RFC 7938, "Use of BGP for Routing in Large-Scale Data Centers", August 2016

Errata ID: 5477
Status: Held for Document Update
Type: Editorial
Publication Format(s) : TEXT
Reported By: Klemens Schragel
Date Reported: 2018-08-24
Held for Document Update by: Martin Vigoureux
Date Held: 2018-11-04

Section 3.2.3 says:

   The small example of topology in Figure 3 is built from devices with
   a port count of 4.  In this document, one set of directly connected
   Tier 2 and Tier 3 devices along with their attached servers will be
   referred to as a "cluster".  For example, DEV A, B, C, D, and the
   servers that connect to DEV A and B, on Figure 3 form a cluster.  The
   concept of a cluster may also be a useful concept as a single
   deployment or maintenance unit that can be operated on at a different
   frequency than the entire topology.

It should say:

   The small example of topology in Figure 3 is built from devices with
   a port count of 4. By introducing an additional Tier the 4-port
   Tier 1 device has still two unused ports to connect further devices,
   therefore scaling from a maximum of 8 servers in a 3-stage Clos to a
   maximum of 16 servers in this 5-stage Clos.
   In this document, one set of directly connected Tier 2 and Tier 3
   devices along with their attached servers will be referred to as a
   "cluster".  For example, DEV A, B, C, D, and the servers that
   connect to DEV A and B, on Figure 3 form a cluster.  The concept of
   a cluster may also be a useful concept as a single deployment or
   maintenance unit that can be operated on at a different frequency
   than the entire topology.

Notes:

Section does not properly describe where the scaling happens, also the depicted topology still connects only 8 servers (the same amount as with a 3-stage Clos). The reader can grasp the scaling only when looking very carefully at the figure.

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