Bogus networking

[Ross Williams]

> Date: Thu, 19 Dec 2002 19:37:11 -0200
> To: mol-general@lists.maconlinux.org
> From: "Marcelo A. Ferreira Gomes" <suporte@mac.com>
> Subject: Re: Bogus networking
> Reply-To: mol-general@lists.maconlinux.org
>
> At 15:58 -0500 19/12/2002, Ross Williams wrote:
>> Hello,
>> I'm new to this list. I started working with MOL two days ago, and
>> it really is the best thing since sliced bread. I'm having a bit of
>> trouble, however, with networking.
>>
>> From Mac OS 10.2.2 I am able to ping my host and even
>> www.google.com, but I cannot access web pages, SSH, or anything that
>> requires a sustained tcp connection. DNS obviously works fine
>> because I can resolve any host I choose. Curiously, I am able to
>> retrieve the source of www.google.com if I telnet to it on port 80
>> and issue the "GET /" command. It still will not load in the web
>> browser. I believe that eliminates iptables MASQUERADE problems,
>> though.
>
> Yes, that's correct. If you can telnet to port 80, there's no problem
> with your masquerade and firewalling rules. But if you look closely
> to the page source you get from the "GET /" command, you'll probably
> see that some parts of the HTML code are missing.
>
>> I ran tcpdump on the linux side, and I came up with traffic to
>> www.google.com that listed the source ip address as "truncated ip".
>> I don't have those logs at my fingertips because I am writing this
>> mail from OS X. I'd be glad to send them if someone requests.
>
> =46or what you describe, I guess I can diagnose it right away. TCP/IP
> has a parameter called MTU, for maximum transmit unit. This is the
> biggest chunk of information that can be sent over your particular
> physical medium in a single packet. On ethernet media, it is close to
> 1500 bytes, but can vary a little bit above or below it, depending on
> whether you have some other protocol on top of it (such as PPPoE, for
> instance). This value is normally guessed right by the OS, in a
> process called PMTU discovery (for path MTU), so you don't need to
> bother wit it.

> Your problem seems to be that Mac OS is getting a wrong value for
> your particular setup. I am currently in the middle of a big mess
> here at home, so I can't conduct networking experiences right now,
> and thus can't even try to reproduce your problem here. But try
> checking out Apple's support or developers sites to find a way to
> force Mac OS X to use a lower value for the PMTU. That way, you won't
> be getting truncated packets, and browsing will work again.
>
I haven't yet, but I will fiddle with the MTU. I do have a bit of 
another issue on this end, however. After fiddling with MoL and also 
the kernel HFS+ driver <http://sf.net/project/linux-hfsplus/> I ended 
up with disk corruption. It seems to affect only files that MoL touched 
during the session--dock preferences, pref files for the programs that 
I have starting on login, etc. I'm posting this part of the message as 
a separate thread, so any comments about the disk put there. Thanks.
> This is an interim solution, until the cause for the wrong PMTU
> discovery can be diagnosed and eliminated. Perhaps there's a problem
> with the sheep net driver, or Linux's tunnel driver. Exactly how are
> you connecting to the network?
>
I'm using the tun drivers. A curious issue is that the driver always 
comes up as tun5 although all the docs seem to indicate that if I'm 
only running one MoL setup it should come up as tun0. I am running no 
other tunnel devices. ifconfig only indicates tun5 as active.
>> I know that this issue has been brought up on the list for months,
>> now, but I've yet to see a definitive solution. No one has seemed to
>> mail back and say, "Yes, it's working."
>
> In a few days, I hope to be back with everything working here, so if
> you can't find the solution you need until then, I'll be glad to
> help, and we'll probably end up with a step-by-step solution to your
> problems.
>
Great, thanks.
>> I'm running MOL 0.9.67 on Debian Woody with a stock 2.4.18-newpmac
>> kernel on a Dual USB iBook. I am aware that the 0.9.67 seems to be a
>> bogus version number or at least not released on the maconlinux.org
>> site. If someone suggests, I could try 0.9.65.
>
> I don't believe this has to do with your particular version of
> hardware, Linux, or maybe even MoL. It seems to be some conflicting
> aspect between your network drivers and your network setup. Do you
> use cable/DSL/somethingelse with PPPoE?
>
I use AirPort as my primary internet. The base station is connected to 
a cable modem through AT&T Broadband. No PPPoE involved; I have a 
static IP.
>> Thanks,
>> Ross Williams
>> overhacked {at} bigfoot {dot} com
>
> You're welcome. ;-)
>
> -- 
> <suporte [at] mac [dot] com>: n=E3o =E9 ".br", mas =E9 mais BR que os 
> outros=
> =2E
> :-)
>
>
>