ISDN Trouble-shooting

1. DETERMINE WHAT THE PROBLEM IS: More than likely you already know that you have no Internet access. The first step is to figure out where the connection is dying out. The best process for doing so is by “process of elimination.” First, if you have no access to email or web sites, power cycle the unit. This means; turn the router off, leave it off for roughly 20 seconds; unplug the ISDN line from the back of it; plug the ISDN line back in; turn the router back on. When the router is turned back on it will reset the ISDN line and restore the system memory resources. When the test light stops flashing, you should have a power light, D light (symbolizes signal from ISDN line), and a link light. When you see this, open the browser and attempt to find a web page.

2. NO D-CHANNEL LIGHT: If the D light on the router does not come on after the test, it means that no signal was picked up. If this happens, turn off the router for at least a minute and turn it back on. If the D light stills sits unlit, unplug the ISDN line from the router and dial the SPIDS. The SPIDS are the actual phone numbers that identify the ISDN circuit with your phone line provider. If the ISDN line is configured for Voice and Data, the phone should ring through. If the Data/Voice ISDN lines respond busy, then there is a problem with the line. If you simply have “data only” ISDN lines, you will get a normal busy signal. If you get an operator message with either line type or the D-Channel light is off you should call your phone carrier and open a trouble ticket.

3. D-CHANNEL LIGHTS UP: With the D light on, try accessing the web. The router should dial up and then the web page should be available. If no site comes up, check to see if B1 and B2 lights are on. B1 and B2 show that the ISDN line is in use represents both channels for the ISDN line. If the lights are on but you are still unable to transfer date try pinging our DNS (64.7.161.12). If no reply, try a trace route to our DNS server and find where the connection fails.

Pinging the router: Make sure that workstation can ping the router on the network. To ping the router on the network, first you will need to find the IP address of the router. You can do this by clicking Start --> Run --> [type] Command [hit Enter]. At the DOS prompt [type] winipcfg (for win9x) or [type] ipconfig (for winNT, Win2k, winME, winXP). Find the “Gateway Address” from the information that appears and try and run the ping command below. To do this, click Start --> Run --> [type] Command [hit Enter].

From there, [type]: ping [IP Address/domain of the destination you are trying to reach]. (Example: ping 192.168.0.1). If the user is unable to ping the router there may be a dead cable or hub. There also might be a server that needs to be rebooted. If you have a more complex LAN (Local Area Network) setup, there is another useful command that helps to pinpoint exactly where the connection is dying. It is called ‘Trace Route’ and is similar to a ping in how it transmits a packet to a destination address. But, a Trace Route illustrates every jump that the data packet takes before reaching the destination address. This command can be executed by clicking Start --> Run --> [type] Command [hit Enter]. Once at the command prompt [type] tracert [IP Address/domain of destination you are trying to contact]. (Example: tracert 192.168.0.1). Use a destination IP address outside of your network. Using 64.7.161.12 (our Network DNS server) will be sufficient. See Figure A below for an example of a successfully traced route to www.yahoo.com. If you are not able to ping or tracert to any destination address beyond your computer, the problem is probably due to incorrect network protocol configuration.

Figure A:

4. NETWORK CONTROL PANEL SETUP: Depending on the network setup, the Network Panel should have either one of two configurations: DHCP or statically assigned addresses. If a server or the router is running DHCP then the Network Panel will be; Server Assigned IP Address, Use DHCP, No Gateway installed, Disabled DNS. This means that the computer is supposed to be assigned an IP address, Gateway, and DNS. To check if the computer is picking up correct information run 'winipcfg' from the 'Run' menu (only works on Win9x). On a WinNT or 2000 machine, run 'ipconfig' from the command prompt to check out the addresses.

5. IF CONNECTED THROUGH ONE CHANNEL ONLY: You will want to contact our Network Technical Support to check the integrity of your router configuration. If you have the password to a router that our Network supplied (probably a Netgear 338) than you will simply want to log into that router and verify that the SPID numbers for your ISDN lines are configured correctly. The same goes for if you purchased your own router. If the SPID numbers are entered into the router correctly, there is more than likely a problem with one channel on the ISDN line. In which case you would want to contact the provider of those lines for assistance.

6. SPORADIC PERIODS OF CONNECTION PROBLEMS: If you are intermittently having problems getting to websites and/or e-mail, try and log when problems occur. If they are predictable, i.e. happen during certain times of the day or, if the problem is totally sporadic. This could be caused by blatant over-utilization of available bandwidth or, a loss in ISDN signal. To check if it is a line problem, monitor the D-channel light when the outage occurs to see if it stays lit or dies. If it dies, you would want to contact your telephone company. If it seems to be a possible over use issue and the problems seem predictable follow the steps below.

