[c-nsp] understanding ttcp test results
Martin T
m4rtntns at gmail.com
Sat Nov 9 13:30:05 EST 2013
Hi,
I ran a ttcp session with exactly the same parameters between two
Cisco routers in both directions at the same time over a GRE tunnel.
TCP receive window was forced to 65535 bytes because of high bandwidth
delay product on the link. Topology was very simple:
r1[Fa0/0] <-> [Fa0/0]r2
"r1" had IP address 10.255.255.1 and "r2" had IP address 10.255.255.2.
While I expected equal throughput, for some reason, I was able to send
from "r1" to "r2" at 146 kB/s but from "r2" to "r1" only at 46 kB/s.
What puzzled me the most, was the graph of the "r1" F0/0 port which
received high amount of packets, but at the same time, low amount of
traffic: http://s8.postimg.org/f4bwrhjv9/traffic_pattern.png Test
period is between the dotted red lines.
In addition, test details can be seen below:
10.255.255.2 TCP port 63219 -> 10.255.255.1 TCP port 5001:
r1#ttcp
transmit or receive [receive]:
perform tcp half close [n]:
receive buflen [8192]: 81920
bufalign [16384]:
bufoffset [0]:
port [5001]:
sinkmode [y]:
rcvwndsize [4128]: 65535
delayed ACK [y]: n
show tcp information at end [n]: y
ttcp-r: buflen=81920, align=16384/0, port=5001
rcvwndsize=65535, delayedack=no tcp
ttcp-r: accept from 10.255.255.2 (mss 1428, sndwnd 4128, rcvwnd 65535)
ttcp-r: 167772160 bytes in 3426748 ms (3426.748 real seconds) (~46 kB/s) +++
ttcp-r: 95274 I/O calls
ttcp-r: 0 sleeps (0 ms total) (0 ms average)
Connection state is CLOSEWAIT, I/O status: 7, unread input bytes: 0
Connection is ECN Disabled, Mininum incoming TTL 0, Outgoing TTL 255
Local host: 10.255.255.1, Local port: 5001
Foreign host: 10.255.255.2, Foreign port: 63219
Enqueued packets for retransmit: 0, input: 0 mis-ordered: 0 (0 bytes)
Event Timers (current time is 0x6646714):
Timer Starts Wakeups Next
Retrans 1 0 0x0
TimeWait 0 0 0x0
AckHold 0 0 0x0
SendWnd 0 0 0x0
KeepAlive 31950 0 0x6655050
GiveUp 0 0 0x0
PmtuAger 0 0 0x0
DeadWait 0 0 0x0
iss: 2585270323 snduna: 2585270324 sndnxt: 2585270324 sndwnd: 4128
irs: 2772193225 rcvnxt: 2939965387 rcvwnd: 65011 delrcvwnd: 524
SRTT: 38 ms, RTTO: 1842 ms, RTV: 1804 ms, KRTT: 0 ms
minRTT: 304 ms, maxRTT: 304 ms, ACK hold: 200 ms
Flags: passive open, retransmission timeout, gen tcbs, no delayed ACK
win-scale
IP Precedence value : 0
Datagrams (max data segment is 1428 bytes):
Rcvd: 150760 (out of order: 23429), with data: 118784, total data
bytes: 167772160
Sent: 267487 (retransmit: 0, fastretransmit: 0, partialack: 0, Second
Congestion: 0), with data: 0, total data bytes: 0
r1#
r2#ttcp
transmit or receive [receive]: transmit
Target IP address: 10.255.255.1
perform tcp half close [n]:
send buflen [8192]: 81920
send nbuf [2048]:
bufalign [16384]:
bufoffset [0]:
port [5001]:
sinkmode [y]:
buffering on writes [y]:
show tcp information at end [n]: y
ttcp-t: buflen=81920, nbuf=2048, align=16384/0, port=5001 tcp -> 10.255.255.1
ttcp-t: connect (mss 1428, sndwnd 65535, rcvwnd 4128)
ttcp-t: 167772160 bytes in 3426380 ms (3426.380 real seconds) (~46 kB/s) +++
ttcp-t: 2048 I/O calls
ttcp-t: 0 sleeps (0 ms total) (0 ms average)
Connection state is ESTAB, I/O status: 1, unread input bytes: 0
Connection is ECN Disabled, Mininum incoming TTL 0, Outgoing TTL 255
Local host: 10.255.255.2, Local port: 63219
Foreign host: 10.255.255.1, Foreign port: 5001
Connection tableid (VRF): 0
Enqueued packets for retransmit: 20, input: 0 mis-ordered: 0 (0 bytes)
Event Timers (current time is 0xB53BDB418):
Timer Starts Wakeups Next
Retrans 123212 68 0xB53BDB427
TimeWait 0 0 0x0
AckHold 0 0 0x0
SendWnd 0 0 0x0
KeepAlive 0 0 0x0
GiveUp 0 0 0x0
PmtuAger 0 0 0x0
DeadWait 0 0 0x0
Linger 0 0 0x0
ProcessQ 0 0 0x0
iss: 2772193225 snduna: 2939937730 sndnxt: 2939965386 sndwnd: 65535
irs: 2585270323 rcvnxt: 2585270324 rcvwnd: 4128 delrcvwnd: 0
SRTT: 312 ms, RTTO: 327 ms, RTV: 15 ms, KRTT: 0 ms
minRTT: 300 ms, maxRTT: 456 ms, ACK hold: 200 ms
Status Flags: active open
Option Flags: win-scale, 0x400000
IP Precedence value : 0
Datagrams (max data segment is 1428 bytes):
