Cheap way to detect client round trip times for http
$tcpinfo_rtt, $tcpinfo_rttvar, $tcpinfo_snd_cwnd, $tcpinfo_rcv_space
information about the client TCP connection; available on systems that support the TCP_INFO socket option
http://nginx.org/en/docs/http/ngx_http_core_module.html#variables
If you have access to a linux or unix machine1, you should use tcptrace. All you need to do is capture the client traffic with wireshark or tcpdump to a pcap file.
After you have that .pcap file2, analyze with tcptrace -xtraffic <pcap_filename>3. This will generate two text files, and the average RTT stats for all connections in that pcap are shown at the bottom of the one called traffic_stats.dat.
[mpenning@Bucksnort tcpperf]$ tcptrace -xtraffic willers.pcap
mod_traffic: characterizing traffic
1 arg remaining, starting with 'willers.pcap'
Ostermann's tcptrace -- version 6.6.1 -- Wed Nov 19, 2003
16522 packets seen, 16522 TCP packets traced
elapsed wallclock time: 0:00:00.200709, 82318 pkts/sec analyzed
trace file elapsed time: 0:03:21.754962
Dumping port statistics into file traffic_byport.dat
Dumping overall statistics into file traffic_stats.dat
Plotting performed at 15.000 second intervals
[mpenning@Bucksnort tcpperf]$
[mpenning@Bucksnort tcpperf]$ cat traffic_stats.dat
Overall Statistics over 201 seconds (0:03:21.754962):
4135308 ttl bytes sent, 20573.672 bytes/second
4135308 ttl non-rexmit bytes sent, 20573.672 bytes/second
0 ttl rexmit bytes sent, 0.000 bytes/second
16522 packets sent, 82.199 packets/second
200 connections opened, 0.995 conns/second
11 dupacks sent, 0.055 dupacks/second
0 rexmits sent, 0.000 rexmits/second
average RTT: 67.511 msecs <------------------
[mpenning@Bucksnort tcpperf]$
The .pcap file used in this example was a capture I generated when I looped through an expect script that pulled data from one of my servers. This was how I generated the loop...
#!/usr/bin/python
from subprocess import Popen, PIPE
import time
for ii in xrange(0,200):
# willers.exp is an expect script
Popen(['./willers.exp'], stdin=PIPE, stdout=PIPE, stderr=PIPE)
time.sleep(1)
END NOTES:
- A Knoppix Live-CD will do
- Filtered to only capture test traffic
-
tcptraceis capable of very detailed per-socket stats if you use other options...
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[mpenning@Bucksnort tcpperf]$ tcptrace -lr willers.pcap
1 arg remaining, starting with 'willers.pcap'
Ostermann's tcptrace -- version 6.6.1 -- Wed Nov 19, 2003
16522 packets seen, 16522 TCP packets traced
elapsed wallclock time: 0:00:00.080496, 205252 pkts/sec analyzed
trace file elapsed time: 0:03:21.754962
TCP connection info:
200 TCP connections traced:
TCP connection 1:
host c: myhost.local:44781
host d: willers.local:22
complete conn: RESET (SYNs: 2) (FINs: 1)
first packet: Tue May 31 22:52:24.154801 2011
last packet: Tue May 31 22:52:25.668430 2011
elapsed time: 0:00:01.513628
total packets: 73
filename: willers.pcap
c->d: d->c:
total packets: 34 total packets: 39
resets sent: 4 resets sent: 0
ack pkts sent: 29 ack pkts sent: 39
pure acks sent: 11 pure acks sent: 2
sack pkts sent: 0 sack pkts sent: 0
dsack pkts sent: 0 dsack pkts sent: 0
max sack blks/ack: 0 max sack blks/ack: 0
unique bytes sent: 2512 unique bytes sent: 14336
actual data pkts: 17 actual data pkts: 36
actual data bytes: 2512 actual data bytes: 14336
rexmt data pkts: 0 rexmt data pkts: 0
rexmt data bytes: 0 rexmt data bytes: 0
zwnd probe pkts: 0 zwnd probe pkts: 0
zwnd probe bytes: 0 zwnd probe bytes: 0
outoforder pkts: 0 outoforder pkts: 0
pushed data pkts: 17 pushed data pkts: 33
SYN/FIN pkts sent: 1/1 SYN/FIN pkts sent: 1/0
req 1323 ws/ts: Y/Y req 1323 ws/ts: Y/Y
adv wind scale: 6 adv wind scale: 1
req sack: Y req sack: Y
sacks sent: 0 sacks sent: 0
urgent data pkts: 0 pkts urgent data pkts: 0 pkts
urgent data bytes: 0 bytes urgent data bytes: 0 bytes
mss requested: 1460 bytes mss requested: 1460 bytes
max segm size: 792 bytes max segm size: 1448 bytes
min segm size: 16 bytes min segm size: 32 bytes
avg segm size: 147 bytes avg segm size: 398 bytes
max win adv: 40832 bytes max win adv: 66608 bytes
min win adv: 5888 bytes min win adv: 66608 bytes
zero win adv: 0 times zero win adv: 0 times
avg win adv: 14035 bytes avg win adv: 66608 bytes
initial window: 32 bytes initial window: 40 bytes
initial window: 1 pkts initial window: 1 pkts
ttl stream length: 2512 bytes ttl stream length: NA
missed data: 0 bytes missed data: NA
truncated data: 0 bytes truncated data: 0 bytes
truncated packets: 0 pkts truncated packets: 0 pkts
data xmit time: 1.181 secs data xmit time: 1.236 secs
idletime max: 196.9 ms idletime max: 196.9 ms
throughput: 1660 Bps throughput: 9471 Bps
RTT samples: 18 RTT samples: 24
RTT min: 43.8 ms RTT min: 0.0 ms
RTT max: 142.5 ms RTT max: 7.2 ms
RTT avg: 68.5 ms RTT avg: 0.7 ms
RTT stdev: 35.8 ms RTT stdev: 1.6 ms
RTT from 3WHS: 80.8 ms RTT from 3WHS: 0.0 ms
RTT full_sz smpls: 1 RTT full_sz smpls: 3
RTT full_sz min: 142.5 ms RTT full_sz min: 0.0 ms
RTT full_sz max: 142.5 ms RTT full_sz max: 0.0 ms
RTT full_sz avg: 142.5 ms RTT full_sz avg: 0.0 ms
RTT full_sz stdev: 0.0 ms RTT full_sz stdev: 0.0 ms
post-loss acks: 0 post-loss acks: 0
segs cum acked: 0 segs cum acked: 9
duplicate acks: 0 duplicate acks: 1
triple dupacks: 0 triple dupacks: 0
max # retrans: 0 max # retrans: 0
min retr time: 0.0 ms min retr time: 0.0 ms
max retr time: 0.0 ms max retr time: 0.0 ms
avg retr time: 0.0 ms avg retr time: 0.0 ms
sdv retr time: 0.0 ms sdv retr time: 0.0 ms
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