The strangest cable modem issue

Drumm, Dan ddrumm at ball.com
Mon Aug 23 16:09:43 UTC 2004


I thought I'd ask NANOG this, since somebody may be from a large cable
operator and may know. I am a Comcast customer and don't want to call
this in through tech support, as I've tried that before without any
success.

 

I use my cable modem normally - to surf the web, to play a game or two,
and to listen to stream casts. I have a buddy who often needs tech
support, so I use RAdmin (http://www.famatech.com/radmin/) to login to
his computer and go through stuff with him. I use large TCP packets,
small UDP packets - ICMP, ESP - large and small.

 

RAdmin can transfer files from desktop to desktop. Ethereal reveals this
is a standard TCP based protocol used on the RAdmin port tcp/4899. If I
want him to have a file, I push it that way. 

 

Last night - I decided to start IIS FTP server, and have him use his
SmartFTP (www.smartftp.com <http://www.smartftp.com/> ) client to pull
several larger files from me. I poked a hole in the Linksys router's
port forwarding for FTP and off we went. He grabs the first file, and
it's going along at roughly the correct uplink speed for Cable (20 KB/s
or so) and all is fine. Then, my cable modem reboots. Stops dead. All
the lights go off and start blinking, a full reload. It grabs the same
IP address via DHCP and he restarts. Again, about 15 seconds into the
download, it crashes the cable modem. We do this about 5 times to really
make sure it's just FTP doing this.

 

I have a DOCSIS 1.1 modem from RCA
(http://www.rca.com/product/viewdetail/0,2588,PI700502-CI700094,00.html?
)

I have a Linksys BEFSR81
(http://www.linksys.com/products/product.asp?prid=155&grid=5) with the
latest firmware

 

FTP is the only protocol that does this. Using RAdmin file transfer, I
push files to him over tcp/4899 and it doesn't happen.  

 

The cable modem is somewhat old, perhaps it needs to be flashed with a
newer image, but I am not sure what could cause it. 

 

Ideas?

 

 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.nanog.org/pipermail/nanog/attachments/20040823/b881d736/attachment.html>


More information about the NANOG mailing list