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

[Robert Raszuk <[e-mail]>]

​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.

Thx,
R.