Re: [Isis-wg] draft-amante-isis-reverse-metric-01

[Shane Amante <[e-mail]>]

Les,

Thanks for your feedback.  I'm rewinding this thread a bit, because I disagree with your summary below.  

See below.

On Dec 5, 2010, at 23:30 MST, Les Ginsberg (ginsberg) wrote:
> Shane -
> 
> The revised draft is significantly clearer. Thanx.
> 
> I am still struggling with the justification for the Reverse Metric TLV.
> Let me try to summarize the differences between available solutions to
> the problem with/without the Reverse Metric TLV.
> 
> Point-Point Circuits
> ----------------------
> 
> Without Reverse Metric TLV: Must change metric configuration on both
> neighbors
> 
> With Reverse Metric TLV: On one neighbor change the local metric AND
> configure the reverse metric to be sent to the other neighbor
> 
> The difference is then one config change on two neighbors vs two config
> changes on one neighbor.
> 
> Multi-Access LANs
> -----------------
> 
> Without Reverse Metric TLV: On the DIS must configure max metric to be
> sent in p-node LSP on the DIS for the neighbor(s) of interest (or ALL
> neighbors)
> 
> With Reverse Metric: Must configure the reverse metric to be sent to the
> DIS on each neighbor of interest - or in the case of impacting ALL
> neighbors the reverse metric config an be done on any neighbor (DIS or
> non-DIS)
> 
> The difference is then whether the config change MUST be done on the DIS
> or may be done on any neighbor on the LAN.
> 
> Would you agree with this summary?

In summary, no.  :-)  The goal of this draft is that there is a _single_ configuration change required, on just one router, which would simultaneously add/increase the metric to both:
a)  the local router's interface; and,
b)  the remote router's interface facing the local router.

This is discussed, (but perhaps not clearly enough), in:
1)  Section 3.5, Operational Guidelines, where we state that IS-IS routers MUST NOT modify their existing IS-IS metric, (thus the configuration of Reverse Metric is _adding_ to what's already there):
---snip---
   During the period when a Reverse Metric TLV is used, IS-IS routers
   that are generating and receiving a Reverse Metric TLV MUST NOT
   change their existing IS-IS metric or Traffic Engineering parameters
   in their stored (e.g.: hard disk, etc.) configurations, since those
   parameters are carefully derived from off-line capacity planning
   tools and are difficult to restore to their original values.
---snip---
2)  Section 4, "Reverse Metric TLV Use Case".  Although this is a non-normative section, it hopefully expresses what is expected when the Reverse Metric is used in a network and seems fairly clear that only a single configuration change (to add the reverse-metric cfg) is occurring.

Does that satisfy your concerns?  If not, can you suggest text that would make this more clear?

Thanks,

-shane



>   Les
> 
> 
>> -----Original Message-----
>> From: [e-mail] [mailto:[e-mail]] On
>> Behalf Of Shane Amante
>> Sent: Monday, November 29, 2010 10:26 PM
>> To: isis mailing list
>> Subject: [Isis-wg] draft-amante-isis-reverse-metric-01
>> 
>> Hi Everyone,
>> 
>> The authors wish to announce a new version of this draft has been
>> published.  It is a substantial revision from the -00 version, based
> on
>> comments received on the list.  Some of the notable, high-level
> changes
>> are as follows:
>> - changed the procedure so that a receiver of a Reverse Metric TLV
>> treats the recv'd Metric value as 'additive' to its existing,
>> configured default-metric (instead of 'overwriting' its existing,
>> configured default-metric);
>> - narrowed the scope of the draft to discuss only making changes to a
>> neighbor's default-metric;
>> - added support for MT-ISIS;
>> - added Security Considerations section;
>> ... as well as a substantial overall reorganization to hopefully make
>> the draft easier to read and follow.
>> 
>> We welcome your comments and questions.
>> 
>> Thanks!
>> 
>> -shane
>> 
>> ---snip---
>> A New Internet-Draft is available from the on-line Internet-Drafts
>> directories.
>> 
>> 	Title           : IS-IS Reverse Metric TLV for Network
>> Maintenance Events
>> 	Author(s)       : N. Shen, et al.
>> 	Filename        : draft-amante-isis-reverse-metric-01.txt
>> 	Pages           : 13
>> 	Date            : 2010-11-29
>> 
>> This document describes an improved IS-IS neighbor management scheme
>> which can be used to enhance network performance by allowing
>> operators to quickly and accurately shift traffic away from a point-
>> to-point or multi-access LAN interface by allowing one IS-IS router
>> to signal to a second, adjacent IS-IS neighbor to adjust its IS-IS
>> metric that should be used to temporarily reach the first IS-IS
>> router during network maintenance events.
>> 
>> A URL for this Internet-Draft is:
>> http://www.ietf.org/internet-drafts/draft-amante-isis-reverse-metric-
>> 01.txt
>> ---snip---
>> 
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