Cable Modem Troubleshooting Tips

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NTL/BY Tech Support.

Peer-to-Peer file sharing issues

If you run a Peer-to-Peer (P2P) file sharing system such as KaZaA, Morpheus, Grokster, Gnutella, LimeWire, WinMX, or eDonkey2000, you may expect the following problems unless you make specific configuration changes:

your cable modem connection will be continually hitting the rate cap, leading to apparent poor bandwidth for other applications;
your ping times will look bad;
your traceroutes will look bad, even on the very first hop to the local UBR;
your online games will show terrible latency;
your firewall might detect hundreds or thousands of incoming connection attempts;
if your PC is behind a NAT router, the P2P application might not work properly.

Be aware that most P2P systems will run in the background even when their window is not open. Because of their P2P nature, they are capable of loading your cable connection even when you are not downloading files: other users might be causing your PC to be uploading to them, or your PC might be acting as a SuperNode server, passing on search requests from other P2P clients.

The problem of hitting the rate cap is the same in nature as that described for on-line gaming. The P2P application sees a network connection via an ethernet or USB interface and assumes a fast network such as a LAN. It does not realise that the cable modem connection will impose a rate cap. As soon as P2P traffic hits the rate cap (especially the upload rate cap), ping times will go through the roof, and other applications will suffer. The general strategy to avoid this is:

if the P2P application supports its own internal rate capping, configure the internal rate cap to be substantially less than the cable modem upload rate cap;
if it doesn't, make sure that you can totally close down the P2P application when using other critical applications, such as online games;
on a low bandwidth cable connection (e.g. 32 kbps upload cap or less), you must turn off SuperNode support.

The P2P application will expect to receive incoming connections from other users. If you run a firewall or a NAT router, you must configure them to accept those connections, otherwise the P2P application might not work properly, and/or your firewall log might be inundated with messages about attempted connections.

KaZaA, Grokster configuration

KaZaA, Grokster, and similar systems are based on the FastTrack P2P file sharing system, and share a common network. The old Morpheus used to use this network, but now uses Gnutella (see below).

For the FastTrack P2P file-sharing system system to work correctly, you must arrange for incoming connections on port 1214 to be accepted. With a NAT router, you must port-forward port 1214 to the local PC that is running the FastTrack P2P application. With a firewall, you must configure the firewall to permit incoming connections from anywhere in the world to the local port 1214, or grant Server rights to the P2P application.

To configure (based on the KaZaA, the others should be similar):

Pull down the Tools menu and select Options...
Click tab Traffic to bring it to the front, then:

if you do not wish other users to download files from you, check the box Disable sharing of files with other KaZaA members;
otherwise, in the box You can define the maximum number of simultaneous uploads here, set a very low number. For a cable modem upload cap of 64 kbps or worse, this number should be 1. For an upload cap of 128 kbps, set 1 or 2 at most.

Click tab Advanced to bring it to the front, then:

In the select-box Maximum bandwidth in kilobits to be used for transferring files to other KaZaA members, select a value which is the highest below, but not equal to, your cable modem upload cap in kilobits per sec. For instance:

on the NTL 600kbps service (128kbps upload) select 64;
on the NTL 128kbps service (64kbps upload) select 32;
on the Blueyonder 512kbps service (128kbps upload) select 64.

If you do not wish to function as a SuperNode, then check the box Do not function as a SuperNode. The FastTrack P2P file sharing network would collapse if every user checked this box, as it relies on the P2P community of users contributing their PCs as distributed servers, but here are some legitimate reasons for opting out of being a SuperNode:

Your cable modem upload cap is 64 kbps or less;
The PC is behind a NAT router and you have not been able to forward incoming traffic on port 1214 to this local PC;
The PC is behind a firewall and you have not been able to open port 1214 for incoming connections from arbitrary callers through the firewall.

Click OK to close the Options dialogue.

To close down KaZaA completely, right-click its icon in the system tray, and select Close KaZaA, rather than the default Hide KaZaA.

Gnutella, Morpheus, LimeWire, BearShare configuration

The Gnutella P2P file sharing protocol is used by BearShare, Gnotella, Gnucleus, LimeWire, Phex, SwapNut and similar applications, and the new Morpheus has changed to using this protocol.

For the Gnutella P2P file-sharing system system to work correctly, you must arrange for incoming connections on port 6346 to be accepted. With a NAT router, you must port-forward port 6346 to the local PC that is running the Gnutella P2P application. With a firewall, you must configure the firewall to permit incoming connections from anywhere in the world to the local port 6346, or grant Server rights to the P2P application.

