2008/11/6 Egemen Cetinkaya <egemen.cetink...@gmail.com>
> Hi,
> I am trying to simulate a scenario which brings down a PointToPoint
> link between a node pair. The topology consists of three nodes, no
> loop, and using GlobalRoute manager to route OnOff traffic. To
> accomplish this we used Ipv4::SetDown and Ipv4::SetUp procedures.
> It looks like setting down and setting up the IPv4 interfaces (of the
> source node and the hop node) are working fine. Although, I am
> observing that after setting the "interfaces up", the source does not
> able to send the packets. Below is the portion in the logs I think as
> problematic:
> 1800000000ns Ipv4L3Protocol:SendRealOut(): No route to host. Drop.
> My interpretation of the "Ipv4L3Protocol:SendRealOut(): No route to
> host. Drop." is that:
> A-This can be due to LSAs not being sent on a regular basis (or maybe
> they are being performed without showing anything in the logs). I
> observed in the logs that Link State algorithm do calculations only at
> the beginning of the script. At the end the LS data is cleared due to
> Simulation:Destroy command.
> or
> B-In the ipv4-l3-protocol.cc file it states that (starting line 596):
> " XXX Note here that in most ipv4 stacks in the world, the route
> calculation for an outgoing packet is not done in the ip layer. It is
> done within the application socket when the first packet is sent to
> avoid this costly lookup on a per-packet basis. That would require us
> to get the route from the packet, most likely with a packet tag. The
> higher layers do not do this yet for us. "
> Which I interpret, since there is no IP layer calculation, after the
> interface is brought up, application socket doesn't know how to route
> the packets. (But why, I don't know)
only mentions a possible optimization, to make things faster, not anything
that would change any semantics.
> Now, my first question is what should I do for the source node to be
> able to forward the packets after its interface is setdown and setup?
> I was thinking to reinitialize GlobalRouterManager via a schedule, but
> the script complained about using the PopulateRoutingTables (); since
> it was used previously to initialize/populate routing tables.
> Second question is: do you think not sending LSAs periodically is the
> normal behaviour, or can it be a bug?
up, one of two things normally happen. If the node is a router, the routing
protocol will add the needed IP routing table entries, after a few seconds.
If it is a terminal, the O.S. should automatically trigger a DHCP request,
and the reply would cause a "default gateway" routing table entry to be
added.
Since you are using GlobalRoutingManager, I must say that this is a problem
caused by the way GlobalRoutingManager works, and so GlobalRoutingManager
should be fixed. IMHO, if PopulateRoutingTables cannot be called again in
the middle of the simulation, it is a bug that needs to be fixed. So, file
a bug report in nsnam bug tracker.
While you wait for a bug fix, you can do one of two things: 1. try to fix
the bug yourself ;) or, 2. work around it, i.e. when you bring the network
interface up manually add an appropriate routing table entry.
Regards,
--
Gustavo J. A. M. Carneiro
INESC Porto, Telecommunications and Multimedia Unit
"The universe is always one step beyond logic." -- Frank Herbert
