the UDP port, independent micro BFD sessions monitor the status of individual member links.

To enable failure detection for aggregated Ethernet interfaces:

  1. Include the following statement in the configuration at the [edit interfaces aex aggregated-ether-options] hierarchy level:
  2. Configure the authentication criteria of the BFD session for LAG.

    To specify the authentication criteria, include the authentication statement:

    • Specify the algorithm to be used to authenticate the BFD session. You can use one of the following algorithms for authentication:

      • keyed-md5

      • keyed-sha-1

      • meticulous-keyed-md5

      • meticulous-keyed-sha-1

      • simple-password

    • To configure the key chain, specify the name that is associated with the security key for the BFD session. The name you specify must match one of the key chains configured in the authentication-key-chains key-chain statement at the [edit security] hierarchy level.

    • Configure loose authentication checking on the BFD session. Use only for transitional periods when authentication might not be configured at both ends of the BFD session.

  3. Configure BFD timers for aggregated Ethernet interfaces.

    To specify the BFD timers, include the detection-time statement:

    Specify the threshold value. This is the maximum time interval for detecting a BFD neighbor. If the transmit interval is greater than this value, the device triggers a trap.

  4. Configure a hold-down interval value to set the minimum time that the BFD session must remain up before a state change notification is sent to the other members in the LAG network.

    To specify the hold-down interval, include the holddown-interval statement:

    You can configure a number in the range from 0 through 255,000 milliseconds, and the default is 0. If the BFD session goes down and then comes back up during the hold-down interval, the timer is restarted.

    This value represents the minimum interval at which the local routing device transmits BFD packets, as well as the minimum interval in which the routing device expects to receive a reply from a neighbor with which it has established a BFD session. You can configure a number in the range from 1 through 255,000 milliseconds. You can also specify the minimum transmit and receive intervals separately.

  5. Configure the source address for the BFD session.

    To specify a local address, include the local-address statement:

    The BFD local address is the loopback address of the source of the BFD session.

    Note

    Beginning with Junos OS Release 16.1, you can also configure this feature with the AE interface address as the local address in a micro BFD session. For the IPv6 address family, disable duplicate address detection before configuring this feature with the AE interface address. To disable duplicate address detection, include the dad-disable statement at the [edit interface aex unit y family inet6] hierarchy level.

    Beginning with Release 16.1R2, Junos OS checks and validates the configured micro BFD local-address against the interface or loopback IP address before the configuration commit. Junos OS performs this check on both IPv4 and IPv6 micro BFD address configurations, and if they do not match, the commit fails.

  6. Specify the minimum interval that indicates the time interval for transmitting and receiving data.

    This value represents the minimum interval at which the local routing device transmits BFD packets, as well as the minimum interval in which the routing device expects to receive a reply from a neighbor with which it has established a BFD session. You can configure a number in the range from 1 through 255,000 milliseconds. You can also specify the minimum transmit and receive intervals separately.

    To specify the minimum transmit and receive intervals for failure detection, include the minimum-interval statement:

    Note

    BFD is an intensive protocol that consumes system resources. Specifying a minimum interval for BFD less than 100 ms for Routing Engine-based sessions and 10 ms for distributed BFD sessions can cause undesired BFD flapping.

    Depending on your network environment, these additional recommendations might apply:

    • For large-scale network deployments with a large number of BFD sessions, specify a minimum interval of 300 ms for Routing Engine-based sessions and 100 ms for distributed BFD sessions.

    • For very large-scale network deployments with a large number of BFD sessions, contact Juniper Networks customer support for more information.

    • For BFD sessions to remain up during a Routing Engine switchover event when nonstop active routing is configured, specify a minimum interval of 2500 ms for Routing Engine-based sessions. For distributed BFD sessions with nonstop active routing configured, the minimum interval recommendations are unchanged and depend only on your network deployment.

  7. Specify only the minimum receive interval for failure detection by including the minimum-receive-interval statement:

    This value represents the minimum interval in which the local routing device expects to receive a reply from a neighbor with which it has established a BFD session. You can configure a number in the range from 1 through 255,000 milliseconds.

  8. Specify the number of BFD packets that were not received by the neighbor that causes the originating interface to be declared down by including the multiplier statement:

    The default value is 3. You can configure a number in the range from 1 through 255.

  9. Configure the neighbor in a BFD session.

    The neighbor address can be either an IPv4 or an IPv6 address.

    To specify the next hop of the BFD session, include the neighbor statement:

    The BFD neighbor address is the loopback address of the remote destination of the BFD session.

    Note

    Beginning with Junos OS Release 16.1, you can also configure the AE interface address of the remote destination as the BFD neighbor address in a micro BFD session.

  10. (Optional) Configure BFD sessions not to adapt to changing network conditions.

    To disable BFD adaptation, include the no-adaptation statement:

    Note

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

  11. Specify a threshold for detecting the adaptation of the detection time by including the threshold statement:

    When the BFD session detection time adapts to a value equal to or greater than the threshold, a single trap and a system log message are sent. The detection time is based on the multiplier of the minimum-interval or the minimum-receive-interval value. The threshold must be a higher value than the multiplier for either of these configured values. For example, if the minimum-receive-interval is 300 ms and the multiplier is 3, the total detection time is 900 ms. Therefore, the detection time threshold must have a value greater than 900.

  12. Specify only the minimum transmit interval for failure detection by including the transmit-interval minimum-interval statement:

    This value represents the minimum interval at which the local routing device transmits BFD packets to the neighbor with which it has established a BFD session. You can configure a value in the range from 1 through 255,000 milliseconds.

  13. Specify the transmit threshold for detecting the adaptation of the transmit interval by including the transmit-interval threshold statement:

    The threshold value must be greater than the transmit interval. When the BFD session detection time adapts to a value greater than the threshold, a single trap and a system log message are sent. The detection time is based on the multiplier of the minimum-interval or the minimum-receive-interval value. The threshold must be a higher value than the multiplier for either of these configured values.

  14. Specify the BFD version by including the version statement:

    The default is to have the version detected automatically.

Note

This feature works when both the devices support BFD. If BFD is configured at only one end of the LAG, this feature does not work.