Rcvd: 267447 (out of order: 0), with data: 0, total data bytes: 0
Sent: 150691 (retransmit: 68, fastretransmit: 31905, partialack:
27822, Second Congestion: 7), with data: 150689, total data bytes:
212850400
Packets received in fast path: 0, fast processed: 0, slow path: 0
Packets send in fast path: 0
fast lock acquisition failures: 0, slow path: 0
r2#
10.255.255.1 port 59946 -> 10.255.255.2 port 5002:
r2#ttcp
transmit or receive [receive]:
perform tcp half close [n]:
receive buflen [8192]: 81920
bufalign [16384]:
bufoffset [0]:
port [5001]: 5002
sinkmode [y]:
rcvwndsize [4128]: 65535
delayed ACK [y]: n
show tcp information at end [n]: y
ttcp-r: buflen=81920, align=16384/0, port=5002
rcvwndsize=65535, delayedack=no tcp
ttcp-r: accept from 10.255.255.1 (mss 1428, sndwnd 4128, rcvwnd 65535)
ttcp-r: 167772160 bytes in 1113272 ms (1113.272 real seconds) (~146 kB/s) +++
ttcp-r: 69266 I/O calls
ttcp-r: 0 sleeps (0 ms total) (0 ms average)
Connection state is CLOSEWAIT, I/O status: 7, unread input bytes: 0
Connection is ECN Disabled, Mininum incoming TTL 0, Outgoing TTL 255
Local host: 10.255.255.2, Local port: 5002
Foreign host: 10.255.255.1, Foreign port: 59946
Connection tableid (VRF): 0
Enqueued packets for retransmit: 0, input: 0 mis-ordered: 0 (0 bytes)
Event Timers (current time is 0xB539B8A90):
Timer Starts Wakeups Next
Retrans 1 0 0x0
TimeWait 0 0 0x0
AckHold 0 0 0x0
SendWnd 0 0 0x0
KeepAlive 0 0 0x0
GiveUp 0 0 0x0
PmtuAger 0 0 0x0
DeadWait 0 0 0x0
Linger 0 0 0x0
ProcessQ 0 0 0x0
iss: 563764759 snduna: 563764760 sndnxt: 563764760 sndwnd: 4128
irs: 2193111013 rcvnxt: 2360883175 rcvwnd: 57871 delrcvwnd: 7664
SRTT: 38 ms, RTTO: 1846 ms, RTV: 1808 ms, KRTT: 0 ms
minRTT: 308 ms, maxRTT: 308 ms, ACK hold: 200 ms
Status Flags: passive open, gen tcbs
Option Flags: no delayed ACK, win-scale, 0x400000
IP Precedence value : 0
Datagrams (max data segment is 1428 bytes):
Rcvd: 119267 (out of order: 0), with data: 118784, total data bytes: 167772160
Sent: 235997 (retransmit: 0, fastretransmit: 0, partialack: 0, Second
Congestion: 0), with data: 0, total data bytes: 0
Packets received in fast path: 0, fast processed: 0, slow path: 0
Packets send in fast path: 0
fast lock acquisition failures: 0, slow path: 0
r2#
r1#ttcp
transmit or receive [receive]: transmit
Target IP address: 10.255.255.2
perform tcp half close [n]:
send buflen [8192]: 81920
send nbuf [2048]:
bufalign [16384]:
bufoffset [0]:
port [5001]: 5002
sinkmode [y]:
buffering on writes [y]:
show tcp information at end [n]: y
ttcp-t: buflen=81920, nbuf=2048, align=16384/0, port=5002 tcp -> 10.255.255.2
ttcp-t: connect (mss 1428, sndwnd 65535, rcvwnd 4128)
ttcp-t: 167772160 bytes in 1113380 ms (1113.380 real seconds) (~146 kB/s) +++
ttcp-t: 2048 I/O calls
ttcp-t: 0 sleeps (0 ms total) (0 ms average)
Connection state is ESTAB, I/O status: 1, unread input bytes: 0
Connection is ECN Disabled, Mininum incoming TTL 0, Outgoing TTL 255
Local host: 10.255.255.1, Local port: 59946
Foreign host: 10.255.255.2, Foreign port: 5002
Enqueued packets for retransmit: 24, input: 0 mis-ordered: 0 (0 bytes)
Event Timers (current time is 0x6423B54):
Timer Starts Wakeups Next
Retrans 109420 445 0x6423B8F
TimeWait 0 0 0x0
AckHold 0 0 0x0
SendWnd 0 0 0x0
KeepAlive 0 0 0x0
GiveUp 0 0 0x0
PmtuAger 0 0 0x0
DeadWait 0 0 0x0
iss: 2193111013 snduna: 2360849806 sndnxt: 2360883174 sndwnd: 62679
irs: 563764759 rcvnxt: 563764760 rcvwnd: 4128 delrcvwnd: 0
SRTT: 349 ms, RTTO: 403 ms, RTV: 54 ms, KRTT: 0 ms
minRTT: 300 ms, maxRTT: 424 ms, ACK hold: 200 ms
Flags: active open, retransmission timeout, win-scale
IP Precedence value : 0
Datagrams (max data segment is 1428 bytes):
Rcvd: 235951 (out of order: 0), with data: 0, total data bytes: 0
Sent: 118821 (retransmit: 445, fastretransmit: 35, partialack: 30,
Second Congestion: 0), with data: 118819, total data bytes: 167822140
r1#
Bandwidth of the circuit is 4Mbps. Any ideas why test results were not
around 1.4Mbps in both directions? What could explain this traffic
pattern seen on the graph?
regards,
Martin
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