[OLSR-users] Host vs. Network route propagation with OLSR
Thu Jul 20 21:38:44 CEST 2006
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.
University of New Hampshire
Chase Ocean Engineering Lab
24 Colovos Road
Durham, NH 03824
e: vschmidt [AT] ccom.unh.edu
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