Month: November 2012

Find unknown static IP on device

If you work in networking sooner or later there will be a situation where someone will bring you a device that you must connect to your network that was used somewhere else before. That can be something like switch, Fiber channel switch, some security appliance, different controllers etc. In that case this device will often have a static IP address assigned and you will not know whish address that is. In that case you are unable to communicate with the device and if you are connecting it to your network he will have different IP from you subnet. That will make the device unreachable.

You need to find this unknown IP address in some way so you can connect to the device and then change the IP.

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SAP – Session Announcement Protocol

Session Announcement Protocol as an experimental protocol designed for the purpose of multicasting a session’s information. IETF issued it as RFC 2974. SDP (Session Description Protocol) is being used by SAP as real-time transport protocol’s session depiction arrangement. With SAP use, correspondent can transmit SDP descriptions from time to time to an acknowledged multicast address and also to port.

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Recovery From Corrupt or Missing Software Image on Cisco device

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…

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Unidirectional communication filter between two VLANs

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.

UPDATE on 01 Sep 2017:
This article is about reflexive access-list which enable some sort of false statefulness for TCP traffic going through your router. After some feedbacks from my readers, I wrote another, a bit better article about reflexive access-list configuration so I suggest reading the other one as well.

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. 

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