03-07-2013
Tcpdump -i any producing duplicate packages?
Hi,
Can anyone explain why do I see same request twice in tcpdump package when I use "tcpdump -i any"?
So I'm tracing packets on eth1.800 interface, but using "tcpdump -i any" to capture them. What I see is that the requests/responses from my side seem to appear as duplicate in the pcap file, but the incoming requests/responses are just single packets.
If I do "tcpdump -i eth1.800", both outgoing and incoming requests/responses are single packets.
I tried to google this and found some similar posts, but there was no explanation why this happens.
Thanks!
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LEARN ABOUT FREEBSD
ipresend
IPRESEND(1) General Commands Manual IPRESEND(1)
NAME
ipresend - resend IP packets out to network
SYNOPSIS
ipresend [ -EHPRSTX ] [ -d <device> ] [ -g <gateway> ] [ -m <MTU> ] [ -r <filename> ]
DESCRIPTION
ipresend was designed to allow packets to be resent, once captured, back out onto the network for use in testing. ipresend supports a num-
ber of different file formats as input, including saved snoop/tcpdump binary data.
OPTIONS
-d <interface>
Set the interface name to be the name supplied. This is useful with the -P, -S, -T and -E options, where it is not otherwise possi-
ble to associate a packet with an interface. Normal "text packets" can override this setting.
-g <gateway>
Specify the hostname of the gateway through which to route packets. This is required whenever the destination host isn't directly
attached to the same network as the host from which you're sending.
-m <MTU>
Specify the MTU to be used when sending out packets. This option allows you to set a fake MTU, allowing the simulation of network
interfaces with small MTU's without setting them so.
-r <filename>
Specify the filename from which to take input. Default is stdin.
-E The input file is to be text output from etherfind. The text formats which are currently supported are those which result from the
following etherfind option combinations:
etherfind -n
etherfind -n -t
-H The input file is to be hex digits, representing the binary makeup of the packet. No length correction is made, if an incorrect
length is put in the IP header.
-P The input file specified by -i is a binary file produced using libpcap (i.e., tcpdump version 3). Packets are read from this file
as being input (for rule purposes).
-R When sending packets out, send them out "raw" (the way they came in). The only real significance here is that it will expect the
link layer (i.e. ethernet) headers to be prepended to the IP packet being output.
-S The input file is to be in "snoop" format (see RFC 1761). Packets are read from this file and used as input from any interface.
This is perhaps the most useful input type, currently.
-T The input file is to be text output from tcpdump. The text formats which are currently supported are those which result from the
following tcpdump option combinations:
tcpdump -n
tcpdump -nq
tcpdump -nqt
tcpdump -nqtt
tcpdump -nqte
-X The input file is composed of text descriptions of IP packets.
SEE ALSO
snoop(1m), tcpdump(8), etherfind(8c), ipftest(1), ipresend(1), iptest(1), bpf(4), dlpi(7p)
DIAGNOSTICS
Needs to be run as root.
BUGS
Not all of the input formats are sufficiently capable of introducing a wide enough variety of packets for them to be all useful in testing.
If you find any, please send email to me at darrenr@pobox.com
IPRESEND(1)