Phil,
I do understand that the lower burst (5000) is too low for production
and wouldn't use it. However, I can see that in a 10 second transfer I
can only push about 248Kbytes:
[EMAIL PROTECTED] ~]# iperf -c 10.180.55.211 -P 1 -i 1 -t 10
------------------------------------------------------------
Client connecting to 10.180.55.211, TCP port 5001
TCP window size: 16.0 KByte (default)
------------------------------------------------------------
[ 3] local 192.168.10.2 port 33538 connected with 10.180.55.211 port 5001
[ ID] Interval Transfer Bandwidth
...
0.0-10.1 sec 248 KBytes 200 Kbits/sec
And yet the interface counters show an almost insignificant number of drops
(only 65 packets, although that is out of a total of 253 packets) :
Router#show int fa1/0 rate-limit
FastEthernet1/0
Input
matches: all traffic
params: 10000000 bps, 5000 limit, 5000 extended limit
conformed 188 packets, 260984 bytes; action: transmit
exceeded 65 packets, 97206 bytes; action: drop
last packet: 400ms ago, current burst: 2150 bytes
last cleared 00:00:15 ago, conformed 137000 bps, exceeded 51000 bps
So, that would seem to indicate that the interface did, in fact receive 10mbps
plus some burst. The big trouble is that the packets don't seem to be arriving
at the interface at rate. The "show interface" stats (see
http://users.reachone.com/drsmooth/ShowIntSmallBurst.txt ), taken manually
approximately once per second for the length of the 10 second test. Even after
3 seconds the interface has only received 113 packets input (147514 bytes) which
is nowhere near the CAR of 10mbps.
In addition, SNMP seems to reflect that the interface has not received anything
near the CAR (see http://users.reachone.com/drsmooth/smallburst.jpg ). I have
also monitored the packet counters on the testing client (that sends the bulk
data packets). It shows that after approx 3 seconds only 34,060 bytes in 36
packets, or 10,000bps. (As a frustrating aside, SNMP monitoring box of the
testing client interface actually shows a 5 second average of 1.7mbps with 1
second values near 7mbps).
[EMAIL PROTECTED] ~]# ./showintstats
09.44.691896144
TX packets:221 errors:0 dropped:0 overruns:0 carrier:0
RX bytes:18784 (18.3 KiB) TX bytes:33538 (32.7 KiB)
09.45.702834271
TX packets:221 errors:0 dropped:0 overruns:0 carrier:0
RX bytes:18784 (18.3 KiB) TX bytes:33538 (32.7 KiB)
09.46.713474652
TX packets:257 errors:0 dropped:0 overruns:0 carrier:0
RX bytes:20448 (19.9 KiB) TX bytes:67598 (66.0 KiB)
09.47.725242663
TX packets:257 errors:0 dropped:0 overruns:0 carrier:0
RX bytes:20448 (19.9 KiB) TX bytes:67598 (66.0 KiB)
09.48.735970243
TX packets:304 errors:0 dropped:0 overruns:0 carrier:0
RX bytes:22426 (21.9 KiB) TX bytes:128316 (125.3 KiB)
09.49.746649199
TX packets:304 errors:0 dropped:0 overruns:0 carrier:0
RX bytes:22426 (21.9 KiB) TX bytes:128316 (125.3 KiB)
09.50.757276807
TX packets:347 errors:0 dropped:0 overruns:0 carrier:0
RX bytes:24012 (23.4 KiB) TX bytes:184214 (179.8 KiB)
09.51.767121736
TX packets:347 errors:0 dropped:0 overruns:0 carrier:0
RX bytes:24012 (23.4 KiB) TX bytes:184214 (179.8 KiB)
09.52.777232744
TX packets:405 errors:0 dropped:0 overruns:0 carrier:0
RX bytes:26352 (25.7 KiB) TX bytes:258700 (252.6 KiB)
09.53.787515822
TX packets:405 errors:0 dropped:0 overruns:0 carrier:0
RX bytes:26352 (25.7 KiB) TX bytes:258700 (252.6 KiB)
09.54.798234461
TX packets:463 errors:0 dropped:0 overruns:0 carrier:0
RX bytes:28288 (27.6 KiB) TX bytes:337288 (329.3 KiB)
09.55.808966342
TX packets:463 errors:0 dropped:0 overruns:0 carrier:0
RX bytes:28288 (27.6 KiB) TX bytes:337288 (329.3 KiB)
09.56.820653126
TX packets:515 errors:0 dropped:0 overruns:0 carrier:0
RX bytes:30476 (29.7 KiB) TX bytes:405452 (395.9 KiB)
09.57.831554207
TX packets:515 errors:0 dropped:0 overruns:0 carrier:0
RX bytes:30476 (29.7 KiB) TX bytes:405452 (395.9 KiB)
09.58.843085966
TX packets:552 errors:0 dropped:0 overruns:0 carrier:0
RX bytes:32074 (31.3 KiB) TX bytes:448022 (437.5 KiB)
Christopher Hunt
Phil Bedard wrote:
If the normal burst value is too low you may always be exceeding the
normal burst limit. You can do a show int rate-limit to look at
current burst values.
Phil
On Jun 19, 2008, at 12:00 PM, Christopher Hunt wrote:
Sorry,
The rate-limit statement that results in 0.2mbps throughput is:
rate-limit input 10000000 5000 5000 conform-action transmit
exceed-action drop
-------- Original Message --------
Subject: TCP behavior under strict CAR rate-limiting
Date: Thu, 19 Jun 2008 08:11:36 -0700
From: Christopher Hunt <[EMAIL PROTECTED]>
Organization: ReachONE Internet Inc.
To: cisco-nsp@puck.nether.net
Please excuse me if this is off-topic. I'm needing some expert TCP
analysis and not sure where to turn. I'm experimenting with CAR
rate-limiting using the Cisco IOS. I am using Iperf to test TCP
throughput, PRTG to poll the Cisco interface traffic levels each
second and Wireshark to capture the packets. This is a lab, so there
are no public IPs in use. Using the rate-limit statement
"rate-limit input 10000000 1875000 3750000 conform-action transmit
exceed-action drop" I see expected behavior, that is an average of
10mbps with bursts up to ~18mbps.
Using the rate-limit statement "rate-limit input 10000000 1875000
3750000 conform-action transmit exceed-action drop" I see an average
of 0.02mbps (200 bits/second) with no bursting at all.
I expected that the cause would be excessive drops by the Cisco
interface causing the TCPs on either end to negotiate a low
tcp_receive_window, but the packets don't bear that out. The window
sizes are staying high. The cisco interface doesn't show many drops
nor does it ever seem to receive the 10mbps rate, even for a second.
I expect that even retransmits, duplicate ACKS etc. would increment
packet counters on the Cisco.Any ideas what else could cause low
throughput besides a low tcp_receive_window?
--
Christopher Hunt
--
Christopher Hunt
ReachONE Internet, Inc.
(888)820-7559
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