Subject: Re: [Isis-wg] operational problem might be solved by somehowextending current IS-IS

From: [email-masked]
Date: Thu, 16 Sep 2010 20:17:38 +0200

"applying max-metric to every adjacency of the pseudo-node will not alter
relative cost between various routers on the segment, so would need to
specify that only metric from the pseudo-node to specific router should
be changed (ok, this are just details). Login to DIS method might seem
attractive, but what happens when DIS function moves to another router -
new DIS won't have slightest idea that it needs to apply non-zero metric
to some pseudo-node adjacency. Therefore the only solution is for the
router, that wants its interface used only as last resort, to signal
others that reverse metric should be changed."

Hi iLya,

You mean to signal DIS for increase reverse metric in above case?

Guan

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From: Ilya Varlashkin <[email-masked]>
Date: Thu, 16 Sep 2010 20:53:23 +0200

> You mean to signal DIS for increase reverse metric in above case?

As one option - yes. Second option would be that this reverse increase done not by DIS itself, but by the node performing calculation. To demonstrate it on example: consider R1 wants to increase reverse cost of its interface, it adds (new, lets call it 'reverse cost') TLV to its LSP which can be either true/false (=='set reverse metric to be equal to IS-Reach metric') or literally value of desired reverse cost. When DIS receives this TLV it does NOT take it into account when generating pseudonode LSP, however every router performing SPF calculation ignores zero cost from pseudo-node to R1 and instead applies cost dictated by 'reverse cost' TLV. The rest of the protocol remains unchanged. I have not yet considered pro's and con's of either approaches.

/iLya