OzCableguy.com - Router FAQs

When speaking about computers, in layman's terms a Router is a device that goes in between your modem and your computer (or Network of Computers) and shares the Internet connection to as many computers as you like using a process called NAT.

There's barely a Router on the market now that is just a Router. Most have various extra hardware items & features built into them including:-

* Products are available overseas with built-in Cable modems, but they're no good here because the Cable ISPs only allow certain modems (that they supply) on their Networks.
Note: Products with built-in ADSL modems are unsuitable for cable and at this stage there is no such thing as a Router with a built-in ADSL modem that can be used for any other type of Internet connection other than ADSL.

Routers are secure, easy to use and reliable. A basic Router on a small Network will take an hour or so to install and keep plugging away happily for years. Attempting to achieve the same result with software methods can often take days (at the expense of much hair and sleep) and still be nowhere near as secure or reliable.
They can't be fooled by viruses or Trojan Horse programs, and because of the sheer number of different brands and models available, it's unlikely for anyone to come up with an exploit to affect them.

Simple Routers start from around $50.00 and go up as high as you like depending on the size of the job it needs to do, and extra features you may want or need. For the most part, the more you spend, the more you get. More expensive Routers are generally a lot more powerful to cope with larger sized Networks or more advanced Internet usage like multiple VPNs.

Generally, start with the cheapest products and compare them to the more expensive models or brands to see if the extra features and capabilities are worth the extra money for you, and then compare the various brands to each other and you'll usually find one that will stand out.

See my Find-A-Router tool for feature summaries, prices, ratings and links to manufacturer specifications, wikis, forum discussions and more.

You certainly can. I set up an online online shop at www.shop.ozcableguy.com specifically for this purpose where I have most of the best products available and can have them delivered usually within 24 hours.
Using a combination of working from a home office and a unique system called "drop shipping" (where goods are sent directly to my customers from the manufacturer's distributors) means that my overheads and prices are kept very low, while still being able to offer a reasonable amount of technical assistance as required.

Each PC will need a Network card and a patch lead. Patch leads, also known as Cat5 cable with RJ45 connectors, come in two forms - Standard and Crossover. Crossover cables are only used to connect 2 PCs together without a Router, or to uplink a Router to another switch (if no crossover port is available on either device). With few exceptions, the cables that go between the Router and the PCs will be Standard Cables (The Billion 711CE/7100Pro & Netcomm NB1300 are exceptions. These use a Crossover cable in the same situation.)
With Wireless Routers, you'll need wireless network cards for the PCs you want to be Wireless. Bearing in mind that most Routers with wireless capability also include a built-in switch so you can also plug PCs into it with cables and they'll all talk to each other exactly the same way irrespective of whether the PCs are wired or wireless.

When an ISP says they don't "support" something it doesn't mean it won't work. It just means that they can't (or won't) give you technical assistance to make it work. The last thing an ISP wants is to be put into the position of Network Consultant and then be sued for giving incorrect advice. Their responsibility ends at making sure your Internet Connection and any equipment they supply works.

Just about anything will work, as both of these game consoles have an Ethernet port* just like a computer and pickup the settings they need automatically from a DHCP server (the Router). Pretty much all you have to do is plug them into the Router using a straight through cable and away they go.
* Not sure if the PS2 comes with the Ethernet adapter or if you have to buy it separately.

Features to look for are UPnP support, and in the case of BigPond Cable, a built-in login client, particularly if you won't have a PC somewhere to maintain the Heartbeat.
XBox have published a list of Routers that do and don't work with XBox Live!, but you'll notice most of the products listed as not working have workarounds. In these cases XBox may also be being a little harsh on these products and they may have been listed as "bad" due to the manufacturer's implementation of the UPnP protocol and these Routers may work fine with a single XBox but may not work very well with multiple XBoxes on the same Router.
The same list will be fine to use as a guide for PS2s.

Although Microsoft have a Wireless adapter for the XBox, all you need for either the XBox or PS2 to connect Wirelessly is a "Wireless bridge" (in client mode) and a Wireless Router or Access Point that shares your broadband connection wirelessly.
Linksys have an 802.11G product called the WGA54G and D-Link have the 802.11G DWL-G810 at the time of writing. Most other manufacturers have a Wireless bridge/client of some sort that should do the trick fine. The open source Linksys WRT54GL also has some interesting possibilities in this regard with some of the firmware hacks getting around.
These wireless client devices will connect to just about any Wireless Router so it shouldn't matter if you need to mix the brands up. I set up a Linksys WET11 for a customer who already had a Netcomm NB3000 Wireless Router and the results were rather spectacular. Pings and throughput were fantastic with no noticeable difference from a cabled connection.