The first thing you will want to do is run a constant ping on the router. This will help monitor the traffic to the Internet. Open the command screen (Start --> Run --> command [hit enter]). Type ping -t [router IP address] and hit Enter. The -t will force a continuous ping on the destination address specified, until Ctrl + C is pressed on the keyboard to stop the command.

If the connection problems are currently happening, watch the number of dropped packets (request timed out) and the number of returned packets. Watch the time in milliseconds (MS) that it takes for the returned ping requests (see figure A below). If the ping time increases sharply in a matter of 6 - 10 pings and then a “request timeout” appears, the culprit is most likely related to heavy usage on the network. This means clients within the LAN are using all their allotted bandwidth, and as a result, packets are dropped. Therein lies the cause of their sporadic connection losses.

Figure A:

If the periods of outage are totally unpredictable – the most common cause is the ISDN lines or the router configuration. Follow the steps above and do a continuous ping on the router.

If the connection problems are currently happening, watch the number of dropped packets (request timed out) and the number of returned packets. Watch the time in milliseconds (ms) that it takes for the returned pings to reach us (see figure A below). If you see that the “request time out” appears randomly with little or no increase in the ping times (see figure B), then proceed to trouble-shoot the connection starting on step 1.

Figure B:

IPConfig / WinIPCfg Explanations

The above DOS command is used to find LAN information such as:

Connection-specific DNS suffix - This is the specified domain of the resolving DNS server for a named network.

IP address - This is the address the computer is either statically assigned with, or the (Internal/Real) address the DHCP Server assigned it with upon initial LAN access.

Subnet Mask - This is the specified Subnet assigned to the local host which determines the size and/or class of network for the associated client IP address.

Default Gateway - This is the gateway IP address. This is typically the last hop a client IP address takes before reaching the outside Internet. If a DHCP/NAT server is running it will probably be the address of that server. If not, then a router IP address will probably be the assigned gateway address.

The commands ipconfig and winipcfg are the identical commands for different versions of Windows. The ipconfig command works on winME/2000/NT/XP. The winipcfg command is only used on win95/98. These commands are especially useful when trying to locate and test connectivity problems for dedicated customers or, customers running a Local Area Network. The information from this command provides you with the ability to determine whether the problem is related to internal IP/Subnet designation, or, with the gateway router/server. If the IP address is associated with an incorrect subnet, or, is on a completely different network as the other machines and router, it will be visible when running this command. This is also useful for when customers are unsure of the router address and configuration review/changes are necessary. The router will typically be the Gateway address listed by this command (but, can sometimes be a server).

Ping Explanations

The “ping” command is used to determine whether a specific address is available and properly responding to packet requests across a LAN/WAN. The ping command will respond with the following information:

"Reply from xxx.xxx.xxx.xxx: bytes = ## time<##ms TTL=### "

Reply - This is a response given from an IP address (the from address listed) that is correctly responding to a packet request. You will typically receive four consecutive replies that should all respond with relatively the same statistics. You can change the number of replies from four to continuous by including a ' -t ' after the first portion of the command. To stop pinging the IP address, simply hold the Control key down on your keyboard (Ctrl) and press the "C" key. See example below:

Request timed out - If a ping reply does not make it to the destination address, or fails to receive a timely (if any) response from destination address ("timing out"), it is safe to assume that there is a problem with the equipment configuration. The problem may also be a Layer 1 issue, which would include router hardware failure and all lines and connections between the ISP and the destination host (Repeaters/Smart Jack/ISDN/DSL/T1 lines/etc). See example below:

Destination host unreachable - If a ping reply responds with a "host unreachable" type error, it is probably due to some form of firewall or port block set on the gateway router or, before any destination address that you are trying to reach (be it a computer within the network). It could also be related to any form of routing issue (see trace route explanation). See example below:

Bytes - This is the amount of bytes sent in the ping packet (and can be changed for bandwidth/speed testing purposes). To change the amount of packets sent type a '-l' and the amount of Bytes you want the packet to include after the first portion of the ping command. See example below:

Time - This is the amount of time in milliseconds that the ping responded with. This is a "round-trip" time that the packet of information had traveled in. This information is important in situations when dedicated service customers report intermittent connection problems. Assuming that all other bases have been checked, you could run a constant ping to the your gateway address (typically a router) and have the ability to monitor traffic and ping times. If serious jumps in ping times are noticeable in situations where only a single computer is browsing, there is presumably some form of throughput issue causing the problems.

Trace Route Explanations

The “trace route” command is similar to a “ping” command. But, rather than simply checking to see if a specified address is responding, the command traces the exact path a packet of information would take to reach its host. This is especially useful for trying to diagnose routing issues and wide network outages. It allows a user to see certain “hops” to pin-point the exact location of where a connection has actually failed. Another obvious difference with trace route is that it does displays both IP address and Host name for each “hop” present in a packet destination path. As opposed to “ping,” which only does forward or reverse DNS depending on whether you ping a host address or an IP address.

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Last updated:February 17, 2004