| 1. | Configuration not saved
Reboot will cause config to be lost
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| 2. | Saved configurations don’t meet corporate policy
Source of many problems from performance to reliability to security
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| 3. | Bloated firewall rule set; unused ACL entries
Poor firewall performance
Open, unused rules, creating potential security problems
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| 4. | Firewall connection count exceeded
New connections via the firewall fail
Business applications exhibit intermittent failure at high firewall loads
VPNs begin to fail
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| 5. | Link hog - someone downloading music or videos
Slower application response, impacting user productivity
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| 6. | Interface traffic congestion
Unpredictable application performance, impacting user productivity
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| 7. | Link problems & stability
Physical or DataLink errors cause slow or intermittent application performance
Link or interface stability can impact routing and spanning tree (see other examples)
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| 8. | Environmental limits exceeded
Fan failure, power supply problems, and high temperatures are indicators of problems that will likely cause a network device to reboot, affecting any applications relying on the device
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| 9. | Memory utilization increasing
A bug in the device’s operating system is consuming more memory and when no free memory exists, the device will reboot, disrupting applications that are transiting the device
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| 10. | Incorrect serial bandwidth setting
Causes routing protocols to make non-optimum routing decisions
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| 11. | No QoS
Important business applications are not prioritized, yielding unpredictable or poor performance during times of interface congestion
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| 12. | QoS Queue Drops
Important business applications are slow
Business needs may have changed since the queue definitions were created
VoIP is especially affected by this problem
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| 13. | Route flaps
Poor application performance as packets take the wrong or inefficient paths in the network
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| 14. | OSPF recalculations high
Routing protocol unstable; poor and inconsistent application performance
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| 15. | Poor VoIP quality
Due to high jitter, delay, or packet loss
Choppy voice calls
Calls mysteriously disconnect
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| 16. | Routing Neighbor changes high
Applications using paths via this router will be unstable or slow
Affects OSPF, EIGRP, and BGP
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| 17. | OSPF area not connected to backbone
The disconnected OSPF area will not be reachable from other OSPF areas, impacting applications that need to communicate between areas
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| 18. | Unidirectional traffic flow
Typically the result of misconfigured routing
Slower applications, strange failure odes, and complex troubleshooting due to asymmetric routing
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| 19. | Router interface down
Any router interface marked administratively up but is operationally down is likely to be a redundant connection that will cause an outage if the other connection also fails, affecting all applications that use it
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| 20. | Unstable root bridge
Bridge priority not set; applications quit working over unstable VLANs
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| 21. | Duplex mismatch
Increasing link errors
Applications get slower as traffic volume increases
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| 22. | Downstream hub or switch
Unauthorized devices added to the network
Compromise to network integrity and security
See 20, Unstable Root Bridge
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| 23. | Port in ErrDisable state
The set of end stations connected via this port are disconnected from the network until the port is enabled (either automatically or by user control)
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| 24. | Unbalanced & unused etherchannels
Increased latency & jitter affecting sensitive applications like VoIP
Compromised redundancy
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| 25. | HSRP or VRRP peer not found
Redundancy configured and not operating correctly
Outage when a second failure occurs
Redundancy compromised
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Free Poster: The above network problems are available as a snazzy FREE poster (ordered mine) that is suitable for office display and framing, it details the top 25 network problems that Netcordia's NetMRI detects. It's a great resource for communicating between managers and technical staff, as it illustrates the business impact of common network problems. Receive your free poster
Related story:
The major cause of failures are fingers
What do YOU think is a top network problem?
