I support the progression of this document, but would like to see the
comments Stewart and I made earlier on the algorithm addressed and also
the few points below.
In addition, I wonder whether there should be something up front which
makes clear that this may only provide a partial solution (depending on
the topology). I know this is implicit in the body of the text, but I
think it would be useful to avoid any misunderstandings if the abstract
were a little more explicit on this point.
How about adding after "...The goal of this technology is to reduce the
micro-looping and packet loss that happens while routers converge
after a topology change due to a failure. ..."
"The extent to which this goal can be met by this specification is
dependant on the topology of the network."
1.1. Failure Scenarios
The alternate next-hop can protect against a single link failure, a
single node failure, one or more shared risk link group failures, or
a combination of these.
It might be better to say "failure of one or more links within a shared
risk link group".
Figure 5: Example where Continued Use of Alternate is Desirable
This is an example of a case where the new primary is not a loop-free
alternate before the failure and therefore may have been forwarding
traffic through S. This will occur when the path via a previously
upstream node is shorter than the the path via a loop-free alternate
neighbor. In these cases, it is useful to give sufficient time to
ensure that the new primary neighbor and other nodes on the new
primary path have switched to the new route.
I wonder if it should be pointed out that while this is a good strategy
to minimize the occurrence of microloops, it does nothing to prevent any
microloops which may occur more than one hop away.
based on the new network topology. The use of the alternate next-
hops for packet forwarding SHOULD terminate:
a. if the new primary next-hop was loop-free prior to the topology
b. if a configured hold-down, which represents a worst-case bound on
the length of the network convergence transition, has expired, or
c. if notification of an unrelated topological change in the network
We should probably add that if the primary link comes back before any of
this has happened then you can just go back to using the primary link as
if nothing had happened. That of course pre-supposes that the failure
hadn't yet been advertised. If it HAS been advertised, then it requires
another advertisement to put it back how it was, but in any case (I
think) the old next hop can safely be used.
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