How to know full network connectivity

[milanraheja1]

Hello everyone,

                          i am working with an ISP.here i am authorized to access all the switches of the network so by using #show cdp neighbour ... i can come wo know that how the switches are connected to each other and everything about switches i can see.but i want to know that how rest all the devices are connected with each other like how router , radius server and other devices are connected to each other.can anyone help to solve this please.......thanx.

Regards ,

Milan

[Philip D'Ath]

This is mostly an eyeball job.  Locate RADIUS server, follow patch lead to where it plugs into the switch.

Another method is to take the IP address of the device you want to locate (such as the RADIUS server), get it's MAC address (you can get this from the ARP table from a device in the same subnet after doing a ping), and then ask the switch where it is located.  For example:

ping 192.168.0.1

switch1#show arp | inc 192.168.0.1
Internet 192.168.0.1 0 0f50.56bd.47b8 ARPA Vlan1

switch1#show mac address-table | inc 0f50.56bd.47b8
 72 0f50.56bd.47b8 DYNAMIC Gi0/15

So now I know 192.168.0.1 is plugged into Gigabit0/15.  Note if this comes back as a trunk port going to another switch, you have to log into that other switch and repeat the process until you come back to an ordinary access port.

[Philip D'Ath]

ps. If you are doing a lot of devices, dump the ARP table from the core switch and put it into a spreadsheet. Them dump the mac forwarding tables all all the switches and also put them into a spreadsheet. Now what you do is search for the IP address of the device in the spreadsheet you want to find, and get it's MAC address, and then search for the MAC address and hey presto, you just found out what switch and port that device is plugged into.

[Philip D'Ath]

pps.  If you have quite new switches check out the "show ip device tracking" command.

http://www.cisco.com/c/en/us/support/docs/ip/address-resolution-protocol-arp/118630-technote-ipdt-00.html