On Aug 6, 2009, at 5:06 PM, Joakim Tjernlund wrote:
Consider this example:
R1 R2 R3
| | |
------- N1
Destination is R3 and R2 is the calculation router. R2 cannot find a
backlink
so it falls back to the intervening router case and uses the
nexthops
from the "parent", hoping that one of them will redirect IP frames
to
R3.
This is an uninteresting case, as there are no alternative paths.
Yes, it is very simple to make it clear what I am after.
Further, there will be no "intervening router" in this case, since
each of R1, 2, and 3 will be adjacent to only N1.
Yes, I am just saying that in this particular case I want apply the
same SPF rules as the intervening router uses.
But there is no intervening router to inherit the next hops from, so
the particular point is moot. But in the broader context, yes, it
would be possible to simply declare R3 to be the next hop, assuming
that R2 has heard Hello packets from it on the wire, but as you gather
this isn't such a good idea.
Where it can get much uglier is if there is a back path between R2
and
R3; other routers playing properly will try to send the traffic
through R3, but R3 will try to forward it locally.
hmm, don't you mean "through R2, but R2" ?
Yes, my mistake.
In this case it
will probably result in the traffic just disappearing down a hole
instead of being properly delivered on the alternative path. But if
you start playing these games more generally, you can end up with
traffic flying in circles.
I am starting to think that my idea was a bad idea now :)
Stick with that thought. ;-)
--Dave
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