Closed User Group Route Service Guide

DE-CIX PS Team Updated by DE-CIX PS Team

The DE-CIX Closed User Group route service (see RFC 7947 for a detailed description) facilitates the exchange of BGP announcements between peers. The route service consists of a pair of route servers for redundancy purposes. Each peer just needs to set up a BGP session per IP address family to the route servers in order to receive BGP announcements from other participating peers.

The software utilized to provide the service is BIRD. Of the two route servers, technically only one is required. However, in order to make full use of the route service, every peer is strongly encouraged to connect to both machines for redundancy purposes, so that if one machine is out of service (e.g. planned maintenance), the route service remains available.

Best Path Selection Process

Import

The route servers select the best path (best route) according to the following rules:

  1. prefer route with the highest Local Preference attribute (can be set to 0 via GRACEFUL_SHUTDOWN community, default is 100)
  2. prefer route with the shortest AS path
  3. route origin: IGP (i) > EGP (e) > incomplete (?)
  4. prefer the lowest value of the MED (Multiple Exit Discriminator)
    MED is only compared between the same peer ASN (e.g. if you're announcing the same route(s) from ≥ 2 routers)
  5. prefer the oldest known route (implies higher stability)

Each route is evaluated against the rules from top to bottom until a tie breaker is found.

Export

If an export filter is preventing the export of a previously selected best path route (e.g. due to traffic engineering via Action BGP Communities) the second best route (if available) is exported. If the second best route is also rejected on export, the third best route will be exported and so on.

Route Server Control

The route server can be controlled with BGP Communities.

Route Redistribution

Evaluation Order

Action

BGP Community (RFC 1997) 

BGP Large Community (RFC 8092)

1

Do not redistribute to <PEER ASN>

0:<PEER ASN>

<RS ASN>:0:<PEER ASN>

2

Redistribute to <PEER ASN>

<RS ASN>:<PEER ASN>

65534:<PEER ASN> for route servers with 4B ASN

<RS ASN>:1:<PEER ASN>

3

Do not redistribute

0:<RS ASN>

0:65534 for route servers with 4B ASN

<RS ASN>:0:0

4

Redistribute to all (default)

<RS ASN>:<RS ASN>

65534:65534 for RS with 4B ASN

<RS ASN>:1:0

AS Path Prepending

Prepend once

65001:0

<RS ASN>:101:0

Prepend twice

65002:0

<RS ASN>:102:0

Prepend three times

65003:0

<RS ASN>:103:0

Prepend once selective

65001:<PEER ASN>

<RS ASN>:101:<PEER ASN>

Prepend twice selective

65002:<PEER ASN>

<RS ASN>:102:<PEER ASN>

Prepend three times selective

65003:<PEER ASN>

<RS ASN>:103:<PEER ASN>

Misc

GRACEFUL_SHUTDOWN

65535:0

Set BGP local preference to 0

Route Server Route Tagging

The route server will mark all routes with four BGP Large Communities to indicate their origin.

  • Switch: Indicates at which switch a route has been injected into the DE-CIX platform. We tag the corresponding edge switch.
    • Example: edge03.fra12 (<RS ASN>:1911:172)
  • Metro: The metropolitan region corresponding to the switch.
    • Example: Frankfurt (<RS ASN>:1912:0)
  • Country: The country corresponding to the above (UN M49 format).
    • Example: Germany (<RS ASN>:1913:276)
  • Continent: The continent corresponding to the above (UN M49 format).
    • Example: Europe (<RS ASN>:1914:150)

Please have a look at this document for a comprehensive list (the communities are equal to the ones used at the GlobePEER service)

How did we do?

Overview Closed User Groups

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