recommend me some diagnostic tools

[melts]

hi all
I've got an ADSL connection, set up in bridged mode to a gentoo box that does a whole host of things. I'm seeing poor performance on the link and would like to diagnose the issue, but I'm not sure what tools would be best, since I'm not sure where the problem lies.

Up front I'll say it now, the one thing I haven't tested that I'm dying to test actually, is the modem's performance away from the gentoo box. The site is remote though, and I can't take it offline short of after hours too. I plan on plugging the bridged modem into my laptop and opening a connection with that and doing some testing, however as we only recently replaced the DSL modem hardware and the line seems to get good sync I'm vaguely pessimistic it'll be that.

ok, so the guts of the issue is; the modem stats page show it as syncing at 22,000/1,000 Down/Up kbits/sec and with a good SNR. However, hitting a site from the LAN clients this box MASQ's for is rather slow, with delays before data starts to come down, bursts of data followed by long slow tails (ie files downloading the first few hundred kbytes at around 200kbyte/sec then dropping to ~90kbyte/sec, and it will get worse)

On the linux box itself, wget shows the same peaky then slow downloads, hitting the ISP FTP site (using ISP's adsl.test files on their FTP) the further away the hosts the slower the downloads go, too. This lead me to believe the MTU was all wrong, but I've set it with ifconfig for the ppp interface, and used the iptables --clamp-mss-to-pmtu setting for the interface to no avail.

Also what annoys me if I never see anything more than around 200kbytes/sec when the link top speed should be approaching 2mbytes/sec. Using slurm -i ppp0 the max speed has never been above 350kbytes/sec.

I can post all the iptables/dmesg/ifconfig/logs and so on if required, but I'd most of all like to know what tools and commands I can use to look at the issue and start to understand the problem better. I'm willing to believe its anything, from system hardware to ISP throttling gone crazy, but I need to be able to pinpoint it accurately before I start planning out of hours adventures
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doh
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[gerdesj]

Tools:

ping - it does a lot more than you think!
nettop - console based
ntop - web frontend, huge amount of stats
wireshark - look at the packets themselves
smokeping

... and lots of others

Can we have some more details, its possible that someone will have some advice:

Your ADSL connection - PPPoA or E or something else - eg in the US I think PPPoE is standard but in the UK and probably much of Europe PPPoA is the norm?
What model of modem?
What country are you in?
What ISP?
What is the SNR and also what is the Attenuation (Loop ATT or similar) if applicable.
On you Linux box - what kernel version

I have a ~20Mbit s-1 connection and I can get >1600KByte s-1 on a download. Now 1600 x 8 (8 bits to the byte) = 12,800 and allowing for ATM frames, IP and TCP overhead that seems pretty fair to me.

That would seem to be a good target to aim for.

As you say, you need to get some perspective on the problem. I would not recommend getting too deep into fancy diag tools until you have tried a few different systems driving the connection.

Give us some answers to the above questions and I'm sure we can get to the bottom of this.

Cheers
Jon

[melts]

tp be honest I've been trying a bit, and the box already runs ntop for tracking issues, its just been so slippery

the questions i can answer;
ADSL connection is PPPoE, its been set up starting with net.ppp0 but the config for it isnt in /etc/conf.d/net and also it doesn't seem to listen to the settings in /etc/ppp/pppoe-options - this bit confuses me but its hard to sort out why its doing it. it gets the static IP via DHCP, uses the secrets in chap-secrets and doesn't listen to the MTU setting in the options file...

Modem is a Linksys WAG120N

I'm in Australia and the client's ISP is westnet/iiNet, they are on an iiNet business plan for this account, and generally iiWestNet don't do stupid things with contention ratios and the like, a friends on the same exchange and is getting the expected throughput.

For some reason the modem won't give up the SNR and ATT. I found the URL for the hidden page for it on the modem, but the figures are missing, it has the measured units but not the value, disappointing. some info;
Vendor: Linksys
ModelName: WAG120N
Firmware Version: A1.00.12 , 2010-01-26T06:39:37

The linux box is running a current kernel, uname -a
Linux ns 2.6.36-gentoo-r5-melts #3 SMP Sat Mar 12 06:27:25 WST 2011 x86_64 AMD Athlon(tm) 64 X2 Dual Core Processor 4600+ AuthenticAMD GNU/Linux

when I do get the chance I'll be hooking up my laptop and testing the hardware. I might even use one of my spare open modems as the firmware on them seem to be more helpful monitoring wise.

I just don't know what I'll do if the modem works fine on my laptop and still has this frustrating performance through the linux box

Thanks for the interest
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doh
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