From Thomas McMurphy:

Version information (output of -V)
tcpreplay version: 4.0.3 (build git:v4.0.3)
Copyright 2013-2014 by Fred Klassen -
AppNeta Inc.
Copyright 2000-2012 by Aaron Turner
The entire Tcpreplay Suite is licensed under the GPLv3
Cache file supported: 04
Not compiled with libdnet.
Compiled against libpcap: 1.5.3
64 bit packet counters: enabled
Verbose printing via tcpdump: enabled
Packet editing: disabled
Fragroute engine: disabled
Injection method: PF_PACKET send()

Platform (Red Hat Linux 9 on Intel, Solaris 7 on SPARC, etc)
Debian 3.11.8-1

Make & model of the network card(s) and driver(s) version
Card: Intel Corporation Ethernet 10G 2P X520 Adapter (rev 01)
Driver: ixgbe 3.18.7

If possible, attach the pcap file used (compressed with bzip2 or gzip preferred)
bigFlows.pcap from http://tcpreplay.appneta.com/wiki/captures.html

Detailed description of your problem or what you are trying to accomplish
I have a linux host with two interfaces 'traffic1' and 'traffic2'.
Both of these interfaces are connected to each other through a switch.
With this setup I am trying to test a pcap/cachefile pair for
bidirectional replay.

To create the cachefile I used the following command:
/usr/local/bin/tcpprep --auto=client --pcap=bigFlows.pcap
--cachefile=bigFlows.cache

Then used the following command to replay the file one time:
/usr/local/bin/tcpreplay --loop=1 --quiet --topspeed
--cachefile=bigFlows.cache --intf1=traffic1 --intf2=traffic2
bigFlows.pcap

And received the following report:
Actual: 791615 packets (355417784 bytes) sent in 0.602658 seconds.
Rated: 589750379.1 Bps, 4718.00 Mbps, 1313539.35 pps
Flows: 40686 flows, 67510.92 fps, 791179 flow packets, 436 non-flow
Statistics for network device: traffic1
Attempted packets: 584308
Successful packets: 584308
Failed packets: 0
Truncated packets: 0
Retried packets (ENOBUFS): 0
Retried packets (EAGAIN): 0
Flows total: 28397
Flows unique: 0
Flows expired: 0
Flow packets: 584308
Non-flow packets: 0
Invalid flow packets: 0
Statistics for network device: traffic2
Attempted packets: 207307
Successful packets: 207307
Failed packets: 0
Truncated packets: 0
Retried packets (ENOBUFS): 0
Retried packets (EAGAIN): 0
Flows total: 12289
Flows unique: 0
Flows expired: 0
Flow packets: 206871
Non-flow packets: 436
Invalid flow packets: 0

After that I ran the following command to replay the file two times:
/usr/local/bin/tcpreplay --loop=2 --quiet --topspeed
--cachefile=bigFlows.cache --intf1=traffic1 --intf2=traffic2
bigFlows.pcap

And received the following report:
Actual: 791615 packets (355417784 bytes) sent in 0.846339 seconds.
Rated: 419947307.1 Bps, 3359.57 Mbps, 935340.33 pps
Flows: 40686 flows, 48072.93 fps, 1582358 flow packets, 872 non-flow
Statistics for network device: traffic1
Attempted packets: 584308
Successful packets: 584308
Failed packets: 0
Truncated packets: 0
Retried packets (ENOBUFS): 0
Retried packets (EAGAIN): 0
Flows total: 28397
Flows unique: 0
Flows expired: 0
Flow packets: 584308
Non-flow packets: 0
Invalid flow packets: 0
Statistics for network device: traffic2
Attempted packets: 207307
Successful packets: 207307
Failed packets: 0
Truncated packets: 0
Retried packets (ENOBUFS): 0
Retried packets (EAGAIN): 0
Flows total: 12289
Flows unique: 0
Flows expired: 0
Flow packets: 206871
Non-flow packets: 436
Invalid flow packets: 0

Now with the second run I was expecting to see twice as many packets
transmitted as the first. To confirm the packet counts are really the
same I reran the tcpreplay commands again with tcpdump running on both
traffic interfaces. For both scenarios, tcpreplay and tcpdump reports
that 791615 packets were seen.

I have tried replaying the file again without the '--intf2' or
'--cachefile' options and I am seeing the packet count values I was
expecting.

/usr/local/bin/tcpreplay --quiet --topspeed --intf1=traffic1 bigFlows.pcap
Actual: 791615 packets (355417784 bytes) sent in 0.749699 seconds.
Rated: 474080643.0 Bps, 3792.64 Mbps, 1055910.43 pps
Flows: 40686 flows, 54269.78 fps, 791179 flow packets, 436 non-flow
Statistics for network device: traffic1
Attempted packets: 791615
Successful packets: 791615
Failed packets: 0
Truncated packets: 0
Retried packets (ENOBUFS): 0
Retried packets (EAGAIN): 0

/usr/local/bin/tcpreplay --loop=2 --quiet --topspeed --intf1=traffic1
bigFlows.pcap
Actual: 1583230 packets (710835568 bytes) sent in 1.04 seconds.
Rated: 481899875.8 Bps, 3855.19 Mbps, 1073326.06 pps
Flows: 40686 flows, 27582.43 fps, 3164716 flow packets, 1744 non-flow
Statistics for network device: traffic1
Attempted packets: 1583230
Successful packets: 1583230
Failed packets: 0
Truncated packets: 0
Retried packets (ENOBUFS): 0
Retried packets (EAGAIN): 0

• Is the behaviour the result of something I've done wrong?
• Anyone got ideas for more tests I can run to narrow down the issue?