Draft:IP address conflict

Comment: If WP:HOWTO is fixed and a couple general references added, this material can be incorporated into the encyclopedia either as a new section in IP address or as a stand-alone article. ~KvnG 14:20, 12 March 2015 (UTC)

@Kvng: Thank you. I welcome your input.   — Jeff G. ツ (talk) 05:37, 13 March 2015 (UTC)

Comment: I'm afraid that this really is mostly a matter of "How to resolve IP address conflicts", and WP:NOTHOWTO point 1 specifically prohibits us from getting into the "how to" business.

I do wonder whether some mention of IP address conflicts could be made at IP address. If it were, "IP address conflict" could be created as a redirect to point there. j⚛e decker^talk 05:22, 3 June 2014 (UTC)

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Eastmain (talk • contribs) 19:49, 31 August 2014 (UTC)

I placed the lede into IP address#Conflict.   — Jeff G. ツ (talk) 03:22, 14 September 2015 (UTC)

An IP Address Conflict occurs when two devices on the same local physical or wireless network claim to have the same IP Address - that is, they conflict with each other. Since only one of the devices is supposed to be on the network at a time, the second one to arrive will generally stop the IP functionality of one or both of the devices. In many cases with modern Operating Systems, the Operating System will notify the user of one of the devices that there is an IP Address Conflict (displaying the symptom error message) and then either stop functioning on the network or function very badly on the network, and the user will then be stumped as to how to resolve the conflict, probably considering the situation an emergency. In some unfortunate cases, both devices will function very badly on the network. In severe cases in which one of the devices is the gateway, the network will be crippled. Since IP Addresses are assigned by multiple people and systems in multiple ways, any of them can be at fault. The following information should help the reader to resolve the conflict.

• The initial symptom. Write down exactly (or print or photograph the screen containing) the entire "IP Address Conflict" error message. Many users experiencing the initial symptom will ignore it, hoping that it will go away (exactly the wrong approach for this symptom). In some versions of Windows, the message itself will reveal the IP Address and one or both of the conflicting MAC Addresses. In later versions of Windows such as Windows 7 or Windows Server 2008 R2, the reader will be referred to the Event Log, where one should find (via the Event Viewer) Event ID 4198 or 4199 entitled "TCP/IP Network Interface Configuration", which should reveal more information.
• ADDRESS: The IP Address that is in conflict (if the device's lease cannot be renewed producing a different Address). ADDRESS can be determined from the device's control panel or from "ipconfig" or a local equivalent.
• IDENTITY1: The identity of the device reporting the conflict, in layman's terms. This is generally the reader's PC, tablet, phone, etc. Without it, a report is useless.
• MAC1: The MAC Address of the device reporting the conflict. This should be a sequence of 12 hexadecimal digits, which may be separated into six groups of two by dashes or other separators. MAC1 can be determined by using "ipconfig /all" or a local equivalent to display MAC1. If the output of that command scrolls off the screen, run it again while filtering it through more by appending "|more". MAC1 may also be displayed in the properties of a device's NIC in one's "Windows Control Panel" named "Network Connections", printed on the back of the device near the network cable jack, and/or printed on the device's network card.
• IDENTITY2: The identity of the other device, in layman's terms. This is generally somebody else's PC or printer. IDENTITY2 can be determined through an inventory of all of the Network Interface Controllers (NICs) in all of the devices on the network (especially those containing the brand of NIC identified by IEEE OUI and Company_id Assignments), or through using "ping -a " ADDRESS from a working Windows PC on the same network to try to determine the NetBIOS or NetBEUI machine name of IDENTITY2. Many NetBIOS and NetBEUI compatible devices will report a machine name even if they are not running Windows. Once IDENTITY2 is determined, one should be able to do one of the following: get IDENTITY2 to release and renew its DHCP IP Address (if Windows, "ipconfig /release" followed by "ipconfig /renew" at the Prompt); change IDENTITY2's Static IP Address to one outside the DHCP Range (make sure no one else is using the new address first); or make an exception for IDENTITY2's Static IP Address within or at one end of the DHCP Range (requires a change to the configuration of the DHCP Server).
• MAC2: The MAC Address of the other device. MAC2 can be determined by using "arp -a " ADDRESS from a working Windows PC or a local equivalent on the same network to display the ARP Cache for ADDRESS until one gets a response different from MAC1. One may have to ping ADDRESS in order to repopulate the ARP Cache.

An inventory of the the local network (containing IP Addresses, MAC or Physical Addresses, NETBIOS Machine Names, and device identification in layman's terms} can help to alleviate future frustration in case of another conflict. Tools that can help in this process from the Windows command line are "arp -a" and "ping" IP Address, as well as asking the DHCP Server what devices it's serving.

External links

• RFC 2131 - Dynamic Host Configuration Protocol
• RFC 2132 - DHCP Options and BOOTP Vendor Extensions
• RFC 3046 - DHCP Relay Agent Information Option
• RFC 3942 - Reclassifying Dynamic Host Configuration Protocol Version Four (DHCPv4) Options
• RFC 4242 - Information Refresh Time Option for Dynamic Host Configuration Protocol for IPv6
• RFC 4361 - Node-specific Client Identifiers for Dynamic Host Configuration Protocol Version Four (DHCPv4)
• RFC 4436 - Detecting Network Attachment in IPv4 (DNAv4)
• Article ID: 133490 - Last Review: October 15, 2013 - Revision: 5.0