When TLS_FALLBACK_SCSV (Signaling Cipher Suite Value) is not supported, it can lead to potential downgrade attacks. Here are strategies to mitigate this risk:

**Proactive Strategies**

1. **Disable SSL/TLS Version Fallback**: Configure servers to disable fallback to older SSL/TLS versions. This prevents attackers from forcing connections to use vulnerable protocols.

2. **Enforce Minimum TLS Version**: Set a minimum acceptable TLS version (e.g., TLS 1.2) on both client and server sides to prevent downgrade to vulnerable versions.

3. **Regular Security Scans**: Conduct periodic scans of your infrastructure to identify and address any TLS configuration weaknesses.

4. **Monitor for Unusual TLS Negotiation Patterns**: Implement monitoring to detect attempts at forcing protocol downgrades.

**Implementation Examples**

1. Nginx Configuration

To disable SSL/TLS version fallback and enforce a minimum TLS version in Nginx:

```nginx
server {
    listen 443 ssl;
    ssl_protocols TLSv1.2 TLSv1.3;
    ssl_prefer_server_ciphers on;
    ssl_ciphers 'ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256';
    # Other SSL settings...
}
```

2. Apache Configuration

For Apache, use the following configuration to achieve similar results:

```apache
<VirtualHost *:443>
    SSLEngine on
    SSLProtocol -all +TLSv1.2 +TLSv1.3
    SSLCipherSuite ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256
    SSLHonorCipherOrder on
    # Other SSL settings...
</VirtualHost>
```

3. OpenSSL Command for Testing

Use OpenSSL to test your server's TLS configuration:

```bash
openssl s_client -connect example.com:443 -tls1_2
```

This command attempts to establish a TLS 1.2 connection. If successful, it indicates that your server is correctly configured to use modern TLS versions.

**Monitoring for Downgrade Attempts**

- Using fail2ban

You can use `fail2ban` to monitor logs for potential downgrade attempts:

1. Create a custom filter in `/etc/fail2ban/filter.d/tls-downgrade.conf`:

```ini
[Definition]
failregex = SSL routines:SSL23_GET_CLIENT_HELLO:unsupported protocol.*client=<HOST>
```

2. Add a jail in `/etc/fail2ban/jail.local`:

```ini
[tls-downgrade]
enabled = true
filter = tls-downgrade
logpath = /var/log/nginx/error.log
maxretry = 3
bantime = 3600
```

3. Restart fail2ban:

```bash
sudo systemctl restart fail2ban
```

This configuration will ban IP addresses that make repeated attempts to connect using unsupported (likely older) SSL/TLS versions.

By implementing these measures, you can significantly reduce the risk of TLS downgrade attacks, even when TLS_FALLBACK_SCSV is not supported.