Cable Modem Troubleshooting Tips

Networking tweaks

• Remove dial-up tweaks
• Install cable tweaks
• Network configuration tweaks  New 2002 Aug 17, updated Aug 31 

Remove dial-up tweaks

If you have previously installed networking tweaks for dial-up modem performance (you might not know you had installed them if your dial-up ISP installation did it for you), you must remove them in order to use the cable modem service. The timings of cable modems are quite different to those of dial-up modems, and certain dial-up tweaks (such as reduced MTU size) will substantially degrade cable modem performance: a virgin Windows ethernet configuration would perform better on cable modem than one which has had dial-up tweaks installed. In extreme cases, or where you have forgotten how to remove the tweaks, re-installation of Windows (a simple re-install, not a re-format) has cured the problem of performance degradation: boot from the Windows system CD-ROM or associated boot diskette. You will need diskettes or CD-ROMs for any special drivers you also need to re-install.

Actually, although a full re-installation of Windows 9x/ME will remove old unwanted tweaks, there is a slightly faster procedure for the confident Windows user. In the control panel Network, in the Properties panel, remove all network adapters (green icons), exit, and allow Windows to restart. It will re-discover all network adapters, and re-install them with fresh settings. You will need your Windows system CD-ROM, and diskettes or CD-ROMs for any drivers required for your network adapters.

Install cable tweaks

A good site for determining whether any tweaking is necessary or desirable is http://www.dslreports.com/tweaks (take the Tweak test: on the results page, declare your connection be be via Normal), but be aware that this site is mainly aimed at xDSL users, and some advice, such as that concerned with PPPoE, does not apply to cable modem users. The only Windows networking tweak which has significant benefit for cable modem users is to increase the TCP Receive Window (RWIN). The RWIN tweak will be more significant to Windows 9x users than to Windows ME/2000/XP or Mac users, who have better default settings.

A site which has good technical information on tweaking cable modem networking for both Windows and Macs (and also debunks many of the myths) is http://cable-dsl.home.att.net/. See also http://www.speedguide.net/Cable_modems/ (which unfortunately also propagates some of the urban myths), but has a useful collection of pre-packaged downloadable cable tweaks at http://www.speedguide.net/Cable_modems/cable_patches.shtml.

The necessary RWIN size for best performance is discussed in the article on Traceroute. The RWIN tweak might make little difference to web browsing performance, because the ISP's transparent caches are very close to your PC, and so the default RWIN setting will be fine. Windows 2000/XP has an adaptive TCP Receive Window, and does not need tweaking.

The optimal MTU size for cable connections is 1500 bytes, leading to an optimal MSS size of 1460 bytes. If the tweak test shows a smaller MTU/MSS, then this might indicate a dial-up tweak that needs to be removed. Smaller than optimal MTU/MSS sizes will significantly damage cable performance.

If your system is Windows 95, 98, or 98SE, you might benefit from the fix downloadable from: http://support.microsoft.com/support/kb/articles/Q236/9/26.asp. This fix is not for any other version of Windows.

Apple Mac users can tweak their network settings with the shareware IPNetTuner, which comes with a pre-defined cable modem tweak configuration. The tweaks last for the current session only: the system reverts to defaults when it restarts or when the TCP/IP stack is deactivated and reactivated, such as on a location switch or re-boot.

I recommend that you make tweaking the last thing you do, after you have corrected any other faults. Get your system working properly first with a standard configuration, before you try the tweaks.

See also the article on Getting Faster Web Browsing for web browser tweaks.

Network configuration tweaks

This section applies primarily if your PC is connected directly to the cable modem: these recommendations are much less important, and maybe even undesirable, if your PC is part of a LAN connected to a NAT router.

Ethernet interface duplex setting

See article Ethernet card: duplex setting.

Disable or uninstall unnecessary network components

Default PC configurations often include network clients, services, and protocols which are of no use on a direct cable network connection. Many of them can generate network traffic, such as search probes, putting needless traffic on the upstream, which can cause latency problems for other more important traffic from your PC. Remember: these changes should only be made if the PC is directly connected to the cable modem: an intervening NAT router will stop this needless traffic anyway.

