Re: [Teas] Benjamin Kaduk's No Objection on draft-ietf-teas-sr-rsvp-coexistence-rec-03: (with COMMENT)

[Harish Sitaraman <[e-mail]>]

Hi Benjamin,

Thanks for your comments. See inline [HS]...

On 5/9/18, 11:29 AM, "Benjamin Kaduk" <[e-mail]> wrote:

    Benjamin Kaduk has entered the following ballot position for
    draft-ietf-teas-sr-rsvp-coexistence-rec-03: No Objection
    
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    COMMENT:
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    TED/its expansion should be introduced in the Introduction, not the
    Abstract, since the Abstract and the rest of the document must be
    able to be read in a standalone manner.

[HS] Ok - we can retain " traffic engineering database" and remove "(TED)" in the abstract and move it to the Introduction.
    
    In line with Alvaro's comment, I would suggest moving Sections 3.1
    through 3.4 into a new parent section "Discarded Options" or
    similarly-named.
    
[HS] The solutions are not discarded and it is left to the operator's choice even though a solution may not satisfy all the requirements. 
        I had responded to Alvaro's comment and proposed adding some text in section 3 (before 3.1) to clarify this.
    
    Section 3.5
    
       [...] It is RECOMMENDED that the IGP-TE update
       threshold SHOULD be lower in order to flood unreserved bandwidth
       updates often.
    
    Lower than what?
    
[HS] Vendors may offer the ability for the operator to decide how often (as a %/value of change) to flood changes to available bandwidth and unreserved bandwidth for a TE link. As part of Alvaro's comments, we are removing RECOMMENDED. We could further change the above to "The IGP-TE update threshold SHOULD allow for more frequent flooding of unreserved bandwidth".
    
    Section 7
    
    It feels odd to say that these "do not require any new security
    considerations" and then go and list some new security
    considerations.  I would suggest something like "The security
    considerations of each protocol are unaffected by the presence of
    the other, so only the interactions of the TED consistency solution
    with the individual protocols needs to be considered."
    
    I would probably also want to expand the text a bit, noting that:
    
    A hijacked SR traffic stream could potentially cause disruption to
    RSVP-TE LSPs in two ways: directly, but consuming sufficient
    bandwidth to cause traffic loss, and indirectly, by consuming
    sufficient traffic to result in the TED consistency solution
    proposed in this document reducing the bandwidth available to
    RSVP-TE paths.  The former is possible whenever RSVP-TE and SR
    traffic share links, independently of whether this specification is
    in use; the latter is new behavior with this specifciation but is
    seen as preferrable to the alternative, since the impact to RSVP-TE
    traffic can be controlled and paths re-routed.  However, some latent
    risk of disruption remains because this specification is a reactive
    protcol, relying on taking measurements and only adopting to new
    traffic flows after the measurement period.  The finite duration of
    the measurement window leaves open a period of potential disruption
    before remediation can be applied.
 
[HS] Thanks for the suggestion. We can update the security section to the following:
[HS]
   This document describes solution options for the co-existence of
   RSVP-TE and SR LSPs in the same administrative domain.  The security
   considerations for SR are described in
   [I-D.ietf-spring-segment-routing].  The security considerations
   pertaining to RSVP-TE are described in [RFC5920].  The security
   considerations of each architecture are typically unaffected by the
   presence of the other.  However, when RSVP-TE and SR LSPs co-exist,
   it is possible for a hijacked SR traffic stream to maliciously
   consume sufficient bandwidth and cause disruption to RSVP-TE LSPs.
   With the solution option specified in Section 3.5, the impact to
   RSVP-TE traffic can be controlled and paths re-routed.  Some latent
   risk of disruption still remains because this solution option relies
   on taking statistics samples and adopting to new traffic flows only after
   the adjustment period.  The defensive mechanisms
   described in the base SR security framework should be employed to
   guard against situations that result in SR traffic hijacking or
   denial of service.    
[HS]
    
    This guidance seems like it could be (very) roughly characterized as
    "these are the ranges of values that are not insane to use".  Is it
    possible to give more precise/active guidance, such as (taking a
    wild guess) "Values between 0.9 and 1.1 allow for taking accunt of
    estimated future traffic growth during the current measurement
    period while reducing the risk of leaving large amounts of bandwidth
    underutilized.  The measurement period should be smaller than a
    minute in order for this tight of a growth window to make sense."

[HS] M is used to multiply SR traffic average at the adjustment period (N) and to update the maximum-reservable-bandwidth to over-state/under-state the actual availability. I'm not sure we can offer better guidance than to explain the effects of M < 1 and M > 1 and that choice is up to the operator, where the default of 1 is to not under/over-state.

--
Harish