Mystery of slow and unreliable WiFi solved for Dublin accountancy firm

We recently assisted a Dublin accountancy firm with a slow and unreliable WiFi issue which was driving their staff to frustration. The WiFi network in their 8-seat office (where most users were connecting wirelessly) was performing sluggishly and the connection was intermittently dropping. In a busy accountancy practice, this was resulting in significant downtime, frustration and missed deadlines.

We went on-site to investigate. We asked the office manager about the background to the problem. They had first noticed the problem two weeks previously and the wireless network quality seemed to be deteriorating ever since. The building was divided into 5 different offices on three different floors. Our wireless site-survey revealed that the signal coverage in 4 of the offices was quite good. In the remaining basement office the signal was poor.

Diagnostics of wired network and access points

Firstly, we checked their Eir Huawei F2000 modem-router in their comms room and connected it directly to our laptops. It was getting fairly average upload and download speeds – 2.43Mbps and 17.83 Mbps respectively. A 24-port Cisco switch was connected to the modem-router and appeared to be working with no issues. They had 3 Netgear ProSafe access points which were located around their building. We logged into each one of these APs to check the data rates, channel settings and transmit power settings. They all had the latest firmware installed and appeared to be perfectly configured. The problem resided elsewhere.

Diagnostics with packet sniffer and problem diagnosis

Deploying a wireless packet sniffer called Wireshark we were able to analyse the data packet transmission on their network. This is a powerful piece of software which can see almost all network traffic on a LAN (local area connection) or WLAN (wireless LAN). Within 15 minutes, we started to see a second DHCP server appear on their network. A DHCP device is any device which automatically assigns IP addresses in a network. In the context of a SoHo (Small Office Home Office) network, there should only be one DHCP server and that function is normally assigned to the router. To confirm our findings, we logged into their Huawei modem-router again and disabled it’s DHCP functionality. As suspected, our packet-sniffer was still indicating an active DHCP service on their network. In short, there was a second router (or some other rouge DHCP server) on their network, which was causing this problem and we had to find it. Their friendly office manager recalled that two weeks previously one of their staff in their basement office brought in a device from home in order to improve the WiFi. This device sounded like the culprit. Back to the basement office and on top of a cabinet we found the source of the problem – a TP-Link router still connected to a network point.

Our solution to slow and unreliable WiFi issue

The TP-Link router was added to their network by a well-intensioned staff member who thought it might improve the wireless signal strength and connected to a an unused network point. But, in SoHo network design you should never have more than one router (DHCP server) on any one network because they conflict with one another. The solution was simple. We logged into the TP-Link router and changed it from “router mode” to “access point” mode. This turns off the DHCP service and turns off NAT in order to avoid a double-NAT problem. We then gave the device an IP address outside the range of their Eir modem-router in order to avoid any IP conflicts. Finally, we secured the TP-Link device using WPA2-AES256 encryption.

Solution Follow-up

On follow-up of the problem one week later, we were pleased to hear that their WiFi network is working reliably and smoothly. The basement office team member is finally getting reliable WiFi. The whole team was now able to enjoy fast, reliable and secure WiFi and able to file tax returns on time and. Moreover, the office manager no longer has to listen to moans about slow or unreliable WiFi from frustrated staff.