CubePath Networks - BGP Communities Reference

This document describes the BGP communities supported by CubePath Networks (AS26141). Customers can attach these communities to prefixes announced to us in order to control how their routes are exported, prepended, and handled across our network.

Table of Contents

• How It Works
• Network Locations
• Local Preference Control
• Blackhole / RTBH
• DDoS Scrubbing
• No-Export Control
• Selective Export Override
• AS-Path Prepending
• MED Handling
• Examples

How It Works

When you announce a prefix to CubePath, you can attach standard BGP communities in the format 26141:XXXXX to control how we handle your route. Communities are processed in the following order:

1. Local preference is set based on customer action communities
2. No-export communities are evaluated to determine which providers should NOT receive your prefix
3. Selective export overrides are applied to force export despite no-export tags
4. Prepending communities are applied to influence inbound traffic patterns
5. Blackhole communities trigger RTBH if present

Customer routes always receive the highest local preference in our network (200) and are always preferred over transit, IXP, or PNI routes.

Network Locations

CubePath currently operates in the following locations:

1. Local Preference Control

These communities allow you to influence which of our routers prefer your prefix. Useful for active/backup setups when you are multi-homed to CubePath at multiple locations.

Default behavior (no community): Local preference is set to 200 on all routers.

When to use

• Active/Backup across continents: Announce your prefix from both sites. On the backup site, attach 26141:8000 so that only routers on the same continent as the backup use it; all other continents prefer the primary.
• Global backup: Attach 26141:8090 on the backup session to make it the last-resort path everywhere.

2. Blackhole / RTBH

Remote Triggered Black Hole (RTBH) allows you to instruct CubePath and its upstreams to drop all traffic destined to a specific prefix. This is used for DDoS mitigation.

Requirements:

• Blackhole announcements must be /32 (IPv4) or /128 (IPv6)
• The prefix must be covered by a less-specific prefix already announced by you
• Both communities are propagated to upstream transit providers that support RTBH

Supported upstream RTBH: Cogent (AS174), Lumen (AS3356), GTT (AS3257), NEAR IP (AS49600).

3. DDoS Scrubbing

If you are under a volumetric DDoS attack and want CubePath to route your traffic through upstream scrubbing services instead of blackholing it, use the scrubbing community.

How it works:

• By default, CubePath mitigates volumetric DDoS attacks locally without any community required.
• The 26141:112 community routes traffic through dedicated inline filters for deeper inspection and mitigation.
• Your IP remains fully reachable — only attack traffic is dropped.

Difference from blackhole:

• Blackhole (26141:666) drops all traffic to the prefix — the IP becomes unreachable.
• Scrubbing (26141:112) filters attack traffic through inline appliances and delivers legitimate traffic — the IP remains reachable.

Note: This community is only available for customers with the AntiDDoS Premium protection plan.

4. No-Export Control

These communities prevent CubePath from exporting your prefix to specific providers, geographies, or provider types. This gives you fine-grained control over where your routes are visible on the Internet.

Global

By Provider Type

By Specific Transit Provider

By Specific IXP

By Geographic Region

Continent level - suppress export at all sites within a continent:

Country / State level - suppress export at all sites within a country or state:

5. Selective Export Override

These communities override no-export rules. They are useful when you want to suppress export broadly (e.g., to all transits) but still allow export to a specific provider.

Selective export communities are only meaningful when combined with a no-export community. They have no effect on their own.

By Provider Type

By Specific Transit Provider

By Specific IXP

6. AS-Path Prepending

These communities instruct CubePath to prepend its own ASN (26141) to the AS-PATH when announcing your prefix to specific providers or regions. This makes the path appear longer, causing remote networks to prefer shorter paths through other providers or locations.

Global Prepending

Applied to all providers (transits and IXPs) at all sites:

Geographic Prepending - By Continent

Applied to all providers at sites within the specified continent:

Geographic Prepending - By Country / State

Applied to all providers at sites within the specified country or state:

Note: Prepend 2x and 3x variants are also available for each country/state following the same pattern (replace the last digit: 1 = 1x prepend, 2 = 2x, 3 = 3x).

Provider-Specific Prepending - Transit

Applied only when exporting to the specified transit provider:

Provider-Specific Prepending - IXP

Applied only when exporting to the specified IXP:

7. MED Handling

CubePath honors MED (Multi-Exit Discriminator) values set by customers. Your MED is never modified on inbound and is preserved throughout our network.

Use case: If you are multi-homed to CubePath at multiple sites and want fine-grained control over which site is preferred, set MED values on your announcements. Lower MED = more preferred.

Example:

Your prefix 10.0.0.0/24:
  - Announced from Miami with MED = 50  (preferred)
  - Announced from Houston with MED = 100 (backup)

Result: All CubePath routers prefer the Miami path.

Note: MED comparison only applies when comparing paths with equal local preference and AS-path length. Since all customer routes have local-pref 200, MED is the tiebreaker between multiple paths from the same customer.

8. Examples

Example 1: Announce only to Cogent

Suppress export to everyone, then selectively allow Cogent:

Communities: 26141:9000, 26141:9123

• 26141:9000 = Do not export to anyone
• 26141:9123 = Override: force export to Cogent

Result: Your prefix is only visible via Cogent (AS174).

Example 2: Announce everywhere except IXPs

Communities: 26141:40000

• 26141:40000 = Do not export to any IXP

Result: Your prefix is announced to all transits but no IXPs.

Example 3: Prefer European traffic via Amsterdam, US traffic via Houston

From your Amsterdam session, announce normally (no communities). From your Houston session, announce with:

Communities: 26141:51001

• 26141:51001 = Prepend 1x at all European sites

Result: European networks see a shorter path via Amsterdam (no prepend) and a longer path via Houston's European announcements (1x prepend). US networks see both paths without prepending.

Example 4: Backup site in Miami

From your primary site (e.g., Houston), announce normally. From Miami, announce with:

Communities: 26141:8000

• 26141:8000 = Lower local-pref beyond region

Result: All routers in North America use the Miami path normally (local-pref 200). European routers will prefer the Houston path (local-pref 200) over the Miami path (local-pref 90).

Example 5: DDoS mitigation - blackhole a /32

If you are under attack on 203.0.113.42:

Announce: 203.0.113.42/32
Communities: 26141:666

Result: CubePath and its upstream providers drop all traffic to 203.0.113.42. Remove the announcement to restore traffic.

Example 6: No-export to a specific region

Announce everywhere except from North American sites:

Communities: 26141:52000

• 26141:52000 = Do not export at North American sites

Result: Your prefix is only announced to European providers (Barcelona, Amsterdam). North American providers (Houston, Miami, Ashburn) will not receive the prefix.

Example 7: Provider-specific prepending

Make Lumen's path less preferred than other transits:

Communities: 26141:30022

• 26141:30022 = Prepend 2x to Lumen

Result: Lumen sees AS-PATH 26141 26141 26141 <your-asn>, while other transits see 26141 <your-asn>. Networks with multiple paths will prefer non-Lumen paths.

Support

For questions about BGP communities or traffic engineering, contact CubePath support at [email protected] or open a ticket via the customer portal.