[OSPF] Re: Comments on draft-berger-ospf-rfc2370bis-00.txt

Acee Lindem <acee@cisco.com> Mon, 20 November 2006 23:37 UTC

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Date: Mon, 20 Nov 2006 18:37:45 -0500
From: Acee Lindem <acee@cisco.com>
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To: Lou Berger <lberger@labn.net>
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Subject: [OSPF] Re: Comments on draft-berger-ospf-rfc2370bis-00.txt
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Hi Lou,
See inline.

Lou Berger wrote:
> Acee,
>         See responses in-line below.
> Should the corrected version go in as draft-berger or draft-ietf?
> Lou
> At 07:03 PM 11/13/2006, Acee Lindem wrote:
>> Hi Lou,
>> My main comment is on section 5 (6 is your draft). The draft adds
>> mandatory reachability checking for AS scoped opaque LSAs.
>> If we add mandatory reachability checking, it should be for all
>> opaque types rather reading like the constraint is unique to AS scoped
>> opaque LSAs (type 11s).
> valid point.
>> I also think we should put the question as to whether the checking
>> should be madatory or relaxed a bit to allow an application to check
>> less frequently if the opaque data is stale.
> What benefit would this have?
This would allow applications that don't require the opaque data to
strictly track the SPF to discontinue using the information less frequently
than the SPF. This would be useful if OSPF and the application using the
opaque data were not tightly coupled. Here is what I put in the OSPFv3
update draft:

3.4.4.  Future LSA Validation

   It is expected that new LSAs will be defined that will not be
   processed during the Shortest Path First (SPF) calculation as
   described in Section 3.8.  For example, OSPFv3 LSAs corresponding to
   information advertised in OSPFv2 using opaque LSAs [OPAQUE].  In
   general, the new information advertised in future LSAs should not be
   used unless the OSPFv3 router originating the LSA is reachable.
   However, depending on the application and the data advertised, this
   reachability validation MAY be done less frequently than every SPF

   To facilitate inter-area reachability validation, any OSPFv3 router
   orginating AS scoped LSAs is considered an AS Boundary Router (ASBR).

On the other hand, there is a school of thought that would consider this an
implementation detail. I, however, think it is better if it is 
explicitly stated.
If, for no other reason, to provide guidance to the people testing the 
>> Detailed comments:
>> Section 2, third paragraph - "aligned" rather than "qaligned".
> yes.
>> Section 3, "Section 7" rather than "Section 7."
> okay.
>> Section 3.1 - Type 9  LSA - "keep" rather than "keepk".
> yes.  Also I added the following to the beginning of the section:
>  Section 13 of [OSPF] describes the OSPF flooding procedure.
>  Those procedures MUST be followed as defined except where
>  modified in this section.
>> I believe we
>>                    should discard a link-local LSA received from a 
>> neighbor not
>>                    on the interface (text similiar to type 11).
> okay, updated as follows:
>   o If the Opaque LSA is type 9 (the flooding scope is link-local)
>     and the interface that the LSA was received on is not the same
>     as the target interface (e.g., the interface associated with a
>     particular target neighbor), the Opaque LSA SHOULD be discarded
>     and not acknowledged, and MUST NOT be flooded out that interface
>     (or to that neighbor).  An implementation SHOULD keep track of
>     the IP interface associated with each Opaque LSA having a
>     link-local flooding scope.
I guess I think that if you discard an LSA, it is implied that you won't
reflood it.

>> Section 3.1, Since the area ID is not in the LSA header, the bullet on
>>                   area flooding is confusing. It should say something 
>> to the
>>                   effect of only flooding type 10 LSAs out interfaces 
>> in the
>>                   LSA's associated area.
> okay, updated as follows:
>   o If the Opaque LSA is type 10 (the flooding scope is area-local)
>     and the area associated with Opaque LSA (as identified during
>     origination or from a received LSA's associated OSPF packet
>     header) is not the same as the area associated with the target
>     interface, the Opaque LSA MUST NOT be flooded out the interface.
>     An implementation SHOULD keep track of the OSPF area associated
>     with each Opaque LSA having an area-local flooding scope.
I think the action should be same as above. In any case, this can never
happen as the entire Link State Update packet would be discarded.

