Re: [Isis-wg] WG Last Call for draft-ietf-isis-auto-conf-04

"Les Ginsberg (ginsberg)" <ginsberg@cisco.com> Mon, 23 January 2017 00:36 UTC

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From: "Les Ginsberg (ginsberg)" <ginsberg@cisco.com>
To: "Acee Lindem (acee)" <acee@cisco.com>, Christian Hopps <chopps@chopps.org>, "isis-wg@ietf.org" <isis-wg@ietf.org>
Thread-Topic: [Isis-wg] WG Last Call for draft-ietf-isis-auto-conf-04
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Date: Mon, 23 Jan 2017 00:36:04 +0000
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Subject: Re: [Isis-wg] WG Last Call for draft-ietf-isis-auto-conf-04
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Acee -

> -----Original Message-----
> From: Acee Lindem (acee)
> Sent: Sunday, January 22, 2017 3:56 PM
> To: Les Ginsberg (ginsberg); Christian Hopps; isis-wg@ietf.org
> Cc: draft-ietf-isis-auto-conf@ietf.org; isis-chairs@ietf.org; isis-ads@ietf.org
> Subject: Re: [Isis-wg] WG Last Call for draft-ietf-isis-auto-conf-04
> 
> Hi Les,
> 
> On 1/22/17, 12:57 PM, "Les Ginsberg (ginsberg)" <ginsberg@cisco.com>
> wrote:
> 
> >Acee -
> >
> >Thanx for reviewing the document.
> >Responses inline.
> >
> >> -----Original Message-----
> >> From: Isis-wg [mailto:isis-wg-bounces@ietf.org] On Behalf Of Acee
> >>Lindem
> >> (acee)
> >> Sent: Sunday, January 22, 2017 5:39 AM
> >> To: Christian Hopps; isis-wg@ietf.org
> >> Cc: draft-ietf-isis-auto-conf@ietf.org; isis-chairs@ietf.org;
> >>isis-ads@ietf.org
> >> Subject: Re: [Isis-wg] WG Last Call for draft-ietf-isis-auto-conf-04
> >>
> >> Hi IS-IS WG,
> >>
> >> I have reviewed the document and support publication. I have the
> >>following  minor comments:
> >>
> >>     1. It should be made clear that the A-Bit indicates that an IS-IS
> >>router  supports auto-configuration and, is not, necessarily
> >>auto-configured itself.
> >> After reading the whole draft, I know that this is the definition of
> >>the bit but  the initial text says the router is ³operating in
> >>auto-configuration mode.²
> >
> >[Les:] It is clearly stated that the A flag does indeed mean
> >
> >" the router is operating in auto-configuration mode."
> >
> >I do not see any text which suggests otherwise.
> 
> But there is no prior definition of "auto-configuration mode". I think most
> readers would believe that this indicates that only routers performing auto-
> configuration will form adjacencies. Yet the documents
> states:
> 
>    This document also defines mechanisms to prevent the unintentional
>    interoperation of auto-configured routers with non-autoconfigured
>    routers.  See Section 3.3.
> 
> 
> Where is the interoperation? This definitely needs to be clarified - I don't see
> how the authors can argue on this point!
[Les:] Section 3.4.2.  Adjacency Formation

 "  Routers operating in auto-configuration mode MUST NOT form
   adjacencies with routers which are NOT operating in auto-
   configuration mode.  The presence of the Router Fingerprint TLV with
   the A bit set indicates the router is operating in auto-configuration
   mode."

I do not see that anything further is needed.
??

> 
> >
> >???
> >
> >>     2. In the duplicate detection in section 3.4.3, could you note
> >>that an IS-IS  router should be able to detect discern the case where
> >>two interfaces on the  IS-IS router performing auto-configuration are
> >>connected to the same  network.
> >>
> >[Les:] Multiple connections of the same system to the same network can
> >occur in the absence of auto-configuration and detection of this case
> >is not altered by auto-configuration. This is detected by receiving a
> >hello with the same source MAC address as a local interface. There are
> >then the following cases:
> >
> >1)Two interfaces on the local router are connected to the same media.
> >This is further validated by having the same systemID. The means for
> >detecting this as well as resolving this are not altered by
> >auto-configuration.
> >
> >2)Two neighbors connected to the same network have the same source
> MAC
> >address. This is distinguished by having different system IDs in the
> >hellos. The means for detecting this as well as resolving this are not
> >altered by auto-configuration.
> >
> >3)Two neighbors connected to the same network have the same source
> MAC
> >address and the same systemID. This is distinguished by having
> >different router fingerprint TLVs in the hellos - something only an
> >auto-config router could do. But the additional detection capability
> >does not provide any additional means to correct this issue.
> >
> >The authors discussed this point during the writing of the draft and
> >decided specifically NOT to comment on this issue as it by nature is no
> >different than what can occur without auto-config and there is no good
> >way to automatically recover from this case i.e. clearly we cannot
> >alter the physical connections by programmatic means - nor do we
> >assume/require a programmatic capability of assigning MAC addresses.
> >
> >So, I am not sure what we could say other than to note that this can
> >occur - but non-auto-config implementations already have to detect this
> >- so does it make sense to comment on this in the auto-config draft?
> 
> Given that consequences of this mis-wiring are more severe when IS-IS auto-
> configuration is being used, I think this deserves at least the discussion above
> included in the draft.
> 
[Les:] I do not see that this issue is any more/less severe when operating in autoconfig mode.
Manual intervention is required to resolve the issue regardless of mode - the protocol cannot heal itself in this case. All we can do is send out a notification and be smart in the implementation so as to avoid constant adjacency churn. This behavior is required/recommended regardless of autoconfig mode. In fact, it could be argued the problem is more severe for larger networks as the side effects of churn associated with sub-optimal handling of this problem will be far worse in a large network.

Interestingly, I do not even see a notification defined for this condition in the MIB (RFC 4444) - perhaps we will do better when defining the YANG data model. :-)

This is perhaps a problem worth discussing - but I don't see that it is in any way unique to or related to autoconfig - so adding it to this specification doesn't seem appropriate.

   Les


> Thanks,
> Acee
> 
> 
> 
> >
> >   Les
> >
> >
> >> Thanks,
> >> Acee
> >>
> >> On 1/17/17, 7:00 AM, "Isis-wg on behalf of Christian Hopps"
> >> <isis-wg-bounces@ietf.org on behalf of chopps@chopps.org> wrote:
> >>
> >> >
> >> >Hi Folks,
> >> >
> >> >We are starting a WG Last Call for
> >> >
> >> >  "ISIS Auto-Configuration"
> >> >  - https://datatracker.ietf.org/doc/draft-ietf-isis-auto-conf/
> >> >
> >> >The WGLC will expire in 2 weeks on Jan 31, 2017.
> >> >
> >> >Thanks,
> >> >Chris & Hannes.
> >>
> >> _______________________________________________
> >> Isis-wg mailing list
> >> Isis-wg@ietf.org
> >> https://www.ietf.org/mailman/listinfo/isis-wg