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

[Tony Li <[e-mail]>]

Hi Les,

> 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)


In fact, without the reverse metric TLV, you cannot do this at all.  Without extending the protocol is _some_ way, you are not allowed to have a non-zero metric in the pseudonode.  Further, Shane's survey suggests that there is sufficient variation in implementations that it is unsafe to advertise a non-zero pseudonode metric without some flag day for the domain anyway.


> Frankly, I am not seeing this benefit as very compelling. The big win on
> the LAN is the introduction of the ability to use something other than 0
> in the pseudo-node LSPs - and that can be done (with the same amount of
> risk) without the Reverse Metric TLV by configuring it on the DIS.


The ability to make one link of an L2 switching domain into a link of last resort seems like it is compelling to me, and the ability to do so from the system itself seems like a significant simplification for operations.  One less thing to go wrong when the operator doesn't can't fumble finger the manually entered system ID.  Or applies the configuration to a system other than the DIS.

Tony