IP and Optical domains?

Mon Jun 20 10:14:27 UTC 2016

On 20/Jun/16 11:59, Masataka Ohta wrote:

>
> The problem is not optical at all but caused by poor L3 routing
> protocols and operational attempts to compensate them at L2.

Ummh, how so.

Layer 2 transport is required in any scenario. Dark fibre, for example,
would not have any optical kit on it, and can be fired through
router-to-router optics. How is this any different from a routing
perspective?

>
> That is, with a L3 routing protocol having 1ms of HELO
> intervals, all the thing to be done at L2 is to watch BER/FER
> above some threshold.

Ummh, BFD works, and this can be used even in grey-light situations
where the router has no DWDM visibility into the link state.

>
> To act against failures.

Or to support growth.

>
> But, if everything is visible at L3, over-provisioned bandwidth
> can be used even if there is no failure.

We primarily over-provision to support growth. Resiliency comes as
secondary benefit.

If you are deploying additional bandwidth just for protection, I hope
you're my competitor.

>
> Visible at L3 means that parallel point to point links
> between a pair of routers have distinct pairs of IP addresses
> and BGP routes should flip only upon failure of all the
> (or almost all the) links.

iBGP uptime is par for the course.

The main advantage of having parallel links across the same path is to
increase bandwidth (through load balancing). This is an IGP operation.

>
> A remaining, but minor, inefficiency could be mismatch of metric
> at L1 and L3, that is, ASPATHLEN increases for transit
> services are not roughly proportional to geographic distances
> of the transit services.

If the circuits are on-net, BGP takes the IGP metric into account when
trying to get to a target NEXT_HOP.

AS_PATH length is an inter-domain concept. One has to manage their eBGP
routing using those protocol specific methods to manage latency. This is
where a successful operator out-maneuvers their competition, so I don't
see it as a protocol or transport limitation, per se.

Mark.