Troubleshooting a “slow network” can be difficult since there could be many different culprits. One of the biggest challenges is that what someone describes as a “slow network” may not be anything directly related to the network.
If it is the network though, there are a number of tools in Auvik that can help narrow down your search to find the root issue and resolve it.
- Review alerts
- High bandwidth
- Packet errors
- Packet discards
- Broadcast storms
Auvik comes with many alerts configured out of the box, from informational all the way to emergency. Often these alerts shed some light on what’s going on. Review all the alerts that triggered in the hours leading up to and during the time the slow network was being reported.
Did a configuration change recently? Are you seeing high interface utilization on a specific interface? Is the firewall experiencing high CPU utilization?
Does nothing obvious stand out? Sometimes lower and slower network issues can fly under the radar. So next, we can jump into some of the other troubleshooting tools Auvik provides.
Check whether you’ve reached the bandwidth cap set by your ISP. Look at Aggregate Bandwidth Data on the home dashboard for this information. Remember you can look at live data from the past few minutes or examine historical data from when the slow network report was logged.
If you’re nearing the bandwidth cap, use the Top Interfaces widget on your core network switch to see which port is using the most bandwidth. Then look at the interface dashboard to determine which device is connected to that port until you find the culprit. We call this method “following the breadcrumbs.”
If didn’t get an alert for high bandwidth, it’s likely because Auvik is set to trigger on the interface negotiated speed and not the committed bandwidth cap set by your ISP. So now is a great time to set up a custom alert. See How do I add, edit, or delete alerts? for details.
When a device or port experiences packet errors the network can slow down because the device transmits the same information over and over, hoping the data will reach its destination without any errors.
Auvik keeps track of all packet error on all interfaces. You can see that information in the All Interfaces by Utilization report. There are multiple tabs so make sure you’re on the Errors tab. You can also sort by Transmit and Receive errors.
Once you verify a device or interface is experiencing packet errors, there are a couple of things to check, including Ethernet connections and access points.
Ethernet issues can include routers, switches, workstations, and NICs (network interface cards). Below is a partial list of problems that can cause packet errors:
- Bad CAT 5e, 6, or 6a cable
- Bad RJ45 connector
- Bad port on a switch
- Bad NIC on workstation or device
- Broken fiber cable
- Dirty fiber connector
- Bad GBIC or SFP module
- Interfaces not running in full-duplex mode
Access points are susceptible to packet errors. Since data travels wirelessly within a pretty congested RF range, there’s a higher chance of packet damage. If your access points are experiencing a high number of packet errors, check for RF interference. The problem could be anything from a nearby unmanaged access point, Bluetooth device, a microwave, or even spinning electrical machinery in a workshop. Also make sure your access point isn’t close to metal of any kind, such as cabinets or doors.
Set your SSID to the least busy channel. A Wi-Fi analyzer can help you with finding a good channel.
Just like packet errors, packet discards can cause devices to resend packets. Auvik also keeps track of packet discards on all interfaces. You can see that information in the All Interfaces by Utilization report.
Once you verify a device or interface is experiencing packet discards, there are a couple of things to check, including Ethernet connections, overloaded hardware, and access ports.
Ethernet issues can include routers, switches, workstations, and NICs (network interface cards). There are a number of reasons why a particular device or NIC is experiencing packet discards. Below is a partial list of problems that can cause packet discards:
- Interface loading: A 10 Mbit/s link trying to push 20 Mbit/s will discard half the packets until higher level protocols correct the transmission speed.
- Trunk port that should be an access port
- VLAN misconfiguration
Hardware problems can occur on network devices like switches, routers, and firewalls. If you’re seeing packet discards, here are few things you can check:
Just as with packet errors, access points are susceptible to packet discards. If your access points are experiencing a high number of packet discards, check whether your wireless clients are too far away from the AP or your transmit power is set too high.
A broadcast storm is caused by a flood of broadcast packets within a short period of time that get recycled around the network. A broadcast storm can overwhelm switches and endpoints as they struggle to keep up with processing the flood of packets. When this happens, network performance degrades at best, and in the worst cases, nothing communicates at all.
Auvik monitors the number of broadcast packets a particular interface is sending. You can see that information in the All Interfaces by Utilization report.
(For more information on broadcast storms, see How to Troubleshoot High Broadcast Utilization and Broadcast Storms on the Auvik blog.)
Find additional information at this link: SOP - Troubleshooting a Slow Network