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I have small system with the following IP's from /etc/hosts file machine1 machine2 machine3 machine4

the system connected to Cisco switch ( I dont have access to the cisco SWITCH !!!!!! ) the problem that I don’t have info about the IP of the Cisco switch the D.g of the machine are not the switch IP please advice if someone have idea how to find the IP of the Cisco switch by command manipulation or maybe by sniffer that can by installed on the Linux machine?

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Use a console cable, 9600/8/n/1 plugged into the Cisco switch and review the configuration.

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I dont have access to the cisco SWITCH !!!!!! – Diana Aug 18 '11 at 14:07
So you're saying you have no physical access to it? – SpacemanSpiff Aug 18 '11 at 14:22
yes I dont have physical access and I dont have sys network admin – Diana Aug 18 '11 at 16:26
I agree with Ryan, just ask someone, or start a sniffer and see if you can listen for broadcasts from any device that you don't know about. – SpacemanSpiff Aug 18 '11 at 16:28

I'd use nmap or angryIP scanner to see if the switch has an IP on the network.

Since it's a Cisco switch, just get a console cable & log into the switch.

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I dont have access to the switch , please explain about nmap or angryIP scanner - how to use / download – Diana Aug 18 '11 at 13:58
go to and download the proper version. Then put in your IP range which looks like it would be to and hit start – tkrabec Aug 18 '11 at 14:06
this is my recommendation also. it should work. – Sirex Aug 18 '11 at 14:29
unless it doesn't have an IP address in the subnet he searches... it might even be worth your time to check your ARP table and see if it's in there: arp -a. Of course, you always have the possibility that the switch is an unmanaged layer 2 switch that doesn't have an IP address. – Safado Aug 18 '11 at 14:47

Ask the Network Admin that manages the switch what the IP address is. You said you don't have physical access to it which I'm guessing means it's managed by someone else. Ask that someone else.

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funny - I dont have physical access and I dont have sys network admin – Diana Aug 18 '11 at 16:26
Well then I would hope you're not trying to gain access to a switch that doesn't belong to you... anyway, just open a command prompt on your Linux box and type "nmap -P0" With "??" being the CIDR notation of your subnet mask – Safado Aug 18 '11 at 16:54

Your question is not very clear. If you need the IP address of the switch in order to update its configuration, I recommend you just connect a console cable.

The most direct answer to your question is that you can use CDP to discover details about the directly connected device if no one has disabled CDP on it. You'll need to install this software to do this:

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I dont have access to the cisco SWITCH !!!!!! – Diana Aug 18 '11 at 13:59
Then running a CDP client on your linux server is the best option to try to get this information. Though, it is far from obvious why you would need the switch's IP address. – JakePaulus Aug 18 '11 at 14:23
please explain what the add value of the CDP client – Diana Aug 18 '11 at 16:28
By default, cisco network devices advertise information about themselves using the Cisco Discovery Protocol. This information includes software version, connected interface, model number, features supported, and the IP address of the device. Some folks like to disable CDP for security reasons, but, if it's running, it will tell you what you want to know. – JakePaulus Aug 18 '11 at 16:38

One possible method, if the switch has CDP enabled, is to run wireshark or tcpdump on a port connected to the switch for 5-10 minutes. The CDP packets are pretty distinctive and usually contain a management address for the switch.

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If you use tcpdump, you can use a command like this tcpdump -nn -v -i eth0 -s 1500 -c 1 'ether[20:2] == 0x2000' – c4f4t0r Oct 18 '13 at 10:33

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