[Ns-bugs] [Bug 400] Wifi Muti-Hop Network not forwaring packets (atleast ARP)

[code@nsnam.ece.gatech.edu]

http://www.nsnam.org/bugzilla/show_bug.cgi?id=400





--- Comment #3 from Luis <cortes at gatech.edu>  2008-11-05 09:58:24 EDT ---
(In reply to comment #1)
> (In reply to comment #0)
> > Created an attachment (id=289)
 --> (http://www.nsnam.org/bugzilla/attachment.cgi?id=289) [details] [details]
> > Test script were ns3 fails
> > 
> > Hi,
> > 
> > I am using ns3.2.1.RC2 and I cant setup a multi-hop network as follows:
> > 
> > TOPOLOGY:
> > 
> >      WIRED CSMA             WIRELESS CHANNEL
> >    ______________
> >    O            O  ))          (( O ))           (( O
> >    N3           N0                N1                N2  
> > 
> > Here N1 hears packets from N2 and N0 but N2 can not communicate directly with
> > N0. However, when I run it, N2 sends his ARP but N1 does not forward it to N0
> > and therefore it is not able to communicate. I am using Global Routing and
> > running OLSR on the wireless network. 
> 
> Yes, this will not work.  Proxy ARP is not supported, there is one subnet for
> the entire adhoc network, and N2 assumes that everyone on the subnet is
> reachable via one hop (and therefore ARPs for it).
> 
> If you configure a real network like this, you would run into the same problem,
> due to the assumption that link and subnet are synonymous, but they are not in
> this case.
> 

Really? I implemented a wireless mesh network before using olsrd
(http://www.olsr.org/) and B.A.T.M.A.N. (https://www.open-mesh.net/batman)
routing protocols. It was composed of a few laptops running on Adhoc mode, on
ubuntu OS. There was one gateway (N0) to the internet (N3), two wireless
routers (adhoc nodes) (N1) and an Access Point (N2). I do remember seeing an
ARP originating from the AP (N2). I do not remember, however, what happened at
N1, how was the packet forwarded to N0. 



> > 
> > P.S. Is there anyway to have a GOD mode ARP in which everybody knows everybody
> > else's MAC address? If not, can you guys add this feature? Its probably easy to
> > do but will take me longer to do than you guys.
> 
> But, you do not want N0's MAC address here because N2 cannot reach N0 anyway.
> 
> One solution would be to put /32 addresses on each wireless interface, but I
> haven't tested that.  That, if OLSR could handle it, would eliminate the ARPing
> for N0.  It would require some low-level configuration (probably not through
> the helpers).

I think this is what happened in my Wireless Mesh Network implementation. So
each Node had its next hop be its default gateway to the internet. Here is my
global routing table for 3 hops:

FROM\TO         10.0.0.1,       10.0.0.2,       10.0.0.6,       10.0.0.100
10.0.0.1;       0,              10.0.0.2,       10.0.0.2,       10.0.0.2
10.0.0.2;       10.0.0.1,       10.0.0.1,       10.0.0.6,       10.0.0.6
10.0.0.6;       10.0.0.2,       10.0.0.2,       10.0.0.2,       10.0.0.100
10.0.0.100;     10.0.0.6,       10.0.0.6,       10.0.0.6,       10.0.0.6


The first column shows FROM which IP, the first row shows TO which IP. The IP
listed under a FROM to a TO is the Next hop, and the IP listed under a FROM to
the same TO is the Default Gateway. So from 10.0.0.2 to 10.0.0.100, the next
hop is 10.0.0.6. And the default gateway for 10.0.0.2 is 10.0.0.1 (looking at
>From 10.0.0.2 To 10.0.0.2).

The topology was:

Internet             WIRELESS CHANNEL
_______
      O  ))          (( O ))           (( O ))           (( O ))
      N1                N2                N6               N100

where N1 the gateway, N2 and N6 wireless nodes, and N100 was the AP. Is there
no default gateway implementation on NS3? I'm going to try to setup the IP's
Manually.

> 
> I think the answer is to work on a routing solution to this-- I will try to
> look at it more tomorrow.
> 

I think Multi-hop wireless networks are important to the research community and
its very important that NS3 has such capability. 

Thanks,


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