Re: [Lsr] [Technical Errata Reported] RFC2328 (5956)

[Alvaro Retana <[e-mail]>]

On January 9, 2020 at 11:13:26 AM, Acee Lindem wrote:

[Trimming the distribution list.]

Hi!

I agree with Acee, but for different reasons.

> I don't agree this change is required. The non-normative appendix C text
> clearly states that this is the "cost of sending a packet on the interface".
> The examples cited are cases where reachability to a local address is
> provided. Now, there are cases where it is useful to specify a non-zero cost
> for a loopback address (e.g., Anycast addresses) but these scenarios are out
> of scope.


I always thought that the Appendices were normative...among other
things because of how they are referenced in the text, they define the
LSA formats, etc.   But §9 (The Interface Data Structure) contains the
same text anyway:

   Interface output cost(s)
       The cost of sending a data packet on the interface, expressed in
       the link state metric.  This is advertised as the link cost for
       this interface in the router-LSA. The cost of an interface must
       be greater than zero.



Acee is right in pointing out that the text above doesn't apply
because "reachability to a local address is provided"; in fact, both
the examples mentioned say that the information is "indicating a host
route"...

§12.4.1 (Router-LSAs):

   A host route is represented as a Type 3 link (stub network)
   whose Link ID is the host's IP address, Link Data is the mask
   of all ones (0xffffffff), and cost the host's configured cost
   (see Section C.7).

...and from §C.7 (Host route parameters):

   Cost of link to host
       The cost of sending a packet to the host, in terms of the
       link state metric.  However, since the host probably has
       only a single connection to the internet, the actual
       configured cost in many cases is unimportant (i.e., will
       have no effect on routing).


The specification says that for a host route the cost doesn't matter,
so the fact that the examples indicate "cost set to 0" is not in
conflict.

Alvaro.


> On 1/8/20, 4:58 PM, "RFC Errata System" wrote:
>
> The following errata report has been submitted for RFC2328,
> "OSPF Version 2".
>
> --------------------------------------
> You may review the report below and at:
> https://www.rfc-editor.org/errata/eid5956
>
> --------------------------------------
> Type: Technical
> Reported by: Marcelo Bustani
>
> Section: 12.4.1
>
> Original Text
> -------------
> Router-LSAs
>
> If the state of the interface is Loopback, add a Type 3
> link (stub network) as long as this is not an interface
> to an unnumbered point-to-point network. The Link ID
> should be set to the IP interface address, the Link Data
> set to the mask 0xffffffff (indicating a host route),
> and the cost set to 0.
>
> ===================================
> 12.4.1.4. Describing Point-to-MultiPoint interfaces
>
> For operational Point-to-MultiPoint interfaces, one or
> more link descriptions are added to the router-LSA as
> follows:
>
> o A single Type 3 link (stub network) is added with
> Link ID set to the router's own IP interface
> address, Link Data set to the mask 0xffffffff
> (indicating a host route), and cost set to 0.
> =============================================================================
> C.3 Router interface parameters
>
> Interface output cost
> The cost of sending a packet on the interface, expressed in
> the link state metric. This is advertised as the link cost
> for this interface in the router's router-LSA. The interface
> output cost must always be greater than 0.
>
>
> Corrected Text
> --------------
> "cost set to 0" to at least "greater than 0"
>
> Notes
> -----
> The section 12.4.1 and 12.4.1.4 are inconsistent with the appendix c.3.
>
> These both section we find the cost to stub networks have to be set to 0, but
> in appendix c.3 we see that the interfaces must have greater than 0.
>
> Instructions:
> -------------
> This erratum is currently posted as "Reported". If necessary, please
> use "Reply All" to discuss whether it should be verified or
> rejected. When a decision is reached, the verifying party
> can log in to change the status and edit the report, if necessary.
>
> --------------------------------------
> RFC2328 (no draft string recorded)
> --------------------------------------
> Title : OSPF Version 2
> Publication Date : April 1998
> Author(s) : J. Moy
> Category : INTERNET STANDARD
> Source : Open Shortest Path First IGP
> Area : Routing
> Stream : IETF
> Verifying Party : IESG