Sometimes a manufacturer will change some internal parts that will then require that different firmware version must be used. The version number of the product indicates to the owner which firmware version they need to use with their product.*
Sometimes these new hardware versions are released because of a short supply of a part, or because an alternate part can be manufactured much cheaper, and sometimes a new version will represent some improvements over the original. It's often difficult to find out which is which and quite often an older version will come back onto the market (eg if a supply problem with the original part has been fixed). In most cases it doesn't matter a great deal which version number you end up with as they all have pretty much the same performance and features but there are exceptions to this so it pays to do some googling to find out as much as you can about a product to see if there are any known problems with any particular version number.

*Warning: Uploading the wrong firmware version to your Router usually won't work but in some cases it will accept it and cause the product to fail.

In most circumstances, the default (DHCP) settings will do the trick. The PC's TCP/IP settings should be on all automatic and the Router will take care of the rest. See the Client PC setups on any of the guides. eg Windows 98/ME, Windows 2000, Windows XP.
Some Routers like Snapgears have their DHCP function disabled by default, so you'll need to configure your PC with the applicable Static IP or use the "Router Find" utility that comes with it.
Routers use the TCP/IP protocol for Internet Sharing which is universally supported by all types of Operating Systems including Macs, Linux, Unix and anything else around, so you don't need a Windows PC to use a Router. Routers are very popular with Macintosh users as they're usually a much cheaper and easier solution than most of the software applications available for Internet Sharing.

If you prefer to use Static IPs on your Network, all you need to do is find out the Router's IP address to use as a starting point. For example, if the Router has an IP address of 192.168.1.1, you would give your PCs IP addresses in the range of 192.168.1.2 to 192.168.1.254. (Be careful not to give any two PCs the same number, or to give a PC the same number as the Router or any other device like a Print Server).
Subnet can be the standard 255.255.255.0
Gateway is the Router's IP address - 192.168.1.1 (in this example)
For DNS Servers, if your Router has a DNS Forwarder you can use the Router's IP address as your Primary DNS Server, otherwise specify your ISP's DNS addresses here.
If your ISP uses unqualified Domain Names (eg if the name of their mail server is something like "mail", "pop" or "mail-hub" and not something that mentions the ISP's name in full like "mail-hub.bigpond.net.au"), then you will need to find out their DNS Suffix and also specify that in your DNS settings.
These TCP/IP settings are the same on all OS types but they may have slightly different names. eg Windows calls the DNS Suffix setting the "DNS Suffix" while Macintosh calls the same setting "Search Domains" on OSX, and simply "Domain Name" on OS9.

Yes, definitely.
If a Router is specified as having a number of ports (eg 4 or 8 in most circumstances), the Router is actually two different devices, a switch and a Router, joined together. A Router's built-in switch functions no differently to any other switch and will not hinder networking in any way. Actually, if anything, a Router will make networking easier as it can tell the PCs everything they need to know to join the network and access the Internet automatically.
As long as File & Printer Sharing, (aka NetBIOS over TCP/IP) is active and you don't have software firewalls installed, all you need to do is ensure that all of your PCs have the same Workgroup name specified and then you'll be able to see them all and browse their files by double-clicking the "My Network Places" icon. To access files on another PC, that PC first has to "share" the folder (or printer) to allow others to access it, and you do that by Right-Clicking on the folder or Printer and selecting the "Sharing" option.
If you get asked for a Password (XP & 2000 mainly) when you try to access a file on another PC, you'll need to also set up "User Accounts". See the Broadband FAQs for a tip on doing this.

While many routers now come with setup disks*, I strongly advise avoiding these and find out how to log into it using a Web Browser like Internet Explorer or Firefox. The manufacturer's Quick Start Booklet will tell you the address to type in (Usually either http://192.168.0.1, http://192.168.1.1 or http://192.168.1.254) and the default username & password you'll need to know to login for the first time. Once in there, there'll be a main setup section where you tell it your ISP type, username & password. They're all fairly similar in concept and here is what it looks like on a Linksys BEFSR41 V2

Note: It's the WAN (Wide Area Network, otherwise known as Internet) that interests us here. All that LAN stuff is fine to leave as it is unless there's some reason you need to change it, and then you'd only do so if you knew why you wanted to. Actually that goes with most settings you'll find in a Router. If you don't know what it's for, it'll be fine if you leave it as is. The manufacturers understand that most people wouldn't have a clue about half the stuff they put in there so they set them up so that they'll work properly by default and leave the other options for those that know what to do with them, or have at least read the manual.

