Subject: Timeout issues using a wireless modem...

From: "Edward Baichtal" <[email-masked]>
Date: Mon, 30 Nov 1998 12:39:16 -0800

I've got a wireless modem (CDPD) hooked up to a Win98 machine.  When
connecting to my wu-ftp server which is on a Linux box and on the internet
as well, the connection times out and fails.  This is using the DOS FTP
client.  However using IE I connect immediately but when I click on a file
to download, I get a 2-3 minute lag before the file starts downloading.

Microsoft FTP servers come back instantly and work just fine.

Tried ftp.redhat.com, and other UNIX FTP server sites that I know of, and
they also time out over the wireless modem.  When I run the modem under
RedHat 5.2, there's a 3 minute lag before connecting to a UNIX FTP server,
and Microsoft FTP servers connect instantly.

I have also observed that there is a lag that's noticeable when I try FTP
over my DSL connection.  There's a few seconds of lag going to a wu-ftpd
server and then I get the login prompt.

So my question is, is this by design?  Is there a timeout I can fix on the
server end?  Is this because wu-ftpd is more security minded and might drop
a slow response?  I traced packets and observed that packets from the
wireless modem have a half second delay, might this make wu-ftpd drop the
connection thinking it's a flood attack?

FTP Server: Version wu-2.4.2-academ[BETA-17] on RH 5.0, Pentium 120mhz.

--------------------------
Edward Baichtal
[email-masked]
http://www.airlink.com

---

From: Gregory A Lundberg <[email-masked]>
Date: Mon, 30 Nov 1998 16:30:02 -0500 (EST)

On Mon, 30 Nov 1998, Edward Baichtal wrote:

> connecting to my wu-ftp server which is on a Linux box and on the
> internet as well, the connection times out and fails.  This is using
> the DOS FTP client.  However using IE I connect immediately but when I
> click on a file to download, I get a 2-3 minute lag before the file
> starts downloading.

IE's ftp client is primitive.  Probably what you're seeing (whe it's fast
at the beginning) is cached locally.  the long lag tstart the download is
the real connection  and that sounds like the same behavior as the
command-line client.

> Tried ftp.redhat.com, and other UNIX FTP server sites that I know of,
> and they also time out over the wireless modem.  When I run the modem
> under RedHat 5.2, there's a 3 minute lag before connecting to a UNIX
> FTP server, and Microsoft FTP servers connect instantly.

Not surprising, virtually anyone who's anyone running a serious ftp site
runs wu-ftpd.  Frankly, the scary thing is that the ftp server from MS
doesn't have problems.

> I have also observed that there is a lag that's noticeable when I try
> FTP over my DSL connection.  There's a few seconds of lag going to a
> wu-ftpd server and then I get the login prompt.
> 
> So my question is, is this by design?

No.

> Is there a timeout I can fix on the server end?

Yes, by hacking the source.

> Is this because wu-ftpd is more security minded and might drop a slow
> response?

wu-ftpd is *FAR* more security-minded than the stuff MS foists on the
unsuspecting.

> I traced packets and observed that packets from the wireless modem
> have a half second delay, might this make wu-ftpd drop the connection
> thinking it's a flood attack?

What?  You seeing a lot of TCP SYNs fired off before the server machine
can ACK them?  WU-FTPD isn't on the scene at that point.  Linux might
declare it a SYN-flood attack.  Or the inetd super-server may decide it's
had enough and shut down the service.  I don't think this is the case,
though.

> FTP Server: Version wu-2.4.2-academ[BETA-17] on RH 5.0, Pentium

My WAG is that all your problems due to incomplete/improper setup of the
client machine, DNS or something like that.  From what you've said, it's a
problem starting the connection and getting a login prompt.

Most of the times I've seen lag connecting to wu-ftpd it was because the
server (or, more usually the tcpwrappers, tcpd) wanted to AUTH (RFC-931)  
the remote user and the client machine wasn't accepting _or_ refusing the
connection causing the AUTH to have to timeout before proceeding with the
ftp session (this happens a lot with firewalls).  I don't believe the MS
FTP server does AUTH and I'm fairly sure there's no such thing as the
inetd super-server or the tcpwrappers on stock MS operating systems ..
like I said, scary.  Anyway, you could try running without tcpd and if
things are faster, you know you need to fix your AUTH problems or live
without the security features you get from using the tcpwrappers.

Other times, I've seen problems with DNS.  The server (and tcpd if you ask
it to) try to reduce IP spoofing by comparing the client machine's IP
number with the results of an IP->name->IP lookup through DNS.  If the DNS
machines are across a slow link, or the DNS/resolver setup on the wu-ftpd
box is bunged up, this can slow things down quite a bit.

Both the above will cause problems getting connected but won't have much
effect once you're connected.  So, if timeouts occur durring transfers,
I'd look at the MTU, packet fragmentation, TCP window size, timeouts, etc.
A lot of this stuff is configurable to some extent or another either in
the setup of the machine or by changing/hacking the daemon.

There are some *very* old messages in the mailing list archives about slow
links to the nether regions of the Internet and hacking the timeouts and
retries to work arround them.  You might want to wade through the archives
if you're gonna hack the source.

The location of the latest version of wu-ftpd can be found in the 
directory
 
      ftp://ftp.academ.com/pub/wu-ftpd/private/
 
You can't see the directory contents, so read the message informing you
of the actual filename to retrieve. It's there.
 
wu-ftpd Resource Center:  http://www.landfield.com/wu-ftpd/
wu-ftpd FAQ:              http://www.cetis.hvu.nl/~koos/wu-ftpd-faq.html
wu-ftpd list archive:     http://www.landfield.com/wu-ftpd/mail-archive/

-- 

Gregory A Lundberg		Senior Partner, VRnet Company
1441 Elmdale Drive              [email-masked]
Kettering, OH 45409-1615 USA    1-800-809-2195