Bidirectional Forwarding Detection (BFD)
This section provides information about using BFD with BGP and OSPF protocols on the Session Smart Networking Platform.
Overview
BFD asynchronous mode can be enabled on the OSPF interface or the BGP neighbor. BFD configuration allows the following BFD parameters to be set:
- enable (default: false): Enable/disable BFD asynchronous mode.
- multiplier (default: 3): The number of BFD packets that can be lost without the BFD session declared as down.
- required-min-rx-interval (default: 1000): The minimum interval in milliseconds that this system must receive a BFD control packet.
- desired-tx-interval (default: 1000): The minimum transmission interval in milliseconds used to send BFD control packets.
For OSPF, the BFD configuration can be created for the given OSPF interface. Once a neighbor is learned on this interface, then a BFD session is created with the same addresses used to create the OSPF adjacency.
For BGP, the BFD configuration is created for a BGP neighbor. Once the BGP neighbor is learned, then a BGP session is created. BFD uses the same addresses as the BGP adjacency. These can be interface addresses for directly connected BGP neighbors, or loopback addresses.
The BFD peers are automatically removed by the protocols once the BGP/OSPF neighbor is removed. The OSPF/BGP adjacency remains up when BFD is configured for the peer. However, if the BFD configuration is modified while the BFD session is Up, then the OSPF/BGP adjacency will flap.
Configuration
The following is a simple configuration for OSPF and BGP.
authority
router A
routing default-instance
ospf 2
area 0.0.0.0
interface T217_DUT2 inet20
node T217_DUT2
interface inet20
bfd
enable true
required-min-rx-interval 500
desired-tx-interval 500
multiplier 3
routing-protocol bgp
neighbor 1.0.0.11
bfd
enable true
required-min-rx-interval 500
desired-tx-interval 500
multiplier 5
BFD can also be enabled in the VRF.
authority
router A
routing default-instance
vrf vrfA
ospf 2
area 0.0.0.0
interface T217_DUT2 inet30
node T217_DUT2
interface inet30
bfd
enable true
required-min-rx-interval 500
desired-tx-interval 500
multiplier 3
routing-protocol bgp
neighbor 1.0.0.11
bfd
enable true
required-min-rx-interval 500
desired-tx-interval 500
multiplier 3
Troubleshooting
The following show commands are available through the SSR PCLI. Additionally, the BFD status is available in the GUI.
The following show commands are also available for insight into the configuration:
show bfd [vrf <name>] [peer <ip>] [<verbosity>]
Example Output
# show bfd
Tue 2022-02-01 15:31:46 UTC
======= =========== ========== ======= =============
Vrf Peer Local State Uptime
======= =========== ========== ======= =============
16.0.0.3 16.0.0.2 up 15h 54m 2s
music 11.1.20.4 g20 up 37m 29s
11.1.10.4 g10 up 15h 58m 52s
# show bfd vrf music peer 11.1.20.4
Tue 2022-02-01 15:41:16 UTC
======= =========== ======= ======= ========
Vrf Peer Local State Uptime
======= =========== ======= ======= ========
music 11.1.20.4 g20 up 19s
# show bfd detail
Tue 2022-02-01 15:39:13 UTC
==========================================
Information
==========================================
Item:
Remote Detect Multiplier: 3
Remote Receive Interval: 1000
Remote: 1167833603
Vrf: default
Id: 3654638929
Receive Interval: 1000
Remote Transmit Interval: 1000
Multihop: True
Detect Multiplier: 3
Passive Mode: False
Status: up
Remote Echo Interval: 50
Local: 16.0.0.2
Remote Diagnostic: ok
Peer: 16.0.0.3
Echo Interval: 0
Uptime: 57689
Minimum Ttl: 252
Diagnostic: ok
Transmit Interval: 1000
Item:
Remote Detect Multiplier: 3
Remote: 3892773233
Interface: g20
Remote Receive Interval: 1000
Vrf: music
Id: 927933835
Receive Interval: 1000
Remote Transmit Interval: 1000
Multihop: False
Detect Multiplier: 3
Passive Mode: False
Status: up
Remote Echo Interval: 50
Remote Diagnostic: ok
Peer: 11.1.20.4
Echo Interval: 0
Uptime: 2696
Diagnostic: ok
Transmit Interval: 1000
Item:
Remote Detect Multiplier: 3
Remote: 3305953639
Interface: g10
Remote Receive Interval: 1000
Vrf: default
Id: 1713249686
Receive Interval: 1000
Remote Transmit Interval: 1000
Multihop: False
Detect Multiplier: 3
Passive Mode: False
Status: up
Remote Echo Interval: 50
Remote Diagnostic: ok
Peer: 11.1.10.4
Echo Interval: 0
Uptime: 57979
Diagnostic: ok
Transmit Interval: 1000
BFD Echo Mode Tests
This feature enables BFD asynchronous mode support. Many routers use BFD echo mode to ensure a forwarding path is available. While the SSR does not support the sending of BFD echo mode tests to a non-SSR router, we can return the echo mode traffic to the originating router allowing it to pass its echo mode test. Unlike BFD asynchronous mode, BFD echo mode is not handled by a BFD process on the peer router. Instead, it is intended to be processed by the packet forwarding plane and returned to the originating router. In order to pass this echo test traffic, an SSR must be configured to allow this traffic just like any other forwarding traffic. This requires a tenant and a service as with all traffic forwarded by the SSR.
To verify that the SSR is capable of relaying the echo mode packets, first identify the tenant from the ingress interface and source IP address of the peer router. Then, check the FIB to verify that there is a match to a service for this tenant. BFD echo traffic typically uses UDP destination port 3785 and should have the destination IP address of the peer router. A valid configuration does not require a specific service for BFD so long as this traffic is covered by another configured service. The next-hop of the FIB entry must point towards the egress interface that connects to this peer router.