* Setup Disks: These can be great but they're also responsible for a great deal of confusion and compatibility issues so use the web browser option instead if you can.

Firmware is the software inside the Router that makes it go. Much the same in principle to what Windows is to a PC.
Manufacturers issue updates from time to time where they add features, fix a bug or improve a security aspect. Generally it's a good idea to run the latest version, but the old saying "if it ain't broke, don't fix it" also applies. If something can go wrong with a Router, it'll often be during a Firmware upgrade which in some cases may involve sending it back to the manufacturer for repair.
Firmware upgrades can sometimes take a while and the Router can appear to have stalled in the process, causing many people to switch the power off and back on. This will usually have disastrous results by causing the Firmware to become corrupted leaving a Router that no longer responds to anything. In many cases there is a recovery process to revive them again but this can be a fairly complex operation that will be beyond the capabilities of many people.

NAT is "Network Address Translation" and is the method Routers use to share the Internet to multiple computers, and it also creates a fairly effective Firewall as a side benefit.
When anything connects to the Internet, the ISP will issue a unique IP address to it, whether it's a computer, router or whatever. IP addresses have different classes depending on whether they're for use on the Internet or for local internal Network use, and public (Internet use) IP addresses cost money.
What NAT does is allow multiple computers using internal class IP addresses to share one public IP address to access the Internet. The Firewall effect occurs naturally because any potential hackers scanning the public IP address can't see past it to any particular computer so they just bounce off the Router and get frustrated. In my opinion, NAT provides a sufficient level of security for most home users as it's effective, simple to use and less likely to conflict with recreational applications like online gaming and file sharing, but a Router for business use (or where there's particularly sensitive data) should have an SPI Firewall. Most recreational applications will also work fine with an SPI firewall, but they may require some effort creating the right rules to get them to work properly.

SPI stands for "Stateful Packet Inspection" and is a smart Firewall that can examine each packet of data, inbound and outbound, and automatically detect and block common forms of attack by hackers. Other benefits are that because of the extra attention to detail that an SPI Firewall provides, rules and filters can be far more comprehensive.
With just a NAT Firewall, a rule can be created to allow access by other Internet users to a particular PC on your Network through a particular port. With an SPI firewall the same rule can include limitations based on the source of the user, the time of day and which days of the week you want access to occur, and can also include similar rules for outbound activity. For example, this would allow a rule to be created that will prevent users on your Network from accessing FTP servers or even websites during certain periods of the day.

Content Filtering means blocking access to certain material available on the web, and will usually log attempts by Network users to access forbidden material. In most routers this is achieved by using either a keyword list, URLs or both. eg You can create a rule to block access to any website that uses the word "tree" in its name, or you can block access specifically to "www.tree.com.au".

Some can also restrict access to Instant Messaging, Peer to Peer applications and even block downloads depending on the file extension name (eg .exe) or even set these so they're only available during certain times to certain PCs on the network.

Other more expensive Routers can also have anti-virus capability built-in (with regular definition updates) and anti-spam.

Universal Plug and Play.
The name indicates this feature may be something to do with installing hardware but it's actually a smart network protocol that allows ports to be opened and closed on request. At the moment it is mainly used by MSN Messenger to allow voice, video and file sharing to work from all networked PCs at once without any special configuration necessary, but in the future it'll be utilised by devices like "smart" fridges so you'll be able to check your fridge at home from the office to see if you need to buy milk on the way home.
I find it to be a feature that is almost unanimously demanded by home & small office purchasers but it does have a few critics who think it adds some risk of being exploited by a clever hacker one day and/or MSN Messenger being use as a conduit to allow a virus into the Network. Nevertheless, the feature can usually be disabled in the Router by anyone who considers it a security risk.
See upnp.org for more.

