Re: [Teas] Benjamin Kaduk's No Objection on draft-ietf-teas-assoc-corouted-bidir-frr-06: (with COMMENT)

["Rakesh Gandhi (rgandhi)" <[e-mail]>]

Hi Benjamin,

Thank you for the detailed review. Please see inline replies with <RG>…

On 2018-10-24, 11:12 PM, "Benjamin Kaduk" <[e-mail]> wrote:

    Benjamin Kaduk has entered the following ballot position for
    draft-ietf-teas-assoc-corouted-bidir-frr-06: No Objection
    
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    ----------------------------------------------------------------------
    COMMENT:
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    How does the unidirectional link failure logic and the revertive logic
    interact?  That is, in the unidirectional failure case a node should be
    detecting that there is a failure case and rerouting reverse traffic onto
    the protection path to match the forward path.  But a node in the process
    of reverting back on to the primary path (before its counterpart in the
    other direction) would seem to observe the same packet/path behavior as in
    the case of a unidirectional link failure.  Do we need to rely on the
    flooding of link status information to differentiate between these cases?

<RG> The basic idea is as following: After FRR, RSVP messages are sent with modified “IPV4 tunnel sender address" in the SENDER_TEMPLATE Object of the protected LSP, this is how the receiving node knows if FRR has been triggered and it can use it to trigger co-route. After revertive back when the failure is repaired, the RSVP Path message SENDER_TEMPLATE is restored as before [RFC4090, Section 6.5.2], which can be then used by the receiving node to trigger revertive behavior.

<RG> Yes, flooding link status / topology database can be used for Global revertive behavior.


    Are the state-keeping and resource consumption burdens large for the
    midpoint nodes that now must correlate whether they see traffic on
    original/protection paths for associated flows?  (E.g., Section 4.1.3's
    "when it receives the un-modified RSVP path messages and traffic".)
    It seems like it should just be a linear scaling factor at worst, with no
    real path to an attack, but perhaps there are security considerations
    relating to router capacity.
   

    Section 2
    
       In packet transport networks, there are requirements where the
       reverse LSP of a bidirectional LSP needs to follow the same path as
       its forward LSP [RFC6373].  [...]
    
    Does this need a qualifier (e.g., "some packet transport networks" or
    "there are sometimes requirements")?

<RG> Updated to “some packet transport networks”.
    
    
    Section 3.2
    
       tunnel S (on path B-F-G-D) to reach downstream MP node D whereas the
       upstream PLR node C reroute the protected reverse LSP2 traffic over
       the bypass tunnel N (on path C-I-H-A) to reach the upstream MP node
       A.  [...]
    
    nit: "reroutes"

<RG> Fixed.
    
    Section 4.1.1
    
       As shown in Figure 2, when using a node protection bypass tunnel with
       protected co-routed LSPs, asymmetry of paths can occur in the forward
       and reverse directions after a link failure [RFC8271].  In order to
       restore co-routing, the downstream MP node D (acting as an upstream
       PLR) SHOULD trigger the procedure to restore co-routing and reroute
       the protected reverse LSP2 RSVP Path messages and traffic over the
       bypass tunnel S (on path D-G-F-B) to the upstream MP node B upon
    
    Why is this only a SHOULD?

<RG> It is MUST to restore co-route. Updated.

    
    Section 4.2
    
                                                            An endpoint node
       MAY set the Extended Association ID to the value shown in Appendix A.
    
    The contents of Appendix A do not include a distinguished single value, but
    rather a data structure, so I think that a phrase other than "to the
    value" should be used.

<RG> Updated using suggestion from Adam Roach as: "... set the Extended Association ID to a value formatted according to the
structure shown in Appendix A."
    
       o  For double-sided provisioned bidirectional LSPs [RFC7551], both
          endpoints need to ensure that the bidirectional LSP has a unique
          Extended ASSOCIATION Object for each forward and reverse LSP pair
          by selecting appropriate unique Extended Association IDs signaled
          by them.
    
    How does this signalling/selection process get the two endpoints to agree
    on the same value?

<RG> Added text: A controller can be used to provision unique Extended Association ID on both endpoints.  The procedure for selecting unique Extended Association ID is outside the scope of this document.  
    
    Appendix A
    
    (Again, "to the value" is not appropriate to describe the general format.
    Perhaps, "to a value using the format".)
    
<RG> Updated as above.

    Please also explicitly describe the semantics of the "Reserved" field(s)
    (i.e., set to zero on transmission and ignored on receipt).
    
<RG> Added.

Thanks,
Rakesh