# BFD – Bidirectional Forwarding Detection

## What is BFD?

BFD stands for Bidirectional Forwarding Detection and it’s a protocol that is used for rapid detection of link failures when the line-protocol is still “up”. BFD is enabled on interface and creates a BFD session with the neighboring router (BFD Peer). Routing protocols such as EIGRP, OSPF and BGP support BFD and can rapidly detect a link failure without waiting for hold-timers to expire.

## Enabling BFD

To enable BFD per interface, use:

```
R(config)# interface INTERFACE
R(config-if)# bfd interval TX-MSEC min_rx RX-MSEC multiplier COUNT
! TX-MSEC = rate at which BFD packets are sent
! RX-MSEC = Min rate at which BFD packets are expected
! COUNT = how many packets can be missed before considering the link down
```

To verify BFD, use:

```
R# show bfd neighbors [detail]
```

## BFD Support for routing protocols

### EIGRP

To enable BFD support for EIGRP, use:

```
R(config)# router eigrp AS-NUMBER
R(config-router)# bfd {interface INTERFACE|all-interfaces}
```

To verify, use:

```
R# show ip eigrp interfaces ... [details] 
```

### OSPF

To enable BFD support for OSPF, there are 2 options:\
Option 1 is to enable OSPF support for BFD, one-by-one on each interface:

```
R(config)# interface INTERFACE
R(config-if)# ip ospf bfd
```

Option 2 is to enable OSPF support for all BFD interfaces and the disable it on unneeded interfaces:

```
R(config)# router ospf PROC-ID
R(config-router)# bfd all-interfaces
! Will enable BFD support for all interfaces
```

You can disable then OSPF support for BFD, per-interface, with:

```
R(config-if)# ip ospf bfd disable
```

To verify, use:

```
R# show ip ospf [details]
```

#### 2.3BGP

To enable BFD support for BGP, use:

```
R(config)# router bgp AS-NUMBER
R(config-router)# neighbor NEIGH-IP fall-over bfd
```

To verify, use:

```
R# show ip bgp neighbors
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://ccie.nyquist.eu/ipv4/ipv4-addressing/bfd-bidirectional-forwarding-detection.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.