VPN is Virtual Private Networking. This is a way for Computers in different locations to Network to each other using the Internet instead of a direct cable. VPNs are becoming increasingly popular with people who can't always be physically present at a PC that they need to access regularly. eg People who work from home or on the road that need access to a data file or email account at the office. Another popular one is using a VPN to remote control a PC across the Internet using an application like Timbuktu or VNC. Doing this sort of thing via a VPN is far more secure than just connecting directly using just a username and password.
Where VPNs can be a bit of a problem with Routers is because the Internet is involved certain security precautions are necessary and these have taken the form of different forms of data encryption. An unfortunate side effect of this encryption is that it isn't particularly NAT friendly and will usually either be blocked or restricted somehow by most Routers. To get around this, some Routers have built-in VPN Servers and clients, some have an ability to allow one (software) VPN tunnel to "pass-through" the NAT barrier and others have the ability to allow "pass-through" for several simultaneous VPN tunnels. One of the more common tales of woe I hear from people is where they've tried to save money and have purchased low-end Routers without considering their VPN requirements and for a few dollars more they could have had a more suitable product.

FAE from DrayTek Engineering Department warns that while Draytek Routers do have multiple VPN passthrough capability, not all VPNs can pass though the NAT barrier successfully: "there are many incompatibilities between NAT and IPsec: IPSec with AH can't passthrough NAT. L2TP with IPSec can't be passthrough NAT device except both VPN client and VPN server support NAT-Traversal mechanism. To the same destination, only one outgoing IPSec with ESP connection can be established at a time except both VPN client and VPN server support NAT-Traversal mechanism."

NETGEAR advises: "Most home router models support only a single outbound IPSec session. Some models provide multi-session capability, but this may not be sufficient in all situations.
The IPSec-passthrough ALG achieves its multi-session capability by using IKE cookies to distinguish IKE/phase1 sessions and the IPSec SPI pairset to distinguish between VPN/phase2 sessions. This differs from earlier ALG implementations which simply returned all IPSec traffic to the NAT client that last made an outbound VPN session.
It isn't possible to guarantee multiple simultaneous outbound sessions in all circumstances. For example:

These types of restrictions apply to the IPSec-passthrough ALG�s in most NAT routers, though it isn�t uncommon to find enough difference in the implementation detail between routers for some combination to fail on one device, work on another but to be the opposite for a slightly different case. There�s no easy way to be certain, without testing the customer�s specific case.
RFC3715 has a good discussion of why this is a complex problem to solve in the general case, and why it can�t be entirely handled in the router ALG, changes in the VPN software are suggested as well.
Some VPN implementations support NAT Traversal (NAT-T) which attempts to avoid the problem by re-encapsulating VPN traffic inside UDP packets which allows them to be better handled by NAT routers. For this to be effective, both the VPN server and client software need to support compatible implementations of NAT-T. In some situations it may be possible to use a VPN endpoint router in place of the software VPN client - a single tunnel between the client-side router and the VPN server may then be able to accommodate multiple client sessions to the same destination."

Port forwarding, also known as Virtual Servers, is a way of directing traffic from the Internet through the Firewall effect of NAT to a particular PC on your Network that you want people out on the Internet to be able to get to. Typical examples where you might want to do this include running your own website, remote control applications like PCAnywhere, webcams and running your own Game Server.
Data travelling across a Network (or the Internet) uses a combination of protocols and ports, and Computers have 65535 ports (ie possible end points or destinations). A lot of these port numbers have common uses and are assigned by the Internet Assigned Numbers Authority. In particular, ports 1 - 1024 are known as common ports, and within this range you'll find most port numbers used in day to day Internet and Network browsing. For example, Websites use Port 80, FTP is port 21, Send email (SMTP) is port 25, NetBIOS (File and Printer Sharing) uses port 139 and the list goes on.
What happens with NAT is when data is travelling to your PC (as opposed to outbound), it will hit the Router on a particular port number and will have nowhere to go. This is generally a good thing as it keeps the hackers out, but there may be situations when you actually want that data to find it's way through the NAT layer to a PC, and that's where Port Forwarding comes in handy. We can tell the Router to accept that data and direct it to the PC we want it to go to.
As an example, lets say we wanted to run a Website from one of the PCs on a network. We know websites use Port 80 and the PC is on Internal IP address 192.168.1.4 (See the glossary for how to find out the IP address of a PC). So now all we have to do is tell the Router to "route" all Port 80 traffic that comes in from the Internet to IP address 192.168.1.4 on our Internal Network.
This is what it looks like on a Linksys BEFSR41 Router -

And this is a Billion 741GE -

Note: Port 80 is one of the standard options on the Billion. For a non standard port there are blank options further down the page where you can also specify a whole port range instead of just a single port and the full range of protocol options -

With some Routers, the port number is selected from a pulldown list with standard port numbers available. If the port you wish to use is not in the list, you'll need to find a section in the Router where you can add a "custom virtual server" and then it will appear. Other Routers like the Alcatel Speed Touch Pro also require specifying an "outside address" (the IP address someone the Internet is connecting from). In these cases you'll probably want this open for everyone so specifying an address of 0.0.0.0 usually does the trick.

