Web server problems outside LAN with pages above about 1.1 KB(browsers hang)

I have a web server on my home network. It works fine with requests
coming from the LAN, but browsers hang when connecting from the outside.

Now, my first thought was a problem in the firewall setup. But the
catch is, the web server _is_ accessible, since accesses by outside
browsers are logged by the web server. Inspecting the logs, nothing
seems to be a problem, since accesses from the outside are logged as 200
(OK). And a server configuration problem is also unlikely -- I've tried
with both Apache and thttpd with various configuration and trying
different ports, same problems.

I think the key is that I cannot serve pages above a certain (very
small) size, about 1.1 KB. Browsers just hang, saying "waiting for
[server]...". Smaller pages are no problem.

I've run out of ideas about how to fix this. Help and pointers will be
greatly appreciated.

--
Henrik S. Hansen

Henrik S. Hansen wrote:
> I have a web server on my home network. It works fine with requests
> coming from the LAN, but browsers hang when connecting from the outside.
>
> Now, my first thought was a problem in the firewall setup. But the
> catch is, the web server _is_ accessible, since accesses by outside
> browsers are logged by the web server. Inspecting the logs, nothing
> seems to be a problem, since accesses from the outside are logged as 200
> (OK). And a server configuration problem is also unlikely -- I've tried
> with both Apache and thttpd with various configuration and trying
> different ports, same problems.
>
> I think the key is that I cannot serve pages above a certain (very
> small) size, about 1.1 KB. Browsers just hang, saying "waiting for
> [server]...". Smaller pages are no problem.
>
> I've run out of ideas about how to fix this. Help and pointers will be
> greatly appreciated.
>

Could be an MTU problem when the response is sent to the internet.
Try to set MTU of eth0 (or whatever, using ifconfig) to asmaller
size == 1400 (instead of 1500) and repeat the test.

I had such a problem with ssh and scp.

ssh worked well, but uploading files (with scp) larger than 1300
Bytes failed. I decrease MTU to 1300 and it worked.
Was a problem with FreeSWAN and IPsec-tools in Kernel 2.6.x.

Toni

Toni Erdmann <for-spammers-(E-Mail Removed)> writes:

>> I think the key is that I cannot serve pages above a certain (very
>> small) size, about 1.1 KB. Browsers just hang, saying "waiting for
>> [server]...". Smaller pages are no problem.
>> I've run out of ideas about how to fix this. Help and pointers will
>> be
>> greatly appreciated.
>
> Could be an MTU problem when the response is sent to the internet.
> Try to set MTU of eth0 (or whatever, using ifconfig) to asmaller
> size == 1400 (instead of 1500) and repeat the test.

That's it! I changed the MTU of eth1 to 1000, and the problem's gone.
Thanks a lot, Toni! You saved my day. I guess I looked all the wrong
places.

--
Henrik S. Hansen

Henrik S. Hansen wrote:
> Toni Erdmann <for-spammers-(E-Mail Removed)> writes:
>
>
>>>I think the key is that I cannot serve pages above a certain (very
>>>small) size, about 1.1 KB. Browsers just hang, saying "waiting for
>>>[server]...". Smaller pages are no problem.
>>>I've run out of ideas about how to fix this. Help and pointers will
>>>be
>>>greatly appreciated.
>>
>>Could be an MTU problem when the response is sent to the internet.
>>Try to set MTU of eth0 (or whatever, using ifconfig) to asmaller
>>size == 1400 (instead of 1500) and repeat the test.
>
>
> That's it! I changed the MTU of eth1 to 1000, and the problem's gone.
> Thanks a lot, Toni! You saved my day. I guess I looked all the wrong
> places.
>

There's a thread about this ongoing in a german news group here.
The hint is to check the firewall too. Normally, if your server
sends IP packets that are too long, the router (of the ISP) will
send an appropriate ICMP message telling him about this. Your
server can react and reduce the MTU.

But if your firewall blocks incomming ICMP message, your server
can't receive them and therefore can't react correctly.

That's when/why you have to do it manually.

Toni

Doug Laidlaw wrote:

> Henrik S. Hansen wrote:
>
>> Toni Erdmann <for-spammers-(E-Mail Removed)> writes:
>>
>>>> I think the key is that I cannot serve pages above a certain (very
>>>> small) size, about 1.1 KB. Browsers just hang, saying "waiting for
>>>> [server]...". Smaller pages are no problem.
>>>> I've run out of ideas about how to fix this. Help and pointers will
>>>> be
>>>> greatly appreciated.
>>>
>>> Could be an MTU problem when the response is sent to the internet.
>>> Try to set MTU of eth0 (or whatever, using ifconfig) to asmaller
>>> size == 1400 (instead of 1500) and repeat the test.
>>
>> That's it! I changed the MTU of eth1 to 1000, and the problem's gone.
>> Thanks a lot, Toni! You saved my day. I guess I looked all the wrong
>> places.
>>
> Don't we all! My first thought was a dynamic IP address, but since the
> others can get small pages, that isn't the problem.
>
> Doug.
Just found a note about the MTU issue in the manual for my modem. It
mentions similar problems: emails with large attachments, or Windows Update
won't work. Recommended value for my modem is 1492, but they say to ask
your ISP.

Doug.
--
ICQ Number 178748389. Registered Linux User No. 277548.
Success usually comes to those who are too busy to be looking for it.
- Henry David Thoreau.