Windows 2000/XP:

• Open control panel Network Connections.
• Identify the icon for the network interface connecting to the cable modem, right-click it, and select Properties.
• The central scrollable box lists all installed network components. The check-box to the left of the component name will be checked if this component is active on this network interface. A component can be disabled on this interface only by unchecking the check-box. Alternatively, a component can be globally uninstalled from every network and dial-up interface in the PC by clicking its name to select it, and then clicking Uninstall.
• The following components might be worth disabling:
• File and Printer Sharing for Microsoft Networks: this is both a security risk and a source of unnecessary network traffic. It should be disabled unless you are an expert and know what you are doing.
• Client for Microsoft Networks: should be disabled unless you wish to mount drives from a remote PC on the Internet using Microsoft file sharing.
• Client Service for NetWare: should be disabled.
• Service Advertising Protocol: should be disabled.
• SAP Agent: should be disabled.
• NetBEUI Protocol: should be disabled.
• NWLink NetBIOS: should be disabled.
• NWLink IPX/SPX/NetBIOS Compatible Transport Protocol: should be disabled.
• iVLAN Protocol: should be disabled.
• AppleTalk Protocol: should be disabled.
• DLC Protocol: should be disabled.
• The following components, if present, should not be disabled:
• QoS Packet Scheduler: this is harmless and should be left enabled.
• Network Monitor Driver: this is used by the Performance Monitor, is harmless, and should be left enabled.
• Internet Protocol (TCP/IP): this is essential and must be enabled.
• Optimise the remaining network configuration by clicking the name Internet Protocol (TCP/IP) (not its check box) and then click Properties:
• Click the button Advanced...:
• Click tab DNS:
• Uncheck Register this connection's addresses in DNS.
• Click tab WINS:
• Select Disable NetBIOS over TCP/IP, unless either:
• Client for Microsoft Networks is enabled and you wish to mount drives from remote Windows 9x/ME systems; or
• File and Printer Sharing for Microsoft Networks is enabled and you wish remote Windows 9x/ME users to mount your shared resources.
• Disabling NetBIOS over TCP/IP is also a worthwhile security improvement.
• Click OK to close Advanced TCP/IP Settings.
• Click OK to close Internet Protocol (TCP/IP) Properties.
• Click OK to close the Connection Properties.
• [XP only] Disable SSDP Discovery Service: Right-click My Computer and select Manage:
• In the left-hand box, expand Services and Applications, then select Services.
• In the right-hand box, scroll down to find SSDP Discovery Service, and double-click it.
• Set Startup type to Disabled.
• Click Stop.
• Click OK to close SSDP Discovery Service Properties.
• Close Computer Management.

Win 95/98/ME:

• Open control panel Network.
• The central scrollable box lists all installed network components. From amongst the components with green adapter icons, identify the network interface that connects to the cable modem. We shall refer to the name of that interface as [cable interface] below.
• With a single-click, select the component with the green adapter icon entitled [cable interface].
• Click the button Properties...
• Click tab Bindings:
• Uncheck every protocol listed except these (if present):
• TCP/IP -> [cable interface]
• Internet Connection Sharing (protocol) -> [cable interface]
• Click OK to close [cable interface] Properties.
• With a single click, select the protocol component with the plug-and-wires icon entitled TCP/IP -> [cable interface].
• Click the button Properties...
• Click tab Bindings.
• The following clients and services might be worth disabling by unchecking the check box beside their name:
• File and printer sharing for Microsoft Networks: this is both a security risk and a source of unnecessary network traffic. It should be disabled unless you are an expert and know what you are doing.
• Client for Microsoft Networks: should be disabled unless you wish to mount drives from a remote PC on the Internet using Microsoft file sharing.
• all other clients or services listed in the bindings should be disabled.
• Click OK to close TCP/IP Properties.
• If you have only one network card, then instead of unbinding the clients and services from one instance of the TCP/IP protocol as above, you may instead select with a single click the component with the blue icon entitled File and printer sharing for Microsoft Networks and click Remove, and again for Client for Microsoft Networks. However, removing the Client might leave you with problems in saving passwords for various features.
• Click OK to close the Network control panel, and allow Windows to restart.

Apple Mac OS 8.x/9.x: if the ethernet port is connected directly to the cable modem, disable AppleTalk protocol on the ethernet port as follows:

• Open control panel AppleTalk:
• EITHER:
• set the pull-down Connect via: to some port other than the one connected to the cable modem;
• OR:
• If an Options button is not visible, pull down the Edit menu, select User Mode, and select Advanced, click OK.
• Click the button Options....
• Select Inactive
• Click OK
• Close the control panel.

Apple Mac OS X: if the ethernet port is connected directly to the cable modem, disable AppleTalk protocol on the ethernet port as follows:

• Pull down the Apple menu and select System Preferences...
• Click Network.
• In the pull-down Show: select the interface in use;
• Click tab AppleTalk;
• Uncheck Make AppleTalk Active;
• Close System Preferences.

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