Several internet lines and still slow: five things to check

Many offices answer slow internet by adding another line. Then a third. The bill grows and the complaints stay.

In a recent job for an office of about 75 devices with four internet lines, one line was carrying 51 Mbps while two others sat almost idle. After the changes below, the same lines delivered more than 112 Mbps across three of them. No new line was bought. Read the full case study.

These are the five things we check first.

1. Is the load actually shared?

Lines plugged into the router are not the same as lines being used. A common setup assigns each device to one line, once, based on its address, and keeps it there. If the rule only knows about two lines, the third never carries anything. If a few heavy users land on the same line, that line fills up while the others wait.

Look at the traffic on each line during a busy hour. If one is full and another is quiet, the problem is the balancing rule, not the lines.

2. Is each line weighted by what it really delivers?

Providers sell "up to" speeds. Measure each line yourself, at the time of day that matters, and give each one a share that matches what it actually delivers. A line that gives half the speed of the next one should carry half the traffic.

3. Do bank and government logins keep dropping?

Some sites tie your session to the address you logged in from. If balancing sends the next request out of a different line, the site sees a new address and logs you out. Pin those destinations, such as banks, tax and government portals, to one line, and balance everything else.

4. Is the router itself overloaded?

"Connected, but nothing loads" is often not the provider's fault. Check the router's processor and its list of running jobs.

In that same office, a scheduled script hung instead of finishing. It was our own speed-test script. Four copies piled up over four days and held the processor at 100%. Stopping them brought it down to about 50% straight away. We then made every scheduled job clear its leftovers before it runs, and added a watchdog that reports anything still running from a previous day.

5. Does bandwidth control cover every device?

Per-device limits stop one large download from starving everyone else, but only for devices inside the rules. We found 41 devices that had slipped outside them; after the fix there were none. New devices, phones and anything with a fixed address are the usual gaps.

While you are in there

Two things turned up that had nothing to do with speed: an administrator password stored in plain text inside a router script, and copied into every configuration backup, and a nightly router backup that had quietly stopped working weeks earlier. Both are worth checking on any network that "has always worked".

Is your office internet slower than the lines you pay for? Send us the details and an engineer will reply within one business day.