[L3sm] [l3sm] #21 (draft-ltsd-l3sm-l3vpn-service-model): Site-Network-Access bandwidth configuration inheritance challenge

["l3sm issue tracker" <[e-mail]>]

#21: Site-Network-Access bandwidth configuration inheritance challenge

 Section 5.2.1 titled “Site network accesses” stipulates the following:

  “Some parameters from the site can be configured also at the site-
  network-access level like : routing, services, security ... Defining
  parameters only at site level will provide inheritance. If a
  parameter is configured at both site and access level, the access
  level parameter MUST override the site level parameter”

 While this inheritance principle can be  desirable for some types of
 configuration branches (such as security), it can become problematic for
 configuration parameters such as bandwidth where the properties can be
 cumulative across multiple accesses.

 For instance, not specifying bandwidth of a new site network accesses
 would result in the inheritance principle replicating site level bandwidth
 specifications for it. This is fine as long as there is only one site
 network access but it creates ambiguity when there are several ones. In
 load sharing configurations replicating the site bandwidth specifications
 like this would acts as a bandwidth multiplier and overturn the likely
 intent of whoever specified the site bandwidth in the first place. There
 are also Primary/backup arrangement for which the Primary network access
 may be capable of handling the full bandwidth specified for the site but
 for which the backup access is only capable of a fraction of this
 performance. In all cases, this renders the site network access level
 override for bandwidth mandatory and the site level bandwidth
 specifications misleading at best.

 In a nut shell site to network access inheritance will hardly ever be
 applicable in multi-access configurations and brings little additional
 value in single access configurations. Recommendation would be to
 deprecate site level bandwidth configuration branch and set expectation
 that management system will be responsible to control explicitly what
 bandwidth parameter should be enacted for each site network accesses
 individually and in consideration of the chosen primary/backup or load
 sharing/balancing scheme.

 This is a minor point since the capability to override site level settings
 at the network access level is already present in the model but
 deprecation of site level bandwidth specification is still recommended
 because of the ambiguity (confusion) it will generate in multi network
 access configurations.

-- 
-------------------------------------+-------------------------------------
 Reporter:  [e-mail]         |      Owner:  draft-ltsd-l3sm-l3vpn-
     Type:  defect                   |  [e-mail]
 Priority:  minor                    |     Status:  new
Component:  draft-ltsd-l3sm-l3vpn-   |  Milestone:
  service-model                      |    Version:
 Severity:  -                        |   Keywords:
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Ticket URL: <https://trac.tools.ietf.org/wg/l3sm/trac/ticket/21>
l3sm <https://tools.ietf.org/l3sm/>