[OLSR-users] When does a node use ARP?

Dan Flett (spam-protected)
Sat Jul 8 17:16:55 CEST 2006

Hi all,

I have a question regarding priorities in routing tables and ARP.

I understand that in a routing table, where entries have overlapping
netmasks, the narrower netmask has priority.  This is often the case with
OLSR where nodes advertise themselves as /32 routes by default, and their
network interfaces have wide netmasks - such as /8 or /16.

I am wondering - can an OLSR node communicate with a one-hop non-OLSR node
if there is a HNA present with a netmask that overlaps the non-OLSR node?

Consider this scenario:
Node A has a wireless interface with the IP address and is
running OLSR

Node Z is running OLSR and is injecting a HNA of onto the
network and is many hops away from Node A

Node B is has a wireless interface with the IP address of and
is within radio range (and therefore Ethernet range), of Node A but does not
run OLSR.

My question is - If Node A, with an empty ARP cache, attempts to communicate
with Node B - what happens?  Normally Node A would send an ARP broadcast and
Node B would answer it.  But does the /17 HNA from Node Z interfere with
this?  Would Node A consult it's routing table and decide that the traffic
should go via Node Z, unaware that Node B is within direct Ethernet range?



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