Routing Policies – Knowledgebase

General

• Prefixes with RPKI validation-state invalid are dropped (exceptions are RTBH prefixes).
• Only prefix lengths between /8 and /24 for IPv4 and /19 and /48 for IPv6 are accepted (exceptions are RTBH prefixes).
• Bogon prefixes and Bogon ASNs are rejected on ingress.
• Strict prefix filtering based on IRR data is applied on all BGP sessions.
• Maximum accepted AS-Path length is 50.
• “Tier-1” ASNs in the as-paths from downstreams and peers are rejected.
• The first ASN (left most) in the AS-Path must equal the peer ASN.
• Peering sessions are protected with maximum prefix limits
• Inter.link does not use route-dampening.
• The Multi-exit Discriminator (MED) set by customers is honored. If unset the lowest (best) value 0 is used.
• Setting local preference via BGP communities is not supported (except GRACEFUL_SHUTDOWN), please use MED and/or AS-Path prepending for traffic-engineering.
• Prefix filters are updated once a day every (european) night.

BGP Origin Communities

Learned BGP routes are tagged at ingress with origin communities. These have informational value and indicate where a prefix was learned and from whom. The corresponding IDs are listed in the Appendix shown below.

Examples

The community combination 5405:3 5405:15 5405:208 5405:3003 5405:4004 attached to a route tells the following about the origin:

BGP Signalling Communities

BGP Large Communities can be used to control the behaviour of the routing service. Multiple of them can be attached to a single BGP announcement. They are stripped upon annuncement to other peers.

Path prepending communities

Restrict Propagation

Well-known communities

The following well-known communities are honoured.

Remote Triggered Blackholing (RTBH)

We support Remote Triggered Blackholing (RTBH) announcements that can activate across our global backbone, or more specific regions of it, depending on the attached community. See below for examples for choosing the right region. RTBH announcements are discarded if the prefix isn’t covered by the prefix filters configured for the peer announcing the route.

The accepted IDs for R,CC,ZZZ can be found in the Appendix below.

If the scope of the selective blackholing matches the only origin of the route, a global blackhole is the result.

Maximum prefix length for RTBH routes is restricted to /24 for IPv4 and /48 for IPv6. Routes with the well-known community 65535:666 are propagated to other peer/upstream ASNs as well.

For peers supporting the BLACKHOLE community, different blackhole route prefix lengths might lead to different results:

• Announcements carrying Hostroutes (IPv4 /32 and IPv6 /128) are usually accepted and the traffic is dropped in the peer network.
• Announcements carrying IPv4 prefixes with a length between /24 and /32 or IPv6 prefixes with a length between /48 and /128 might be accepted or rejected depending on the peer’s routing policy.

Examples

Appendix

Continent IDs