[OLSR-users] Host vs. Network route propagation with OLSR

[Val Schmidt]

Hello,

I'm new to OLSR and am finding the learning curve steep. I'd like to  
make several comments to clarify things in my mind and I'd be  
terribly grateful to hear your comments and corrections.

It appears to me that there is a huge misconception between the  
designers of OLSR and much of the current user base (myself included,  
actually maybe I'm the only one with the misconception).

As best I can tell, OLSR is fundamentally different than OSPF or RIP  
in that it propagates routes for HOSTS rather than networks - by  
default. I suppose this makes sense as many ad-hoc mesh networks may  
be comprised of "sensor nodes" in which each node both "does  
something" (measures the temperature maybe) and is also a router.  In  
this way, each sensor is a possible path for data transmission, and  
since each node is a router, one need only route directly to  
interfaces and not to networks.

However, this is very different from the model that many people are  
used to in which an ad-hoc mesh of nodes provide routing services  
between networks to which other clients can connect. For example, a  
community wireless project in which each node in a network provides  
both a local AP functionality for client computers and a wireless  
link to other nodes. In this scenario OLSR might be chosen so that  
non-persistent nodes installed on busses or ferries or whatever are  
handled gracefully.  Here, OLSR is meant to provide routing between  
NETWORKS rather than just the network interfaces of the node. This is  
much more like a mobile meshed LAN providing dynamic networking for  
client machines rather than a mesh sensor network.

When you set up OLSR and configure the "interfaces" entry in  
olrsd.conf, you propagate routes to those interfaces through the  
network. But you don't propagate routes to the networks those  
interfaces are attached to, and so clients on those networks are  
unreachable. This fact was and is very confusing to me, as a very  
similar entry in ospfd.conf will propagate routes to the networks  
those interfaces are connected to, rather than just the interface  
itself.  A review of this list archives seems to show that it is  
confusing to many others too.

I'm probably missing something, but I cannot see a reason why an  
"interface" entry in olrsd.conf should not simply propagate a network  
address rather than a host address. It seems to me the more general  
case of a network address would serve to provide a route to both the  
network interface and other addresses on that network - in much the  
same way as other common routing protocols.

Thanks for listening - this wasn't meant to be a rant. I look forward  
to your comments.

-Val




------------------------------------------------------
Val Schmidt
CCOM/JHC
University of New Hampshire
Chase Ocean Engineering Lab
24 Colovos Road
Durham, NH 03824
e: vschmidt [AT] ccom.unh.edu
m: 614.286.3726


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