I used the -R and -K option but it doesnt seem to be working as I captured the pumped traffic using tcpdump and the number of packets that I see there dont seem to match the number of packets that I expect in the time frame.
First of all make sure you are using the latest version, available here. You will want to use the -K and --mbps (or -M) options, for example:
# tcpreplay -i eth7 -K --mbps 1000 smallFlows.pcap
File Cache is enabled
Actual: 14261 packets (9216531 bytes) sent in 0.073761 seconds.
Rated: 124951275.0 Bps, 999.61 Mbps, 193340.65 pps
Flows: 1209 flows, 16390.77 fps, 14243 flow packets, 18 non-flow
Statistics for network device: eth7
Attempted packets: 14261
Successful packets: 14261
Failed packets: 0
Truncated packets: 0
Retried packets (ENOBUFS): 0
Retried packets (EAGAIN): 0
When you attempt to move to higher speeds (e.g. 10GigE) you may need to generate a bigger block of data by using the --loop option. Also with Tcpreplay version 4.0 there are the more advanced --netmap and --unique-ip options which on a properly set up system, will achieve near wire rate and very high flows/sec. More information available at Tcpreplay How To. Here is an example:
# tcpreplay -i eth7 -K --mbps 9500 --loop 100 --netmap --unique-ip smallFlows.pcap
Switching network driver for eth7 to netmap bypass mode... done!
File Cache is enabled
Actual: 1426100 packets (921653100 bytes) sent in 0.776133 seconds.
Rated: 1187493767.1 Bps, 9499.95 Mbps, 1837442.80 pps
Flows: 120900 flows, 155772.27 fps, 1424300 flow packets, 1800 non-flow
Statistics for network device: eth7
Attempted packets: 1426100
Successful packets: 1426100
Failed packets: 0
Truncated packets: 0
Retried packets (ENOBUFS): 0
Retried packets (EAGAIN): 0
Switching network driver for eth7 to normal mode... done!