Author: Valter Popeskic

This is a movie based on a true story. Is the issue you will have sooner or later if you are into networking and managing devices? Perhaps you will manage to upgrade hundreds of devices before you will see this happening but maybe it will be one of the first devices in production environment to go down exactly when you don’t have time for this kind of problem. Better be ready and read next short story about how is possible in very short time to revive a dead device stuck without IOS Software on it.

If you have a corrupt or missing software image on Cisco device this is the thing you should do:

Reset to the factory default using Mode button if you have the Mode button, if your device is not having that button then simply reboot the device and hit break or Esc key to stop the booting process. In this example, again, based on my true story I will take an example with recovering one of standalone Cisco Aironet Wireless Access points. It’s basically the same with all IOS devices and some devices that do not have IOS but some older software and then you want them to upgrade to IOS. It’s for example the situation with one very old Cisco Aironet AP350 device. Let’s go…

Block Traffic among two VLAN’s but only in one way, how to do that?

VLAN and VLAN configurations are very useful in all kinds of different ways. This configuration will be useful sooner or later for all network administrators out there.

It was a big challenge to resolve this tricky communication security requirement. The problem actually does not seem like a big deal but when you try to make it work you see that it is.

The goal was to make unidirectional communication filter between two VLANs. The request was to allow VLAN 10 to access VLAN 20 but not the opposite. The computers from VLAN 10 needed to access resources in VLAN 20 normally but computers from VLAN 20 had to be prevented to access VLAN 10. 

Sytek Inc developed NetBIOS in 1983 as an API (a specification proposed for using it as an interface to communicate by software parts) for software contact over IBM PC LAN networking technology. The Network Basic Input/Output System (NetBIOS) was at first introduced by IBM (a company, which is running IT consultation and computer technology business to access LAN resources. Since its creation, NetBIOS has developed as a starting point for a lot of other networking applications including International Business Machines, for example: Sytek (API). This Basic Input/Output system serves as an interface specifications to access the networking services.

The response and prevention

In order to defend against Denial of Service attacks the combination of attack detection use is typically involved in it, classification of traffic as well as response tools, and the target is to block traffic if identified as illegal and permit the legal traffic only after identifying it. Below is a list of response tools as well as prevention:

Firewalls

The rules of firewalls are quite simple like to permit or not to permit ports, protocols, or IP addresses. There are some DoS attacks that are quite complicated for number of firewalls, for example if an attack occurs on port 80 (web service), it is not easy for the firewalls to differentiate between the bad traffic and the good traffic of DoS attack so the filter packet filter firewalls cannot prevent the attack. In addition, firewalls may be located too deeply in the network. Even before the traffic enters the firewall the affect on routers may take place. However, firewalls can play an effective role in preventing users from the launch of even simple flooding attacks that can occur from the machines behind the firewall.

A PDoS or permanent denial-of-service, also referred to as phlashing, is a severe attack that completely damage a system as a result of which the system’s reinstallation of hardware or replacement is required. A PDoS attack exploits the flaws of security which further permits the administration present far away on the hardware of the victim management interfaces, like printers, routers, or other hardware used for networking.