For information about a specific application, Google the name of the application and the words "Firewall" and "Ports" and you'll usually turn up everything you need. Often adding the name of your Router will find even more specific information.
A fantastic resource with specifics for dozens of Routers is PortForward.com.

Most Routers include a built-in DDNS client. See the Remote Access page for more about DDNS.

Most Routers keep logs of all kinds of activity both inbound and outbound. Some, like most Netgears, can be configured to email the logs to you at specific intervals or when certain types of activity occur. Other Routers like Linksys and Netcomms have an external application (downloadable from the manufacturer) that collects the log data from the Router and displays it in various ways. (For these types of Routers there will be a page where you can turn logging on and specify the IP address of the PC running the logging application). Other people have written their own versions of these logging applications that can display the data in lovely graphs and tables.
See Wallwatcher for Linksys
Linklogger for Netgear, Linksys & Zyxel.
Trev's SNMP utility for Billion 741GE.
Trev's D-Link DSL500/504 info dump
And there's probably heaps more of these around too for other products.

Some Routers' Internet connection types like BigPond Cable have an idle timeout setting. This is supposed to instruct the Router to disconnect from the Internet if no one has used it after a certain amount of time and then reconnect automatically as soon as someone tries to access something again. Personally I can't see the point and this feature has caused so many problems for so many people I'd prefer to see it omitted completely in favour of an "always on" connection. After all, we're not charged by time on Broadband so what's it for?
Furthermore, this feature can cause some truly evil behaviour on some Routers. With Netgears for example, we used to be instructed to set the idle timeout to "0" for an "always on" connection, but now with many models, setting this to "0" causes the Router to constantly connect and disconnect in under a second. (Aargh!). Even worse is that these same models still instruct to set Idle Timout to "0" for an always on connection in the help files.
Linksys are worse again (Termed "Keep Alive: Redial Period xxx seconds" or similar). Setting this field to 0" will often cause the Router to go into a perpetual reboot sequence which is not recoverable or reversible so it has to go back to the factory under warranty.
Your best option with Idle Timout is to set it to 30 mins regardless of what the manufacturer's instructions say.

A quick warning on Power Buttons.
Power buttons are quite often a weak link on this type of equipment and are one of the key areas of failure second to firmware corruption. In most cases you're better off not touching them, but if you do feel the need to switch your Router off on a regular basis it's best to switch it off at the power point or even pulling the power out of the back.
Most manufacturers have omitted power buttons from modern models because of this problem. Hey, warranty claims cost money that has to be factored into the production cost, so if you can eliminate 20% or more of them by leaving out a dodgy 15 cent switch, it makes perfect sense.

Some routers have ports to allow them to be connected to more than one modem. These products are often termed multi-WAN routers and when they can be connected to more than one ISP simultaneously you have an aggregated connection. But there's a catch: You cannot combine multiple broadband connections to create one super-fast connection as such. What you can do is "load share" or "failover".

Failover means if one Internet connection goes down it will automatically switch to the other.

Load share means it distributes the available bandwidth evenly between the connected users depending on demand. For example, with all things being equal such as 10 users on a LAN connecting to multiple servers all capable of delivering full download speed and you have 2 x 1500 kbps Internet connections, each user will get 300 kbps download speed. In other words, each user gets much faster downloads than they otherwise would have with just 1 x 1500 kbps connection. However, the fastest any one user will achieve with still be 1500 kbps. You cannot combine 2 x 1500 kbps broadband connections to create one 3000 kbps connection as many people expect. Now, with dial-up and ISDN you can combine multiple modems to form one faster connection using Windows Multilink (or various open source solutions) and an ISP account that supports it but as far as I'm aware there's no such option with Cable, ADSL or 3G, at least not in Australia*.

