Re: [Lsr] Benjamin Kaduk's Discuss on draft-ietf-isis-mpls-elc-12: (with DISCUSS and COMMENT)

["Acee Lindem (acee)" <[e-mail]>]

Hi Peter, 

On 5/26/20, 8:22 AM, "Peter Psenak" <[e-mail]> wrote:

    Hi Acee,

    have you looked at the texts that I suggested in my response to Alvaro 
    earlier today?

I found it - let me reply to that Email.

Thanks,
Acee


    Please see inline:

    On 26/05/2020 13:49, Acee Lindem (acee) wrote:
    > Hi Alvaro,
    > 
    > See inline.
    > 
    > On 5/22/20, 10:59 AM, "Alvaro Retana" <[e-mail]> wrote:
    > 
    >      On May 21, 2020 at 3:39:03 PM, Benjamin Kaduk wrote:
    > 
    > 
    >      Peter:
    > 
    >      Hi!
    > 
    > 
    >      > With respect to Alvaro's clarification, your answer for (1) makes sense;
    >      > thanks! I think Alvaro has offered to help work out what (if any)
    >      > additional text we might want to be sure that the answer to (2) is clear in
    >      > the document.
    > 
    >      I think that #1 is where some clarification could be useful. :-)
    > 
    > 
    >      I'm including both ISIS and OSPF suggestions below to consolidate the
    >      discussion.
    > 
    > 
    >      ...
    >      > > My interpretation of Ben's question is two-fold:
    >      > >
    >      > > (1) Would ISIS routers normally propagate the information to a
    >      > > different level? The ELC is a new prefix attribute flag -- are prefix
    >      > > attributes always propagated (unchanged) to other levels? If so, then
    >      > > the requirement (MUST) is not needed. My reading of rfc7794 is that
    >      > > the propagation is optional...
    >      >
    >      > depends on the attribute or a bit. Some are propagated some are not.
    >      > That's why we are saying this one MUST be preserved.
    > 
    >      Right.
    > 
    >      For ISIS I think the current text is in line with the specification of
    >      the other bits in rfc7794.  No changes are needed.
    > 
    >      If anything, you may want to change the order of this sentence to
    >      address Ben's comment:
    > 
    >      OLD>
    >         When a router propagates a prefix between ISIS levels ([RFC5302], it
    >         MUST preserve the ELC signaling for this prefix.
    > 
    >      NEW>
    >         The ELC signaling MUST be preserved when a router propagates a prefix
    >         between ISIS levels ([RFC5302]).
    > 
    >      [Similar for OSPF.]
    > 
    > 
    > 
    >      I think that for OSPF it is not that simple...
    > 
    >      For OSPFv2: rfc7684 says that the "scope of the OSPFv2 Extended Prefix
    >      Opaque LSA depends on the scope of the advertised prefixes", which I
    >      assume means that for intra-area prefixes the scope will be
    >      area-local...so the ABR wouldn't simply propagate it; it would have to
    >      originate a new LSA.
    > 
    > I agree with the changes but have suggested alternate text.
    > 
    >      Suggestion (Add to 3.1)>
    >         When an OSPFv2 Area Border Router (ABR) distributes information between
    >         connected areas it SHOULD originate an OSPFv2 Extended Prefix Opaque LSA
    >         [RFC7684] including the received ELC setting.  If the received information
    >         is included in an LSA with an AS-wide scope, then the new LSA is not needed.

    when would ABR do inter area propagation of what is advertised in AS 
    scope LSA? I can not think of such a case.

    thanks,
    Peter


    > 
    > I'd suggest:
    > 
    >        When an OSPFv2 Area Border Router (ABR) advertises prefix information between
    >        areas and ELC information is was advertised for the prefix in the source area, the
    >        ABR SHOULD originate an OSPFv2 Extended Prefix Opaque LSA [RFC7684] propagating
    >        the prefix's source area setting. If the ELC setting, is also advertised in an OSPFv2
    >        Extended Prefix Opaque LSA with AS-wide scope, the additional LSA origination
    >        Is not needed.
    > 
    > 
    >      For OSPFv3: The PrefixOptions are *in* the LSA, but I couldn't find
    >      anything in rfc5340 saying that the received values should be copied
    >      into the Inter-Area-Prefix-LSA (nor that they should not).
    > 
    >      Suggestion (Add to 3.2)>
    >         When an OSPFv3 Area Border Router (ABR) distributes information between
    >         connected areas, the setting of the ELC Flag in the Inter-Area-Prefix-LSA
    >         MUST be the same as the received value.
    > 
    > I'd suggest:
    >        
    >        When an OSPFv3 Area Border Router (ABR) advertises information between
    >        areas, the setting of the ELC flag in the Inter-area-prefix-LSA MUST be the
    >        propagated unchanged.
    > 
    > Thanks,
    > Acee
    > 
    > 
    > 
    > 
    >      > > (2) If the propagation is not automatic, and the L1L2 router doesn't
    >      > > support this specification, then what are the drawbacks/failure
    >      > > scenarios? IOW, for multi-level operation is it a requirement that
    >      > > the L1L2 support this specification?
    >      >
    >      > drawback are identical to what is mentioned in the Security
    >      > Considerations section.
    > 
    >      I think that text is ok.
    > 
    > 
    >      Thanks!
    > 
    >      Alvaro.
    > 
    > 
    >