tcpdump mailing list archives
Re: question
From: Guy Harris <gharris () sonic net>
Date: Wed, 9 Oct 2002 01:05:57 -0700
On Wed, Oct 09, 2002 at 01:48:24AM -0400, subramoni padmanabhan wrote:
I seem to have a very peculiar problem with the libpcap library. I am using the pcap_loop function to capture any packets with a specific condition set and return to my program. I am using the "any" device. Once I receive packets, I forward them to another machine on a UDP socket. The problem I am having is that when I send the packet out the UDP socket, I think the pcap_loop function is again capturing the packet and returning coz it satisfies the condition.
Well, yes, libpcap *is* supposed to be able to capture packets sent by the machine running the libpcap-based application. The problem is peculiar only in that it's peculiar to your program; most libpcap applications are passive sniffers, and don't have that problem.
This way I get copies of all packets which I try to send out. I, in turn, send these packets out only to be captured again and returned. This goes into an infinite loop until some error occurs and my program exits. How do I go about solving this? any ideas will be greatly appreciated.
It sounds as if you don't care about forwarding packets that the machine on which the application is running sends. If so, then, given that you're capturing on the "any" device, then, as per the libpcap man page, the link-layer header on the packets starts with a network-byte-order "packet type" field, which has the values: 0 packet was sent to us by somebody else 1 packet was broadcast by somebody else 2 packet was multicast, but not broadcast, by somebody else 3 packet was sent by somebody else to somebody else 4 packet was sent by us You could have the application just ignore packets with the value 4, i.e. not forward them. - This is the TCPDUMP workers list. It is archived at http://www.tcpdump.org/lists/workers/index.html To unsubscribe use mailto:tcpdump-workers-request () tcpdump org?body=unsubscribe
Current thread:
- question subramoni padmanabhan (Oct 08)
- Re: question Vishal Malhan` (Oct 09)
- Re: question Guy Harris (Oct 09)
- <Possible follow-ups>
- Re: question subramoni padmanabhan (Oct 09)
- question subramoni padmanabhan (Oct 10)
- question subramoni padmanabhan (Oct 14)
- question subramoni padmanabhan (Oct 15)
- Re: question Guy Harris (Oct 16)