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
See PTX Series PIC/FPC Compatibility for a list of PICs that are supported on each PTX Series FPC.
Micro-BFD configuration with interface addresses is not supported on PTX routers on FPC3 and QFX10000 line of switches.
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.
Starting with Junos OS Release 13.3, 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.
In Junos OS, MicroBFD control packets are always untagged by default. For L2 aggregated interfaces, the configuration must include vlan-tagging or flexible-vlan-tagging in the Aggregated Ethernet with BFD. Otherwise, the system will throw error while committing the configuration.
When you enable MicroBFD on an aggregated Ethernet Interface, the aggregated Interface can receive MicroBFD packets. Starting with Junos OS Release 19.3 and later, for MPC10E and MPC11E MPCs, you cannot apply firewall filters on the MicroBFD packets received on the aggregated Ethernet Interface. For MPC1E through MPC9E, you can apply firewall filters on the MicroBFD packets received on the aggregated Ethernet Interface only if the aggregated Ethernet Interface is configured as an untagged Interface.
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.
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.
Starting with Junos OS Release 14.1, 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 aggregated Ethernet interface address of the remote destination as the neighbor address.
Deactivate bfd-liveness-detection at the [edit interfaces aex aggregated-ether-options] hierarchy level or deactivate the aggregated Ethernet interface before changing the neighbor address from loopback IP address to aggregated Ethernet interface IP address. Modifying the local and neighbor address without deactivating bfd-liveness-detection or the aggregated Ethernet interface first might cause micro BFD sessions failure.
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.
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.