* Update (June 2010): Zyxel have released the P-663H-51 ADSL 2+ Bonded Router which does do ADSL2+ port bonding. However, you still need an ISP that supports it, and iinet has just started offering a bonded DSL service in Australia.

An easy way to find multi-WAN routers is to use the Find-A-Router section where there is an option to select routers with more than one ethernet WAN port. However, there are also other variations in multi-WAN routers. Instead of two ethernet WAN ports you might find products with a built-in ADSL modem and an Ethernet WAN port and/or a USB port for a 3G modem and so on, so you'll need to select different options to find these such as ADSL modem + Ethernet WAN port, or ADSL modem + 3G USB port, or Ethernet WAN port + 3G USB port, and so on.

Watch the cheaper stuff: While most multi-WAN routers have failover or loadshare capability, some will only have failover and some will not do either and can only be connected to one ISP at a time. Usually the cheaper the product, the less likely it is to have loadshare and/or failover, or the less creative you will be able to get with how the bandwidth is allocated so read the fine print or talk to the manufacturer or seller when in doubt.

There are three main reasons for this -
1. The PC is not getting an IP address from the Router. This can be because the PC is configured with a static IP address in an incorrect range, the Router's DHCP server is not switched on (Usually a reset via the reset button will fix this but some Routers like Snapgears have DHCP off by default), or the PC has not had a chance to renew it's IP address. See the glossary for how to force this to occur.
2. There is a Proxy Server specified in your Internet Options.
Go to Control Panel > Internet Options > Connections and set to � never dial�

Go to Control Panel > Internet Options > Connections > LAN Settings and untick all the boxes.

3. There is a faulty or incorrect cable type being used. Check that link lights on the router are coming on to indicate a valid connection between your PC and the Router.

Many ISPs use "unqualified domain names". This will usually be the case if the outgoing (SMTP) mail server in your Email account settings doesn't have the ISP's name in it somewhere. For example, BigPond Broadband uses "mail-hub" while the fully qualified domain name is "mail-hub.bigpond.net.au".
To get around it, you will either have to add the rest of the domain name or add a special DNS suffix to the TCP/IP settings on your PC.
See the Broadband FAQs for more help with email problems.

The most common reason for this is when your ISP uses a PPPoE or PPPoA connection type (most ISPs that support one also support the other so it doesn't matter which you choose) and you don't add the full username. In almost all cases, the user name will be "username@something" and not just "username". eg BigPond customers use username@BigPond, Iinet customers use username@iinet.net.au and Internode customers use username@internode.on.net. Notice that the last bit varies between ISPs. Some, like BigPond, just require @bigpond and nothing else or it won't work, whilst Iinet needs the .net.au bit as well.
Update: I recently hooked up a BigPond customer and only "username" by itself would work. The usual "username@bigpond" format just plain refused to connect, so if you're having trouble connecting you should definitely try a few variations along these lines.
Optus ADSL is a little peculiar and deserves a special mention too. Most ADSL modems have a setting in the advanced section for the "Authentication Protocol" to be used. By default this will usually be set to something like "PAP/Chap" or "Chap (Auto)" but these don't work with Optus DSL. It must be changed to PAP only.

Another common reason when using ADSL modems like the Billion 711CE/7100Pro or Netcomm NB1300 is that these require a crossover cable to connect to a PC or another Router. You'll spot this right away as the link lights won't be lighting up if you've got the wrong cable type.
For other ADSL types that use variations of IPoA (like TPG), if you're not sure which encapsulation type to use, just try every option that doesn't require a username and password and check the Router's status page with each attempt until you get it.

Another one that frequently comes up is where there is a fault on the ADSL line or the exchange. These ones will be obvious in that the Line Sync light will not be showing a "sync" status. Generally a proper line sync will be shown by a solid glowing sync light on the modem, but some oddball modems may show a line sync as a blinking light. For example, some firmware versions of Dynalink RTA100 & 220 show a blinking light, but to add a spanner in the works, these same products when upgraded to more recent firmwares will show a solid light.
In my experience connecting ADSL whilst working for Telstra, when line sync problems came up, the rate of faults in the line or exchange Vs actual faulty modems was around 100 to 1, so the chances of having a faulty modem in these circumstances is fairly small (particularly if you can log into it and everything else seems to be functioning properly). However, it still happens, so if the ISP is going to charge you a service call to inspect the line where no fault is found, the only way you can double check your modem is by plugging it in at a location where the ADSL is known to be working, or borrowing a proven modem and plugging it into your phone line.

