The problem "only" occurred with IPv4 traffic - currently the most popular version of Internet Protocol and the one that is enabled by default on Cisco switches. Apparently, certain IP traffic sent to a Cisco switch can cause the switch to stop handling network traffic, in effect causing a denial of service.
What is unique about this problem is that, according to some experts, it only takes a few packets to crash the switch. And when it crashes, a manual reboot is necessary to get it going again.
Not only did this particular flaw affect almost every router on the internet, but many large businesses use Cisco equipment.
Think about this for a second: a single flaw in Cisco's IOS had the potential to bring down the internet and stop network traffic in many of the world's largest businesses. Clearly this is unacceptable.
Those who run the internet infrastructure, governments and network administrators in businesses need to assess whether standardising on Cisco is such a good idea. The IOS flaw has proved that Cisco's dominance in network infrastructure is unhealthy for the internet and for corporate networks.
The scale of the Cisco IOS flaw highlighted the need for suppliers to be accountable for bugs in their systems. Cisco has to prove to every user on the internet that such a problem will never happen again.
If the world was a fairer place, Cisco would be fined for the disruption it caused among internet service providers and businesses, many of which had to call network staff in to work evenings and over the weekend to fix the problem in the IOS software.