Re: I-D Action: draft-voyer-6man-extension-header-insertion-02.txt

[Tom Herbert <[e-mail]>]

On Sat, Dec 2, 2017 at 11:01 AM, Robert Raszuk <[e-mail]> wrote:
> Tom,
>
>>
>> However, in that case why not do the
>> segment routing at the ingress node of the domain in conjuction with
>> the encapsulation and avoid the complexities needed to make EH
>> insertion work correctly?
>
>
> Because in this particular case what is being done is a *local repair*.
> Local means that packets are redirected at the node which first notices the
> failure (usually adjacent to the link or node failure) which is maximum
> order of 10s of ms. Yes FIBs/data plane of those nodes are programmed ahead
> of failures with backup rewrites too.
>
> There is no time to propagate such information in the control plane to
> ingress such that new/adjusted SRH is imposed to achieve comparable repair
> results. That is happening in parallel to packets already being under local
> protection, but takes 100s of ms or even seconds for all control plane to
> converge.
>
> That is what we call fast connectivity restoration vs protocol convergence.
> Completely different things.
>
> So yes there are networks which only use control plane convergence OSPF/ISIS
> or even BGP and do nothing to protect packets locally when failure occurs
> but those are very bad examples of network design or choice of vendors which
> can not perform local repairs.
>
Thanks for the detail Robert. Has there been any thought into using
the flow label to switch the packet over alternate paths? That might
be a zero overhead solution :-)

Tom