If your router is completely locked up (sometimes called "bricked" because it's now only useful as a doorstop) all may not be lost. This is quite often a case of software corruption rather than a hardware problem and some products can be fixed without sending it back to the manufacturer.

The first thing to try with any product is to stick a paperclip into the reset hole on the back until you feel the tiny button and then hold it down for 10-20 seconds or until you see a flicker or some other response in the lights on the front. Give it a few seconds and then power it off and back on.
Tip: If the reset button doesn't appear to be working, one trick that sometimes works is to hold the reset button down while powering the router off and on a few times in quick succession.

If a reset doesn't fix it, some manufacturers have recovery tools available for this situation:

Many modem/router products like the Netgear DM602, Billion 5100 & 7100Pro, Dynalink RTA100 and others are commonly purchased to be used with other Routers and also many people may have existing modem/routers that they want to use with different Routers (eg Wireless Routers). What we need to do here to get the best results is to change these products to behave as standard modems (called "bridging") and not behave as Routers any more. The reason for this is that having two Routers inline isn't a good thing to do and while usually you'll get things working this way, it becomes very difficult to configure other services through and you could also create a bottleneck in the data flow. (Something you particularly want to avoid if you're plugging a basic modem into an advanced multi-VPN Router for example, as you'll lose all the advantages the better Router has to offer).

The first step is plug the modem directly into a PC. (If you plug it into the Router you're going to be using you won't be able to access it to change the settings).
Next, follow the manufacturer's instructions to set up your PC to log into the modem's configuration menus.
Look for an option in the menus (Usually under "setup" or "quickstart") where you can change it into a "bridge". Depending on the product, you may also have to adjust the encapsulation type to match. eg. It may have an option that says "Bridged IP LLC" or "RFC1483 Bridge" and other similar derivations.
Other details like usernames and passwords leave blank, and uncheck any options to "dial on demand" or "automatically reconnect".
Save the settings and Bob's your Uncle. You can now plug the modem into the Router and set the Router up to login into ADSL using a PPPoE ISP type.

Bridging instructions are usually found within the modem's manual, but these links may help.

Note: Most ISPs are LLC based and use VPI of 8 & VCI of 35, but check with your ISP if unsure of these parameters.
Note2: Some people worry about the old modem/router being on a different IP range or even being on the same IP address as the new Router. The IP address used by the modem/router in bridging mode doesn't make a lick of difference and won't conflict, so there's nothing to be considered there. In bridging mode, the modem doesn't have an active network presence so it's invisible to everything on the LAN anyway.
Note3: If your old modem/router has 4 ports, Internet Sharing will no longer be available from these extra ports once it's in bridging mode. Your PCs will need to be plugged into the new Router for this to happen.

Another way to do it is allow the modem to perform the authentication but switch off NAT (sometimes called "half bridge"). Then set the Router up as a Connection that doesn't require a username & password (Dynamic ISP). This technique comes in handy if your ISP uses a PPPoA authentication type but your Router only does PPPoE and it won't work (often it will work anyway, so give it a try first).

Note: If you're bridging a router/modem to another Router and can't seem to connect, plugging the modem directly into a PC and configuring a software connection method can reveal some useful error messages (if it won't connect that way either of course. If it does, you know something's amiss with the Router configuration).
"Authentication error", or "username/password is invalid on the domain" type messages are incorrect username and/or password problems. (Be aware that sometimes these happen because the ISP hasn't properly activated your account or they've given you incorrect details or a typo)
"The remote computer did not respond" indicates the modem is not bridged correctly or a line or exchange fault exists. Sometimes phones and other devices plugged into the same line without filters can cause interference to the modem too.

1) Viruses & Malware. A surprisingly common reason is infection by certain viruses. See my blog entry referring to Welchia virus. Another common one a few years back was SDBot but there's plenty that can cause this problem. These viruses will flood a router with so much traffic that it will cause the router to lock up or reboot giving the false impression that there's something wrong with the router. Netgear released a news bulletin about it when the first of these started to pop up.
Don't always trust your anti-virus software either. I have seen first hand on several occasions Welchia or SDBot have been rampant on PCs running up to date versions of common anti-virus products, and I have even seen SDBot infect a PC within minutes of going online after a format and clean installation. The best way to check is to install a network analyser like the Commview trial version and check for large amounts of unusual outbound activity.

