IP Conflict/Duplicate

Unanswered Question
Jun 1st, 2010

Hi Guys,

Any suggestion on how to prevent, detect and contained IP conflicts/duplicats in Cisco switch network? Let us say I want to protect specific IP from assigning it to other host on the same vlan, is it possible?

Thanks in advance!

regards,

Gagamboy

I have this problem too.
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Ganesh Hariharan Tue, 06/01/2010 - 10:30

Hi Guys,

Any suggestion on how to prevent, detect and contained IP conflicts/duplicats in Cisco switch network? Let us say I want to protect specific IP from assigning it to other host on the same vlan, is it possible?

Thanks in advance!

regards,

Gagamboy

Hi Gagamboy,

If you want to bind a specific mac with ip address you can try with DHCP binding with static mac in switch that particular mac will be assigned with specific ip address,check out the below config for the same.

ip dhcp pool Server_Imp

host 10.10.10.11 255.255.255.0

client-identifier 0100.4563.d64b.4b

Hope to Help !!

Ganesh.H

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Leo Laohoo Tue, 06/01/2010 - 14:50

Ganesh's post is one way.  Another way is to reserve a segment of the subnet.  Say you have 192.168.99.0/24 and you say that the DHCP is only allowed to dish out IP addresses from the range of 192.168.99.101 to 192.168.99.250.  Cisco router/switches can support this too as well as other DHCP servers (UNIX, Linux, Windows, etc.).

gagamboy15 Tue, 06/01/2010 - 18:59

Thanks for the feedback guys.

But what I would like to do is, I don't want users to use/assign to their PCs the 192.168.1.1 - it is not included in DHCP pool (192.168.1.100-192.168.1.250)

Is it possible? can I bind the mac-address on it?

regards,

Gagamboy

Ganesh Hariharan Tue, 06/01/2010 - 22:03

Thanks for the feedback guys.

But what I would like to do is, I don't want users to use/assign to their PCs the 192.168.1.1 - it is not included in DHCP pool (192.168.1.100-192.168.1.250)

Is it possible? can I bind the mac-address on it?

regards,

Gagamboy

Hi Gagamboy,

You can configure ip exclude ip address under dhcp pool, in order that users should not use that ip address then you need to deploy security policy in desktop that users dont have privillage to change the ip address and dhcp configured on desktop.

Hope to Help !!

Ganesh.H

Remember to rate the helpful post

abersven Sun, 06/13/2010 - 10:40

Duplicate IP addresses should not be a problem even if you have hosts with statically configured IP addresses within the scope of the DHCP server.

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Any DHCP server should check if the IP address is available and not used before offering it to a host. This is done by pinging the IP address. If there is no answer the DHCP server proceeds and offer the IP address to the client.

By default, the IOS DHCP Server pings the address twice before assigning a particular address to a requesting client.

Normally this is enough but if you want to increase this you can use the following command:

Command

Purpose

Router(config)#   ip dhcp ping packets number

Specifies the   number of ping packets the DHCP Server sends to a pool address before   assigning the address to a requesting client. The default is two packets.   Setting the count argument to a value of 0 turns off DHCP Server ping   operation completely.

/André

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