[Olsr-users] Route convergence time: a function of scale?

[Henning Rogge]

Am Monday 08 December 2008 14:32:00 schrieb Breno Jacinto:
> Hello,
>
>      This is my first post, nice to be here sharing knowledge with you
> guys. I have a question that has been in my head for a while.
>
>      Consider that there's an OLSR network, and some nodes (20, for
> exemple) are part of it. Now, given that OLSR is a pro-active
> protocol, it's assumed that, for those 20 nodes, each has a route for
> each other, whether single-hop(they are neighbors) or multi-hop (some
> nodes make a node see another, more distant node).
>
>      OK, now, consider that I wish to test if a given node address,
> 192.168.10.15, is on the network. So:
>
> # ping 192.168.10.15
>
>      Which, if my routing table is up-to-date *and* connectivity
> (meaning, layer 1 and 2 conditions) is fine up to that node, then I'll
> get a reply.
OLSR.org sets an additional routing table entry for EACH other node of the 
network pointing towards the next hop.

> My point is: what if I get a Host Unreachable reply? Is
> it because:
>
> 1) The node really isnt in the network - that IP is not used.
If the node is not in the network you will have no local route to this node, 
so your node starts to send an ARP (tries to discover the unknown node in your 
neighborhood) and responds with an error

> 2) The node is in the network, but since it may have gotten too dense
> (which is OLSR's supposed especialty), there's a route convergence
> time for that route to get up-to-date.
If you have not got a TC (topology control) packet mentioning the new node, 
your local node does not know about it, so you have no local route for it.

> 3) The node is in the network, but due to some intermittent condition
> (bad wheather, interference, whatever), I cant reach it right now.
If you have a local route your node will try to forward the packet to the next 
hop... if it's get lost because of the condition, it's similar to a packet 
loss on a singlehop WLAN link.


Henning Rogge

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