Juliusz,

you could also inject the route with a 3rd party next-hop pointing to L.

cheers,
Ole


> On 16 Nov 2014, at 10:54 , Juliusz Chroboczek 
> <[email protected]> wrote:
> 
>>> If the latter, I can see some opportunities for transient routing loops
>>> if not done carefully.  (And you certainly don't want a routing loop on
>>> a link with low-power nodes.)
> 
>> That’s interesting. Could you try explaining what could happen ?
> 
> I hope I'm just being paranoid, since I rather like the idea of
> redistribution through HNCP.
> 
> A and B are homenet nodes.  L is a low power node.
> 
>   A-----B
>    \   /
>     \ /
>      L
>      |
>      |
>     LLN
> 
> A and B are both announcing the LLN route.  L crashes.  A and B both
> notice that L is no longer reachable, so each of them attempts to route
> through the other one.  You have a transient routing loop that lasts until
> A and B agree on the fact that L is unreachable.
> 
> On a wired network, the routing loop will be extremely short-lived (one
> successful packet exchange for both Babel and OSPF, not sure about IS-IS).
> I'm not sure what will happen on a wireless network, but I've learnt to be
> pessimistic about the behaviour of 802.11.  I could imagine cases where
> the looping data traffic prevents A and B from communicating successfully,
> especially if L had more than just two Homenet neighbours.
> 
> In the case of Babel (or EIGRP, for that matter), running a stub
> implementation on L solves the problem quite nicely, by allowing the
> loop-avoidance algorithm to kick in before the loop is established.  With
> link state, you still get a transient loop, but you're relying on the
> carefully designed flooding algorithm of a mature routing protocol to
> clear it, rather than counting on the poorly understood interactions
> between the routing protocol and HNCP happening in the right order.
> 
> -- Juliusz
> 
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