# Test Summary: BFD Admin Down No Impact

## Overview

This topotest verifies the BFD Admin Down state management feature where protocol
sessions (BGP, OSPF, PIM) should NOT be torn down when BFD receives an Admin Down
notification from the peer.

## What This Test Does

### 1. Test Setup
- Creates a 2-router topology (r1 and r2)
- Configures BGP (eBGP between AS 65001 and AS 65002)
- Configures OSPF on the shared link
- Configures PIM on both routers
- Enables BFD for all protocols

### 2. Initial Convergence Test
- Waits for BGP to reach Established state
- Waits for OSPF neighbors to reach Full state
- Waits for PIM neighbors to be discovered
- Verifies BFD sessions come UP

### 3. Main Test: Admin Down Handling
**Action**: Shutdown BFD peer on r1 (using `shutdown` command in BFD peer config)

**What happens internally**:
- r1 sends BFD Admin Down to r2
- r2's BFD code detects Admin Down from peer (in `bs_up_handler()` or `bs_init_handler()`)
- r2 calls `ptm_bfd_sess_dn(bs, BD_NEIGHBOR_DOWN, true)` with `notify_admin_down=true`
- BFD transitions to DOWN state locally
- BFD notifies clients with `PTM_BFD_ADM_DOWN` instead of `PTM_BFD_DOWN`

**Protocol client behavior** (with your changes):
- **BGP** (`bgp_bfd.c`): Detects `BSS_ADMIN_DOWN`, logs event, returns without tearing down session
- **OSPF** (`ospf_bfd.c`): Detects `BSS_ADMIN_DOWN`, logs event, returns without tearing down adjacency
- **PIM** (`pim_bfd.c`): Detects `BSS_ADMIN_DOWN`, logs event, returns without deleting neighbor

**Test verifies**:
- BFD state goes to DOWN on r2
- BGP session remains Established on r2
- OSPF neighbor remains Full on r2
- PIM neighbor remains present on r2

### 4. Re-enable Test
- Re-enables BFD on r1 using `no shutdown`
- Verifies BFD session comes back UP

## How to Run the Test

### Prerequisites
You need to have built and installed FRR with your changes:

```bash
# Make sure you've compiled FRR with your changes
cd /home/sougatab/work/frr/sougatahitcs/frr
./bootstrap.sh
./configure --enable-dev-build
make
sudo make install
```

### Running the Test

```bash
# Navigate to the test directory
cd /home/sougatab/work/frr/sougatahitcs/frr/tests/topotests/bfd_admin_down_no_impact

# Run with pytest
sudo -E pytest test_bfd_admin_down_no_impact.py -s -vv

# Or run specific test functions
sudo -E pytest test_bfd_admin_down_no_impact.py::test_bfd_admin_down_no_protocol_impact -s -vv
```

### Expected Output

All tests should pass:
```
test_bfd_admin_down_no_impact.py::test_wait_protocols_convergence PASSED
test_bfd_admin_down_no_impact.py::test_bfd_peers_up PASSED
test_bfd_admin_down_no_impact.py::test_bfd_admin_down_no_protocol_impact PASSED  <-- Main test
test_bfd_admin_down_no_impact.py::test_bfd_reenable PASSED
test_bfd_admin_down_no_impact.py::test_memory_leak PASSED
```

## Alternative Ways to Trigger Admin Down

While the test uses `shutdown` in BFD peer configuration, you can also trigger
Admin Down by:

1. **Shutting down BFD profile** (if using profiles):
   ```
   configure terminal
   bfd
    profile myprofile
     shutdown
   ```

2. **Administratively shutting down the interface** (sends Admin Down before interface goes down):
   ```
   configure terminal
   interface r1-eth0
    shutdown
   ```

3. **Using BFD peer shutdown command** (as used in the test):
   ```
   configure terminal
   bfd
    peer 10.0.1.2 interface r1-eth0
     shutdown
   ```

## Debugging

If the test fails, you can debug by:

1. **Checking BFD state**:
   ```
   show bfd peers
   show bfd peers json
   ```

2. **Checking protocol states**:
   ```
   show ip bgp summary
   show ip ospf neighbor
   show ip pim neighbor
   ```

3. **Enabling debug logs**:
   ```
   debug bfd peer
   debug bfd network
   debug bgp bfd
   debug ospf bfd
   debug pim bfd
   ```

4. **Checking logs in test output**: The test runs with `-s -vv` flags which show detailed output

## Files Modified for This Feature

- `bfdd/bfd.c`: Added `notify_admin_down` parameter to `ptm_bfd_sess_dn()`
- `bfdd/bfd.h`: Updated function signature
- `bgpd/bgp_bfd.c`: Added Admin Down handling
- `ospfd/ospf_bfd.c`: Added Admin Down handling
- `ospf6d/ospf6_bfd.c`: Added Admin Down handling
- `pimd/pim_bfd.c`: Added Admin Down handling

## Test Coverage

This test covers:
- ✅ BFD Admin Down state handling
- ✅ BGP session persistence on Admin Down
- ✅ OSPF adjacency persistence on Admin Down
- ✅ PIM neighbor persistence on Admin Down
- ✅ BFD session recovery after re-enable

## Future Enhancements

Potential additions to this test:
1. Add OSPFv6 testing (currently only OSPFv2)
2. Test with BFD profiles (shutdown profile)
3. Test with multihop BFD
4. Test with BFD in VRF
5. Add negative test (ensure normal BFD DOWN still tears down sessions)