To configure Morpheus Preview Edition:

Pull down the Edit menu and select Preferences... (or click Preferences button).
Click on Bandwidth. Check Limit upload bandwidth to and enter a figure in kiloBytes/sec which represents about three-quarters of your cable modem upload rate cap. For instance:

on the NTL 600kbps service (128kbps upload) you would set about 12
on the NTL 128kbps service (64kbps upload) you would set about 6
on the Blueyonder 512kbps service (128kbps upload) you would set about 12

If either (a) the MorpheusPE PC is behind a firewall and port 6346 has not been opened through to this PC, or (b) the MorpheusPE PC is behind a NAT router and port 6346 has not been forwarded to this PC, then click Firewall and check I am behind a firewall. Otherwise, if it possible for outside callers to connect to port 6346 on this PC, uncheck this box.
If the MorpheusPE PC is behind a NAT router, then click Local and check the box Set local IP to, and in the box enter the public WAN address of your cable connection (see What's my IP address? and remember that this can change from time to time). If the MorpheusPE PC is connected directly to the cable modem, uncheck this box.
Click OK to close the Local Properties panel.

To configure LimeWire:

Pull down the Tools menu and select Options.
Click on Speed. In the drop-down, select Cable/DSL if your upload rate cap is 128 kbps or higher, or Modem if it is less than 128 kbps.
Click on Uploads. Adjust the slider Upload Bandwidth so that the figure shown after Upload Speed KB/s is roughly three-quarters of your cable modem upload cap, as expressed in kiloBytes/sec. For instance:

on the NTL 600kbps service (128kbps upload) you would set about 12;
on the NTL 128kbps service (64kbps upload) you would set about 6;
on the Blueyonder 512 kbps service (128kbps upload) you would set about 12.

If the LimeWire PC is behind a NAT router, and if you have successfully configured the router to port-forward incoming connections for port 6346 to this PC, then turn down the arrow beside Advanced and click Firewalls. Check Force IP, and in the box Address enter the public WAN address of your cable connection (see What's my IP address? and remember that this can change from time to time).
Click OK to close the Options panel.

To close down LimeWire completely, right-click its icon in the system tray, and select Exit.

To configure BearShare:

Pull down the Setup menu and select Connection.
In the box Network Interface, check Other, and in the box enter the rate in kilobits per second of your cable modem upload cap. For instance:

on the NTL 600kbps service (128kbps upload) you would enter 128,
on the NTL 128kbps service (64kbps upload) you would enter 64;
on the Blueyonder 512kbps service (128kbps upload) you would enter 128.

In the box Firewall Settings:

If either (a) the BearShare PC is behind a firewall and port 6346 has not been opened through to this PC, or (b) the BearShare PC is behind a NAT router and port 6346 has not been forwarded to this PC, then check the box This computer cannot accept incoming TCP/IP connections. Otherwise, if it possible for outside callers to connect to port 6346 on this PC, uncheck this box.
If the BearShare PC is behind a NAT router, then check the box Report the IP address for accepting connections, and in the box enter the public WAN address of your cable connection (see What's my IP address? and remember that this can change from time to time). If the BearShare PC is connected directly to the cable modem, uncheck this box.

In the box Recommended Settings, click the button Reset... to tune BearShare to the settings you have just entered. This will change various settings in other panels.
Click OK to close the Setup panel.

To close down BearShare completely, pull down the File menu and select Exit, or right-click on its icon in the system tray, and select Exit.

WinMX configuration

For the WinMX P2P file-sharing system system to work at its best, you must arrange for incoming TCP connections on port 6699, and incoming UDP connections on port 6257, to be accepted. With a NAT router, you must port-forward TCP port 6699 and UDP port 6257 to the local PC that is running the WinMX P2P application. With a firewall, you must configure the firewall to permit incoming connections from anywhere in the world to the local TCP port 6699 and UDP port 6257, or grant Server rights to WinMX. If you are unable to open these ports, you can configure WinMX to cope with that.

To configure WinMX:

Pull down the Settings menu and select Connection.
In the pull-down box Connection Speed, select the speed which is next below your cable modem upload rate cap. For instance:

on the NTL 600kbps service (128kbps upload) you would select 64K ISDN
on the NTL 128kbps service (64kbps upload) you would select 56K Modem
on the Blueyonder service (128kbps upload) you would select 64K ISDN.

Click button Filewall/Network Settings.

If you had been able to open TCP port 6699 through any firewall or NAT routers (or if you have no firewalls or NAT routers), then check Listen on port 6699.
If you had not been able to open TCP port 6699, then check Unable to accept incoming connections.
Click OK to close Network Settings.

Click OK to close Connection Settings.

eDonkey2000 configuration

For the eDonkey2000 P2P file-sharing system system to work, you must arrange for incoming TCP connections on port 4662, and incoming UDP connections on port 4665, to be accepted. With a NAT router, you must port-forward TCP port 4662 and UDP port 4665 to the local PC that is running the eDonkey2000 P2P application. With a firewall, you must configure the firewall to permit incoming connections from anywhere in the world to the local TCP port 4662 and UDP port 4665, or grant Server rights to eDonkey.

To configure eDonkey2000:

Click Options.
In the box Max Upload Speed enter a figure which is roughly half of your cable modem upload cap, as expressed in kiloBytes/sec. For instance:

on the NTL 600kbps service (128kbps upload) you would enter about 8
on the NTL 128kbps service (64kbps upload) you would enter about 4
on the Blueyonder 512kbps service (128kbps upload) you would enter about 8.

Click OK to close Options.

A helper application, the eDonkeyBot, is available from http://www.file-finder.com/. It features some automatic bandwidth regulation.