06-11-2019 12:52 AM
Let's say I have an IP for a workstation (e.g. 10.0.0.1) and IP for a Cisco router it's connected to (e.g. 10.0.0.254)
How can I find out the IP for the switch the workstation is connected to? What is the process? I want to find the specific switch and switchport to make changes
06-11-2019 01:07 AM - edited 06-11-2019 01:24 AM
Hello,
you know the end device IP 10.0.0.1 and you know the router IP 10.0.0.254.
a) connect to the router and use
show arp 10.0.0.1
You get the end user MAC address copy it to a text file
b) using show cdp neighbors detail
find out the directly connected switch to the router
Connect to the switch using telnet/SSH
Once inside the switch you can use the following command
show mac address-table address <end-user-address>
You put here the MAC address as seen on show ip arp command in format AAAA.BBBB.CCCC
at this point you find an interface :
or that interface is the access port to the end device and you have ended your search or it is a trunk port to another switch
in the second case you can use the show cdp neighbor detail to find out the management address of the switch.
and you repeat the whole procedure.
You connect to this swich via telnet/SSH and you issue
show mac address-table address <end-user-address>
Note:
on some switches you can use the command
traceroute mac <end-user-address> <end-user-address>
and this can tell you from the core switch the switch and the port to which the end device is connected.
However, this method does not work all the times.
Hope to help
Giuseppe
06-11-2019 01:22 AM
Hello,
what you need is the MAC address of your PC. Let's say that is 0050.7966.6800.
1. From the router, issue the command 'show arp 10.0.0.1':
R1#sh arp 10.0.0.1
Protocol Address Age (min) Hardware Addr Type Interface
Internet 10.0.0.1 1 0050.7966.6800 ARPA GigabitEthernet0/1
2. From the router, issue the command 'show cdp neighor detail' to find out which switch is connected to interface GigabitEthernet0/1:
R1#sh cdp neighbors detail
-------------------------
Device ID: Switch
Entry address(es):
Platform: Cisco , Capabilities: Router Switch IGMP
Interface: GigabitEthernet0/1, Port ID (outgoing port): GigabitEthernet0/1
Holdtime : 163 sec
3. From the switch, issue the command 'show mac address-table' this will show you which port on the switch the PC is connected to:
Switch#sh mac address-table
Mac Address Table
-------------------------------------------
Vlan Mac Address Type Ports
---- ----------- -------- -----
1 0050.7966.6800 DYNAMIC Gi0/0
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