Re: [OSPF] OSPF WG Minutes from IETF 95

"Acee Lindem (acee)" <acee@cisco.com> Thu, 14 April 2016 13:40 UTC

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From: "Acee Lindem (acee)" <acee@cisco.com>
To: "Alvaro Retana (aretana)" <aretana@cisco.com>, Paul Jakma <paul@jakma.org>
Thread-Topic: [OSPF] OSPF WG Minutes from IETF 95
Thread-Index: AQHRk+ug+9xkeFSUNUaQhV0sMu+UBZ+E5gwAgANQ+gD//9JIAIAAlAqA///jKQCAAT2+gP//wDYA
Date: Thu, 14 Apr 2016 13:40:07 +0000
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References: <D330445B.58C7B%acee@cisco.com> <04479c8fba16697eb3a51ea89d0cd708@zeta2.ch> <D3313626.58E6F%acee@cisco.com> <alpine.LFD.2.20.1604131455120.18471@stoner.jakma.org> <D333DB19.59F07%acee@cisco.com> <alpine.LFD.2.20.1604132106430.13056@stoner.jakma.org> <D3343D78.5A358%acee@cisco.com> <D3350F54.11EDC1%aretana@cisco.com>
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Cc: OSPF WG List <ospf@ietf.org>
Subject: Re: [OSPF] OSPF WG Minutes from IETF 95
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<hat>Author of compliment implementation</hat>

Hi Alvaro, 

I don’t necessarily agree that the only case where the links with
MaxLinkMetric will be used is when there is no other path. One could have
a situation where an alternate path existed but the aggregate cost was
greater than 64K. I agree this is highly unlikely in real deployments but
very likely in test topologies. Hence, I’d leave the section 4 text as is
and modify the section 3 text.


   MaxLinkMetric
      The metric value indicating that a router-LSA link (see Section 2)
      should strongly discourage the usage for transit traffic.  It is
      defined to be the 16-bit binary value of all ones: 0xffff.


Thanks,
Acee 


On 4/14/16, 9:28 AM, "Alvaro Retana (aretana)" <aretana@cisco.com> wrote:

>On 4/13/16, 6:31 PM, "OSPF on behalf of Acee Lindem (acee)"
><ospf-bounces@ietf.org on behalf of acee@cisco.com> wrote:
>
><hat>author<hat>
>
>Acee:
>
>Hi!
>
>>>Sure, 4 reads the other way but "deployment considerations" . I'm not
>>>saying how it must be read, just saying it is possible to read the
>>>stronger language of 3 another way.
>>>
>>>I'm not trying to argue, I'm trying to explain why we are here.
>>
>>One of the authors or myself will write an errata to clarify this
>>definition.
>
>What do you have in mind?
>
>I may be too close to the text myself to tell where we should change
>something.  Even if we interpret the "should not" in Section 3 as if it
>was "SHOULD NOT", it is still not a "MUST"...and the obvious reason the
>link would be used is if there isn't another path.
>
>There is one part which I think can be clarified (only including the
>change):
>
>NEW>
>4.  Deployment Considerations
>...
>   on using them rather than the path through the stub router.  If the
>   path through the stub router is the only one, the routers of the
>   first type will not use the stub router for transit, while the routers
>   of the second type will still use this path, which may result in a
>routing 
>   loop.
>...
>
>
>
>I'm open to other suggestions.
>
>Thanks!
>
>Alvaro.
>
>
>
>CURRENT TEXT>
>3.  Maximum Link Metric
>
>   Section 2 refers to the cost of all non-stub links as MaxLinkMetric,
>   which is a new fixed architectural value introduced in this document.
>
>   MaxLinkMetric
>      The metric value indicating that a router-LSA link (see Section 2)
>      should not be used for transit traffic.  It is defined to be the
>      16-bit binary value of all ones: 0xffff.
>
>4.  Deployment Considerations
>
>   When using MaxLinkMetric, some inconsistency may be seen if the
>   network is constructed of routers that perform an intra-area Dijkstra
>   calculation as specified in [RFC1247] (discarding link records in
>   router-LSAs that have a MaxLinkMetric cost value) and routers that
>   perform it as specified in [RFC1583] and higher (do not treat links
>   with MaxLinkMetric cost as unreachable).  Note that this
>   inconsistency will not lead to routing loops, because if there are
>   some alternate paths in the network, both types of routers will agree
>   on using them rather than the path through the stub router.  If the
>   path through the stub router is the only one, the routers of the
>   first type will not use the stub router for transit (which is the
>   desired behavior), while the routers of the second type will still
>   use this path.
>
>   On the other hand, clearing the R-bit will consistently result in the
>   router not being used for transit.
>
>   The use of MaxLinkMetric or the R-bit in a network depends on the
>   objectives of the operator.  One of the possible considerations for
>   selecting one or the other is in the desired behavior if the path
>   through the stub router is the only one available.  Using
>   MaxLinkMetric allows for that path to be used while the R-bit
>   doesn't.
>
>