10-04-2010 11:44 AM - edited 03-06-2019 01:18 PM
Hello,
How is it possible to detect/locate/discover a duplicate IP address in a network (LAN)?
I have recently found in one of my LAN (remote site) that a switch has the same address as the virtual VRRP (adress of my two WAN devices). I had often many connectivity issues because of this conflict but when i connect to WAN devices i ping the shared address without any problem, thus for me no problem with the adress.
- How can I know if the adress match the VRRP or the switch ?
- Does someone know some cisco advanced command to see this in cisco routers or switchs ?
- is the show mac-address-table can give me the two mac if any conflict occurs ? so i can locate the port.
- from my switch, is there any command to have all ip address of devices connected in LAN ? or mac-addresses ?
Many thanks for help.
Regards,
10-09-2010 11:25 AM
Hi,
- To see if it is the VRRP address I would say you should use the vrrp show command to see the IP and the MAC
VRRP Show |
---|
Router# show vrrp Ethernet0/1 - Group 1 State is Master Virtual IP address is 10.21.0.10 Virtual MAC address is 0000.5e00.0101 .............. |
- "show arp" will show you if you have 2 MAC's or more with the same IP
- To find the direction, you can search trough the network with "show mac add add aaaa-bbbb-cccc" and you will the the port, channel, etc..
"show ehterchannel summary" and "show cdp neigh gig" (For example)" helps to find the direction.
Hope that helps or give you some ideas.
best regards,
Sebastian
10-09-2010 12:09 PM
s.helmer wrote:
- "show arp" will show you if you have 2 MAC's or more with the same IP
Incorrect, since per standard there cannot be more than one MAC per IP, °show arp° will never show that.
10-09-2010 12:42 PM
your're right Paolo, Sorry.
Maybe a syslog entry could help.
10-09-2010 01:39 PM
Use the show arp command
example,
Example:-
Switch#show arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 10.1.1.1 - 00E0.F97A.7958 ARPA Vlan1
Internet 10.1.1.20 0 0001.64EE.6301 ARPA Vlan1
Note :- Red result is the duplicate address of two routers and "0" indicates duplicate address
OR
use "show cdp neighbors detail"
Example :-
Switch#show cdp neighbors detail
Device ID: Router
Entry address(es):
IP address : 10.1.1.20
Platform: cisco C1841, Capabilities: Router
Interface: FastEthernet0/1, Port ID (outgoing port): FastEthernet0/0
Holdtime: 148
Version :
Cisco IOS Software, 1841 Software (C1841-ADVIPSERVICESK9-M), Version 12.4(15)T1, RELEASE SOFTWARE (fc2)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2007 by Cisco Systems, Inc.
Compiled Wed 18-Jul-07 04:52 by pt_team
advertisement version: 2
Duplex: full
---------------------------
Device ID: Router
Entry address(es):
IP address : 10.1.1.20
Platform: cisco C1841, Capabilities: Router
Interface: FastEthernet0/2, Port ID (outgoing port): FastEthernet0/0
Holdtime: 128
Version :
Cisco IOS Software, 1841 Software (C1841-ADVIPSERVICESK9-M), Version 12.4(15)T1, RELEASE SOFTWARE (fc2)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2007 by Cisco Systems, Inc.
Compiled Wed 18-Jul-07 04:52 by pt_team
advertisement version: 2
Duplex: full
Switch#
10-09-2010 01:48 PM
Switch# show ip arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 10.1.1.1 - 00E0.F97A.7958 ARPA Vlan1
Internet 10.1.1.20 21 0001.64EE.6301 ARPA Vlan1
10-11-2010 07:48 AM
Hi reddy,
Thanks for your help.
Using the show arp or show ip arp in my router or my catalyst 2960, i see just 3 or 4 mac-address whereas i have many others workstations in the LAN.
is there any possibility or others command to have MAC or IPs addresses of all devices conencted to my LAN ?
Thanks again.
Regards,
AA
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