> For the complete documentation index, see [llms.txt](https://docs.link11.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.link11.com/reference/bgp-community-values.md).

# BGP Community Values

The Netflow DDoS Detector service offers various parameters for rerouting traffic into Link11 for filtering, including [BGP session customization](/product-guides/netflow-ddos-detector/interface/config.md#optional-bgp-session-settings).

For this purpose, Link11 provides a range of BGP community values to enable flexible, on-demand control over route propagation, local preference, and traffic shaping. These are available to customers using our BGP-based scrubbing and mitigation services.

All communities follow the format:\
`34309:`xxxx

### Community Tags

#### 1. Local Preference Control

These communities set the local preference (local-pref) within the AS34309 network. Lower local-pref values make a route less preferred internally. Use these to influence how traffic exits our network.

| Community | Description                                          |
| --------- | ---------------------------------------------------- |
| 34309:90  | Set local-pref to 90 (less preferred than transit)   |
| 34309:130 | Set local-pref to 130 (less preferred than peering)  |
| 34309:190 | Set local-pref to 190 (less preferred than customer) |

**Use case**: Prefer one route over another within our mitigation network by influencing route selection.

***

#### 2. Blackhole Routing

| Community | Description                                                  |
| --------- | ------------------------------------------------------------ |
| 34309:666 | Blackhole traffic to the prefix (IPv4 /32 or IPv6 /128 only) |

**Use case**: Use this for targeted blackholing of IPs under active attack.

***

#### 3. AS-Path Prepending (Upstream and Exchange Specific)

These communities allow you to prepend our ASN (34309) when announcing routes to specific upstream providers or internet exchanges, influencing inbound traffic paths.\
Use x to specify the number of prepends:

* x = 1–5: Prepend AS34309 that many times.
* x = 0: Do not announce to that provider or IX.

| Community Pattern | Target                        |
| ----------------- | ----------------------------- |
| 34309:101x        | TeliaSonera (AS1299)          |
| 34309:102x        | T-Systems (AS3320)            |
| 34309:103x        | Cogent Communications (AS174) |
| 34309:104x        | Singtel (AS7473)              |
| 34309:108x        | RETN (AS9002)                 |
| 34309:111x        | DE-CIX                        |
| 34309:112x        | AMS-IX                        |
| 34309:113x        | Singapore EquinixIX           |
| 34309:114x        | LINX                          |
| 34309:115x        | Digital Realty NYC            |
| 34309:116x        | SwissIX                       |
| 34309:117x        | Any2 Los Angeles              |

Examples:

* 34309:1032 — Prepend AS34309 twice when sending to Cogent.
* 34309:1140 — Do not announce the route to LINX.

***

#### 4. Regional Route Filtering

These communities control whether prefixes are announced to transit or peering in specific geographic regions. Useful for limiting visibility during localized attacks or maintaining geographic traffic control.

| Community  | Description                            |
| ---------- | -------------------------------------- |
| 34309:1901 | Do not announce to transit in EMEA     |
| 34309:1902 | Do not announce to peering in EMEA     |
| 34309:1903 | Do not announce to transit in Americas |
| 34309:1904 | Do not announce to peering in Americas |
| 34309:1905 | Do not announce to transit in Asia     |
| 34309:1906 | Do not announce to peering in Asia     |

**Use case**: Isolate your announcements to specific regions or avoid congested upstreams during a mitigation event.

***

#### 5. AS-Path Override

These communities explicitly set or overwrite the AS path for the tagged routes within AS34309’s network. **Use with caution** — this will replace any customer-supplied AS-path attributes.

| Community  | Description                                                                      |
| ---------- | -------------------------------------------------------------------------------- |
| 34309:2920 | Force AS path to AS34309 (overrides all customer prepends or AS-path attributes) |

### How to Use

To apply one or more communities, attach them to your BGP announcements via [the Communities option in the BGP Attributes](/product-guides/netflow-ddos-detector/interface/config.md#optional-bgp-session-settings). Multiple communities can be applied per route to combine behaviors.