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From: Alvaro Saurin <saurin@dcs.gla.ac.uk>
Date: Mon, 5 Dec 2005 12:51:56 +0000
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FILETIME=[D118E7B0:01C5F999]
Subject: Dummynet and fragments
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Hi,
I was wondering if someone could help me with a small problem with
dummynet. I have a typical dumbbell configuration where I have a
FreeBSD 6.0 machine with dummynet. It is something like this:
*----- ubuntu6
| 10.10.3.6
10.10.1.3 10.10.1.4 |
ubuntu2 ---[hub]--- ubuntu3------- BSD4------[hub]--- ubuntu5
10.10.2.2 | 10.10.2.3 10.10.3.4 10.10.3.5
|
ubuntu1 -----*
10.10.2.1
I want to set the delay, bandwidth, etc. limit in BSD4, using
something like
> sudo ipfw add 3 pipe 3 all from ubuntu2 to ubuntu6
> sudo ipfw add 4 pipe 4 all from ubuntu6 to ubuntu2
> sudo ipfw pipe 3 config bw 12000Kbit/s queue 17500bytes
delay 5ms
> sudo ipfw pipe 4 config bw 12000Kbit/s queue 17500bytes
delay 5ms
for a limit between 'ubuntu2' and 'ubuntu6', leading to a new rule
set like
> sudo ipfw -a list
00003 0 0 pipe 3 ip from 10.10.2.2 to 10.10.3.6
00004 0 0 pipe 4 ip from 10.10.3.6 to 10.10.2.2
00100 1862 144376 allow ip from any to any via lo0
00200 0 0 deny ip from any to 127.0.0.0/8
00300 0 0 deny ip from 127.0.0.0/8 to any
65000 118952 53165334 allow ip from any to any
65100 0 0 deny log logamount 5000 ip from any to any frag
65535 8 512 deny ip from any to any
> sudo ipfw pipe show
00003: 12.000 Mbit/s 5 ms 17 KB 0 queues (1 buckets) droptail
00004: 12.000 Mbit/s 5 ms 17 KB 0 queues (1 buckets) droptail
The problem comes here: if I 'ping' between these two machines,
everything is fine, but if I 'ping' with a packet size of, ie, 2000,
no packets arrive at the receiver. Does it have to do with fragmented
packets? Do I have to include any other rule for dealing with fragments?
And another question: why do I need to specify a 5ms delay for a
total RTT of 40ms?
Thanks in advance
Alvaro
--
Alvaro Saurin <alvaro.saurin@gmail.com> <saurin@dcs.gla.ac.uk>