[OLSR-users] Question about address assignment

Andreas Tønnesen (spam-protected)
Thu Apr 29 18:21:51 CEST 2004

Hi Richard,

you are ever so right!
On all my tests I have had routes to the networks trough other
interfaces. That must have been why the packets have been sent
up the layers. Sorry about that :)

I'll look more into it tomorrow.

- Andreas

(spam-protected) wrote:
> Andreas,
> I have been looking into the Linux kernel source in
> kernel/net/ipv4/route.c and I think I know what is happening.
> Recall that I have two Linux systems with IP addresses from
> different subnets connected via a switch.  I configured olsrd
> to use as its broadcast address.
>          Linux        Eth          Linux
>         -------      switch       -------
>         |     |      -----        |     |
>         |  X  |______|   |________|  Y  |
>         |     |      |   |        |     |
>         -------      -----        -------
> The code in route.c, the function ip_route_input_slow() checks
> the destination address for 0xffffffff and jumps to the brd_input
> label.  There it calls fib_validate_source() which returns an
> error and the code jumps to the martian_source label.  The packet
> is treated as a Martian packet and dropped because it did not come
> from a source address with a known route.
> Has anyone encountered this before?  Does anyone have suggestions
> for dealing with this besides hacking the kernel?
> Thanks,
> Richard Herron
> L-3 Communications
> -----Original Message-----
> From: Andreas Tønnesen [mailto:(spam-protected)]
> Sent: Thursday, April 22, 2004 9:47 PM
> To: (spam-protected)
> Cc: (spam-protected)
> Subject: Re: [OLSR-users] Question about address assignment
> The UDP packets to should be passed up the stack as far 
> as I know... You are sure there's no netfilter rule stopping the 
> traffic(iptables -F)?
> I will check this out when I get back to the lab!
> - Andreas
> (spam-protected) wrote:
>>I have modified my OLSR config file to set IP4BROAD to 
>> and I have attempted to run my systems with IP
>>addresses from different subnets, but I am still having trouble.
>>I have attached traces from both systems showing the OLSRD debug
>>and some tcpdump printouts.  The tcpdump shows that the Hello
>>messages are being send and seen at the Ethernet interfaces
>>of both machines, but the messages don't seem to be getting to
>>the OLSR protocol.
>>For example:
>>09:49:15.022709 >  udp 20 (DF) [tos
>>09:49:21.000156 >  udp 20 (DF) [tos
>>Could this be because the Linux network stack is filtering out
>>messages that do not originate from the same subnet as the
>>interface that receives them?
>>I would appreciate any ideas you have on this.
>>Thank you,
>>Richard Herron
>>L-3 Communications
>>-----Original Message-----
>>From: Andreas Tønnesen [mailto:(spam-protected)]
>>Sent: Wednesday, April 14, 2004 12:56 AM
>>To: (spam-protected)
>>Cc: (spam-protected)
>>Subject: Re: [OLSR-users] Question about address assignment
>>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 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 which causes all controltraffic to 
>>be broadcasted on, meaning that the addresses of your 
>>nodes does not have to reside within the same subnet.
>>I hope this answered your question
>>Andreas T
>>(spam-protected) wrote:
>>>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 (, 
>>>OLSR works fine.  When they are on differing subnets (X =
>>>Y = 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
>>>olsr-users mailing list


Andreas Tønnesen((spam-protected))
UniK University Graduation Center
University of Oslo

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