[OLSR-users] Question about address assignment

[Andreas Tønnesen]

Hi,

You are not the first to ask this question ;-)

OLSR uses the broadcastaddresses that interfaces are pre-configured 
with. So for two nodes to "hear" eachother they need to use the same 
broadcast address which usually means that they must be on the same 
subnet. This is both good and bad. Good in the sense that it allows for 
subnet design within the manet - bad in the way that it is not very 
"ad-hocish". By "ad-hocish" I mean the idea of nodes roaming freely 
entering and exitting MANETS dynamically.

AODV specifies in the RFC that ALL control traffic should be broadcasted 
on 255.255.255.255. When using this broadcast address ALL nodes will 
pick up the traffic. OLSR on the other hand does not specify this. So I 
figured it was best leave both options to the user. As a result you can 
set the IP4BROAD option in the configfile to either auto, which will 
cause OLSRd to use the broadcastaddress fetched from the interface(s), 
or you can set it to 255.255.255.255 which causes all controltraffic to 
be broadcasted on 255.255.255.255, meaning that the addresses of your 
nodes does not have to reside within the same subnet.

I hope this answered your question

regards,
Andreas T

(spam-protected) wrote:
> Greetings,
> 
> The OLSR code seems to be well written and solid.  I have a question
> about assignment of IP addresses and how addresses are handled by
> the UniK OLSR daemon.
> 
> I am running olsrd on Linux machines using an Ethernet interface
> because I currently have no wireless devices.
> 
> Section 11.1 of RFC 3626 says:
> The nodes in the MANET network SHOULD be assigned addresses within a
> defined address sequence, i.e., the nodes in the MANET SHOULD be
> addressable through a network address and a netmask. 
> 
> I understand that this is done to enable us to advertise routes
> from the OLSR MANET into other routing domains, but that it is not
> a requirement.  
> 
> I also understand that generally in a MANET there are no requirements
> as to how addresses are assigned and there may be nodes from different
> "IP subnets" in the same MANET.
> 
> I have the following setup:
> 
>          Linux        Eth          Linux
>         -------      switch       -------
>         |     |      -----        |     |
>         |  X  |______|   |________|  Y  |
>         |     |      |   |        |     |
>         -------      -----        -------
> 
> When workstations X and Y are on the same IP subnet (192.168.77.0), 
> OLSR works fine.  When they are on differing subnets (X = 192.168.87.0
> Y = 192.168.97.0) OLSR doesn't work at all.
> 
> Is this because of the way olsrd is implemented or is it due to the
> way routing works on Linux, or is my understanding incorrect?
> 
> Thanks for any help you can give.
> 
> Richard Herron
> L-3 Communications
> 
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> (spam-protected)
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-- 
Andreas Tønnesen((spam-protected))
UniK University Graduation Center
University of Oslo
http://www.olsr.org