With more and more of our documents cloudbound, failure of an Internet connection can spell disaster. Do you give up and chat, read a book, or what?

Internet connections are getting more reliable, but there is always the rogue worker who cuts through fibre-optic cables with a drill, the winter storm that brings down overhead cables, or remote hardware failure. However it might happen, a little bit of forethought and planning can save you from the cost and frustration of complete blackout.

The most important information that you must keep to hand is how to contact your ISP in the event of a service interruption. Keep that updated from their support pages. If those only provide online methods of reporting the fault, search those pages until you find a phone number.

If you are dependent on an Internet connection, and outage will cost you money or cause serious problems, you must plan an independent secondary connection which you can fall back on. For low data volumes this could readily be a reliable 3G cellular phone service, perhaps using a ‘MiFi’ point to support a Mac or two and iOS devices. For heavier use a second full broadband connection is invaluable, and need not be too expensive: a SOHO business package might be sufficient.

You can run two or more modem-routers on the same network by assigning them different IP addresses, such as 192.168.1.253 and .252, and configuring each networked device to use one of those as its router. However you must set them up so that only one device provides DHCP, or mayhem will result, with different devices being assigned the same IP address by a different DHCP server. Make each modem-router setup a separate location, and switching from your primary to secondary connections will take but a few seconds.

ISPs sport detailed service status reports which are often misleading or out of date. If no fault appears listed for your area, do not assume that it is your modem-router or local network that has gone down, but check your end carefully to rule those out. Remote line checks can fix issues quickly, but may be surprisingly slow and uncommunicative.

Be prepared for spurious errors, perhaps being diverted to a website which claims that you have been disconnected because your account is in arrears. However it is wise to ensure that there is no truth in that suggestion!

Basic steps to verify that the fault lies in your connection and not your Mac, modem-router, or local network begin with you restarting your modem-router and Mac. If this does not restore normal service, try connecting with another device, such as your laptop or iPad.

Connect your Mac direct to the modem-router using a trusted Ethernet cable, and check the connections between the modem-router and service socket. Replace any broadband filters along that path, and prune all devices other than your modem-router. If it is connected to the line that provides voice phone services, check that they are working correctly; if the whole line is dead, report that as the top priority.

Sometimes only certain services, such as outgoing email or HTTP/HTTPS connections, are lost. Once you have restarted your modem-router and Mac, check that the faulty services are not being blocked by a firewall or other configurable filter within your local network.

Painfully slow connections to your ISP’s servers, that fail altogether when you try to go further, are a good indication that your ISP has either inadvertently limited your service, or their servers and connections are at fault. There is then little more that you can do other than wait for them to fix it. Provided that you have planned for that contingency, that wait should be but an inconvenience, not a disaster.

Tools

The most useful tools for diagnosing Internet connection problems are built into Network Utility, oddly hidden in Mavericks and Yosemite. Look for this in /System/Library/CoreServices/Applications, create an alias to it, and put that alias in your Applications folder. Do not move the original app, as other OS X features rely on it being where it is.

The Ping pane is an important test: set this to ping a major server such as http://www.apple.com or one of its related IP addresses of 92.123.184.211, and you should see three prompt replies; if the IP address works but the domain name does not, you have a problem with DNS resolution. If both work fine but other services such as HTTP do not, suspect that your ISP is throttling certain network traffic only, because of server failure or misconfiguration.

Traceroute is valuable for explaining slow ping responses, as it shows the intermediate servers between you and a remote system. This can, for example, discover switching problems in your ISP’s hardware, if your packets are sent round many intermediates before reaching another country.

There are also fancy graphical versions such as WhatRoute which help visualise where delays are occurring. Avoid unnecessary tests and never use PortScan unless the operator of the system you are scanning has given you permission.

Updated from the original, published in MacUser vol 30 issue 08, 2014.