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    SubjectRe: When does Linux drop UDP packets?
    On Thu, Jun 04, 2009 at 04:53:47PM +0200, Philipp Reh wrote:
    > Dear list,
    > I have the following setting in which a client that resides on the same
    > physical network as a server wants to receive any UDP packet that
    > arrives on any of its interfaces sent by that server.
    > The code sets the broadcast flag, calls bind to INADDR_ANY and
    > uses recvfrom from there on.
    > Let's say the server resides in the subnet and the
    > client in The server uses its real IP as the packet's
    > sender ip (

    You don't say what the client IP is. Let's assume that it is
    for simplicity.

    > Now the first problem I've encountered is the following:
    > If the client removes its default route and doesn't have any route
    > pointing into the subnet the server is in, the packets get discarded
    > (still tcpdump sees them).

    Are you saying that the server sent to with source ip of and the client did not see it?

    > The second problem is that if the server uses the broadcast address as
    > its sender address (, the packets get always discarded
    > (again, tcpdump sees them).

    Again, what was the destination IP address?

    > Now if the server fakes its sender address to be in the client's subnet,
    > every packet arrives again.

    So the only thing you change is the sender address?

    What tools are you using to read the packets, and how do you know it is

    -- Steve

    > So my real question is:
    > When does Linux discard packets and how can I prevent it from doing
    > that?

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      Last update: 2009-06-04 18:01    [W:0.040 / U:41.956 seconds]
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