2) Outdated or Corrupt Firmware Versions. Instability can be a problem on many Routers with some of their initial firmware releases. Upgrade your Router to the latest Firmware available and see how it goes. Corrupt firmware may also sometimes be less than obvious. If your router used to behave fine but recently started playing up then download and install (or reinstall) the latest firmware, perform a factory reset then reconfigure from scratch. (Don't use a backup configuration file in this case. Always manually configure it)

3) Processing Power. Your Router may not have the processing power for what you're asking from it. Routers below say $150.00 are designed for basic home networks of 5 - 10 users as a rule and the cheaper the product the less likely it'll be able to perform well under busy loads. For larger Networks, or where there are busy servers present, throughput figures become very important and more expensive products become the cheaper solution in the long run. (Big dollar products usually means lots of processing power.)

4) Torrents. Related to point 3 above is using file sharing applications like BitTorrent. Most torrent clients by default don't restrict the number of current open connections and this can quite easily fill up a Router's NAT table within a short period of time and cause poor performance or frequent lockups or reboots. If you're into these things make sure you do your homework first by searching the BitTorrent forums to find which Routers cope the best. Alternatively I believe some clients have an option to restrict the number of active connections in their advanced options and this will generally cure the problem too as far as I'm aware.

5a) Cable Internet. If you're on Cable Internet, check that it is correctly configured and that you have the correct type of Cable modem to plug into a router per the "Connecting Routers to Cable ISPs" FAQ.

6) ADSL Filters. ADSL modems often drop out due to problems with the phone line or inadequate filtering allowing interference from other devices such as a Foxtel IQ box. See ADSL FAQ 1.6 for more about line filters.

7) ADSL Line Quality. Your modem's ADSL status page can tell you quite a bit about your line quality. Phoneworks have an excellent breakdown of what's good and what's bad when looking at these figures:

Line Attenuation
20bB. and below	Outstanding
20dB-30dB.	Excellent
30dB-40dB	Very Good
40dB-50dB	Good
50dB-60dB	Poor and may experience connectivity issues
60dB and above	Bad and will experience connectivity issues

SNR (Signal to Noise Ratio)
6bB. or below	Bad and will experience no line synchronisation or intermittent synchronisation problems.
7dB-10dB.	Fair but does not leave much room for variances in conditions.
11dB-20dB.	Good with little or no synchronisation problems
20dB-28dB.	Excellent
29dB. Or above	Outstanding

Here is where these figures can be found on a Draytek modem -

On Billion modems these are usually found in the web interface under Advanced > Status > ADSL Status.
Other manufacturers follow a similar pattern and will be under a "status" page somewhere.
Note: SNR may be referred to as "Noise" or similar on some products, and where figures for both upstream and downstream are displayed all figures need to be taken into account.

If you have a poor SNR figure (6 or less) the first thing to check is if the fault is on your premises. To find that out perform a Line Isolation Test. If that makes no difference it's most likely a fault on your telephone line in between your premises and the Telephone Exchange so consult your ISP*.

* ISPs are notoriously reluctant to organise a technician to check the line because it costs them money whether a fault is found or not so it may often take some negotiating to get the problem fixed. They may also recommend a change of profile (ie sacrifice some performance for stability) which is often an acceptable workaround.

Tip: If you're still unsure whether a fault lies with your modem or with the ISP or the phone line, the only way to be sure is to try another modem or try your modem at another location that is known to be fine.

8) Faulty UPS or Power Board. A fairly rare one but one that does come up occasionally is problems with uninterruptible power supplies (UPS) and/or surge protectors. If your router is plugged into one of these and you're having lock up or rebooting issues, try bypassing the UPS or surge protector to test if it's the culprit.

There is some variation with how various modems report their sync rates so it isn't always a reliable figure to judge a modem's performance by. A better test, if you have one modem reporting a faster sync rate than another, is to perform a download test from a known good download source.

Also, some modems may prove to handle poor line conditions better than others. For example, modems with Broadcom chipsets are known to be more stable under poor conditions while other chipsets are more performance orientated and may drop out from time to time under the same line conditions. However, this is not necessarily the modem's fault and even if you do find one modem more stable than another you're probably still losing performance so it pays to check your line conditions (see point 7 in the FAQ above) and talk to your ISP as necessary to address the problem.