Cannot download using my cable modem

  • Thread starter Thread starter Peter
  • Start date Start date
P

Peter

I just had a cable modem installed. I can make the
connection to internet fine. The problem I have is that I
cannot download files using Save Target As. The dialog
comes up, but no data downloads. This is the same for both
IE (5.5) and NS (6.2). In addition I see that every now
and then, not all show up when accessing web pages. It
doesn't matter that I wait.

To confuse the matter, when I use the same computer but
instead of using the cable modem, I use the dialup
connection I do not see these problems. I can do downloads
and images show up.

I tried another computer with the cable connection, and
that computer works fine. Thus, there is something on this
computer that works differently for cable connection then
dialup.

Does anyone have any hints or suggestions? Anything is
welcome.
 
This very much sounds like an "MTU" issue.

MTU stands for "Maximum Transmission Unit".
It is an internal TCP/IP setting that controls how much
data can be stuffed in to each IP frame that gets
sent to the other end.

The default MTU size is different for each type of
network. It is 1500 bytes for the Ethernet adapter
you are probably using.

In most cases TCP/IP, the equipment and the applications
will properly negotiate a correct MTU, but sometimes
this doesn't happen and you get the kind of symptom
you are seeing. For example, if you have firewall
software that blocks the "ICMP" information that
helps negotiate the MTU size you can encounter this.

For rather arcane reasons "PPPoE" networks -- such as
newer cable and DSL connections -- have smaller
MTUs in the range of 1400 to 1492, leading to
this problem. You actually can test this yourself
using a simple "ping" command. Pick any public IP
address you like and then use this command to 'ping' it:

ping <address> -f -l 1472

This will ping out 1472-byte data packets that aren't
permitted to be broken up in to smaller chunks.
(There is an additional 28-byte TCP/IP overhead to
add to the data size, which gets you to the magic 1500.)
If this gives you a 'packet can't be fragmented' error, MTU
issues may well be your problem. Keep adjusting
the 1492 downward until the error goes away, add 28
to that number, and that is your MTU.

If you have a router between your computer and
the cable modem, it may be configurable to adjust the
WAN MTU size. Otherwise if the cable company gave
you software, it should handle this. As a last resort
you can adjust the TCP/IP MTU size for your machine's
network adapter in the Win2K registry. There is an article
in the MS KB that explains how to do this, and it is also
widely documented on the Internet.

But before you start twiddling registry parameters, I'd
really suggest that you contact your cable company support
to find out if they have a recommended solution, and
to verify that is your problem. If they don't know what
you're talking about (which is quite possible), you haven't really
lost anything.

Steve Duff, MCSE
Ergodic Systems, Inc.
 
Sorry, out of ideas for you on this. You might try reposting
here on in the IE forum.

Steve Duff, MCSE
Ergodic Systems, Inc.
 
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