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    Understanding Independent Micro BFD Sessions for LAG

    Starting with Junos OS Release 13.3, this feature is supported on the following PIC/FPC types:

    • PC-1XGE-XENPAK (Type 3 FPC)
    • PD-4XGE-XFP (Type 4 FPC)
    • PD-5-10XGE-SFPP (Type 4 FPC)
    • 24x10GE (LAN/WAN) SFPP, 12x10GE (LAN/WAN) SFPP, 1x100GE Type 5 PICs
    • All MPCs on MX Series with Ethernet MICs
    • FPC-PTX-P1-A on PTX5000 with 10-Gigabit Ethernet interfaces
    • FPC2-PTX-P1A on PTX5000 with 10-Gigabit Ethernet interfaces in Junos OS Release 14.1 and later
    • All FPCs on PTX Series with Ethernet interfaces in Junos OS Release 14.1R3 and later 14.1 releases, and Junos 14.2 and later

    Tip: See PTX Series PIC/FPC Compatibility for a list of PICs that are supported on each PTX Series FPC.

    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.

    The individual BFD sessions determine the Layer 2 and Layer 3 connectivity of each member link in the LAG. Once a BFD session is established on a particular link, the member links are attached to the LAG and the load balancer either by a static configuration or by the Link Aggregation Control Protocol (LACP). If the member links are attached to the LAG by a static configuration, the device control process acts as the client to the micro BFD session. When member links are attached to the LAG by the LACP, the LACP acts as the client to the micro BFD session.

    When the micro BFD session is up, a LAG link is established and data is transmitted over that LAG link. If the micro BFD session on a member link is down, that particular member link is removed from the load balancer, and the LAG managers stop directing traffic to that link. These micro BFD sessions are independent of each other despite having a single client that manages the LAG interface.

    Note: IANA has allocated 01-00-5E-90-00-01 as the dedicated MAC address for micro BFD. Dedicated MAC mode is used by default for micro BFD sessions, in accordance with the latest draft for BFD over LAG.

    Micro BFD sessions run in the following modes:

    • Distribution Mode—Micro BFD sessions are distributed by default at Layer 3.
    • Non-Distribution Mode—You can configure the BFD session to run in this mode by including the no-delegate-processing statement under periodic packet management (PPM). In this mode, the packets are being sent or received by the Routing Engine at Layer 2.

    A pair of routing devices in a LAG exchange BFD packets at a specified, regular interval. The routing device detects a neighbor failure when it stops receiving a reply after a specified interval. This allows the quick verification of member link connectivity with or without LACP. A UDP port distinguishes BFD over LAG packets from BFD over single-hop IP.

    Note: IANA has allocated 6784 as the UDP destination port for micro BFD.

    To enable failure detection for LAG networks for aggregated Ethernet interfaces:

    • Include the bfd-liveness-detection statement in the configuration.
    • Specify 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.
    • Specify the minimum interval that indicates the time interval for transmitting and receiving data.
    • Specify the neighbor in a BFD session. In releases prior to Junos OS Release 16.1, you must configure the loopback address of the remote destination as the neighbor address. Beginning with Junos OS Release 16.1, you can also configure this feature with the AE interface address of the remote destination as the neighbor address.

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

    For the IPv6 address family, disable duplicate address detection before configuring this feature with AE interface addresses. To disable duplicate address detection, include the dad-disable statement at the [edit interface aex unit y family inet6] hierarchy level.

    Modified: 2016-05-26