>> I don't care if it said this in RFC 2370
>>                   and everyone knew what it implied.
> I don't know how to interpret the text otherwise...
RFC 2328 specifically state that packets whose Area ID cannot
be matched to the receiving interfaces are discarded. See section 8.2.

>> Section 3.1, 2nd to last paragraph: "An opaque" rather than "a opaque".
> okay.
>> Swap sections 5 and 6 since "inter-area" is more the "meat" of the 
>> draft.
> done.
>> In fact, if the opaque MIB objects are all covered in the new MIB, we 
>> can
>> probably remove the "management section".
> done, section will read:
>   The updated OSPF MIB provides explicit support for opaque LSAs and
>   SHOULD be used to support implementations of this document.  See
>   Section 12.3 of [MIB-UPDATE] for details.  In addition to this section,
>   implementation supporting [MIB-UPDATE] will include opaque LSAs in
>   all appropriate generic LSA objects, e.g., ospfOriginateNewLsas,
>   ospfOriginateNewLsas and ospfLsdbTable.
> BTW just sent WG mail on one inconsistency between 2370 and the 
> updated MIB.
>> Section 6 (will be 5)
>> 5. Opaque LSA Validation
>> Opaque LSAs are not processed during the SPF calculation as described in
>> section 16 of [OSPF]. However, they are subject to the same reachability
>> constraints as the base LSA types. This implies that originating router
>> MUST be reachable for the advertised application specific data to be
>> considered valid.
>> 5.1 Inter-Area Considerations
>> ......
>> Section 5.1
>>   Type-9 opaque LSAs and type-10 opaque LSAs do not have this problem
>>   as a receiving router can detect an a loss of reachability through 
>> the intra-area
>>   SPF calculation.
>> Section 5.1
>>   To enable OSPF routers in remote areas to check availability of the
>>   originator of link-state type 11 opaque LSAs, the orignators of
>>    type-11 opaque LSAs are considered Autonomous System Border
>>    Routers (ASBRs) and will advertise themselves as such.
>> Section 5.1 - Remove "It is important to note that this solution MUST 
>> NOT ..."
>> This is redundant.
> which part is redundant, just the sentence you are asking to be 
> removed?  I agree that it is redundant with 2328, but I thin 
> mentioning it is still useful.  Will rephrase to remove directive.
This part of the specification doesn't modify stub area behavior.
Here, we are talking about validating AS scoped opaque LSA.
I guess you could say, "Note that AS scoped opaque LSA
validation is not applicable to stub and NSSA areas since LSAs
with AS scope are not flooded into these areas types." However,
I don't see it as necessary.

>> Remove numbered items (1) and (2), these actions ARE NOT new to
>> opaque LSAs. Make (3) a separate paragraph rather than numbered
>> item.
> But inclusion of type-11 originate routers as ASBR is new.  Will 
> rephrase to make clear that existing ospf requirements apply.
> How about:
> The procedures related to inter-area opaque LSAs are as follows:
> (1) An OSPF router that is configured to originate AS-scope opaque
>     LSAs advertise themselves as ASBRs and MUST follow the related
>     requirements related to setting of the  Options field E-bit in
>     OSPF Hello packets and LSA headers as specified in [OSPF].
> (2) When ....
I don't think these points need to be restated even if they reference
RFC 2328. Opaque LSAs don't modify these conditions. Hence,
I don't see them to be required any more than stating the version field
the OSPF packet header should be set to 2.
>> Section 10.1 - Correct NSSA reference to RFC 3101.
> thanks.
>> Section 12.1 - Add D and MT bits with informative references to [RFC 
>> 4576]
>> and the [OSPF-MT] drafts. "All eight bit ..." rather than "Six bits..".
> done.
>> General - Replace "stub area" with "stub or NSSA areas".
> sure.
>> Thanks,
>> Acee
> Great comments.

> Much thanks.
> Lou

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