[Click] packets not seen by click unless tcpdump running

[Eddie Kohler]

Hi Marcel,

1. Your first problem sounds like you didn't set FromDevice's PROMISC 
argument to true.  Without PROMISC true, the FromDevice is not acting 
as a sniffer; it's just reporting packets sent to *this* host.

2. Queues maximize utilization.  You place a Queue anywhere you have a 
bursty input process, where you might need storage to absorb a burst.  
For example, say you have a FromDevice that can generate up to 300 
packets/sec, and a ToDevice that can send at most 250 packets/sec.  
Then you want to place a Queue in between, so that if the FromDevice 
generates a burst, no packets are dropped.  In concrete terms, you 
place it on the boundary between push elements and pull elements.

Eddie


On Oct 14, 2004, at 12:27 PM, Marcel Poisot wrote:
> I have the following configuration, run in User mode:
>
> FromDevice( eth0 ) -> ToDump( input.dump ) -> /* uninteresting stuff */
>
> I have Iptables set to drop packets from INPUT, and accept all packets
> from FORWARD and OUTPUT.  I do this because I just want to passively
> record packets right now, and I don't want the OS sending out RST or 
> any
> programs actually responding to packets.
>
> With this router running, I try to telnet to this machine from a second
> machine, expecting input.dump to record the several SYN packets issued
> by telnet trying to initiate the connection.  I have tcpdump running on
> the second machine so I see the three SYN packets go out.
>
> However, input.dump only records the first SYN packet.  Sometimes I see
> other traffic, such as ARP requests and NetBios broadcasts from other
> machines on the network.
>
> Strangely, if I run tcpdump at the same time as the click router, then
> input.dump DOES record all the traffic I think it should be getting 
> (ie,
> the three SYN packets)!  What is going on here?  Why does the click
> router not receive traffic unless tcpdump is running?
>
>
>
> 2.
>
> What is the proper/required use of Queue?  Is it needed for Userland
> click configurations, or just Kernel mode?  Where in a configuration
> should I put them, and how many are needed?  (I really don't want any
> packets dropped).  Could this have anything to do with my problem 
> above?
>
>
> Thanks,
> Marcel
>
>
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