Книга: Windows Server 2012 R2 Storage, Security, & Networking Pocket Consultant

Avoiding IP address conflicts

Avoiding IP address conflicts

IPv4 address conflicts are a common cause of problems with DHCP. No two computers on the network can have the same unicast IP address. If a computer is assigned the same unicast IPv4 address as another, one or both of the computers might become disconnected from the network. More specifically, the computer already using the IPv4 address can continue using the address and any other computer that tries to use that IPv4 address is blocked from using it.

To better detect and avoid potential conflicts, you can enable IPv4 address conflict detection by following these steps:

1. In the DHCP console, expand the node for the server with which you want to work, press and hold or right-click IPv4, and then tap or click Properties.

2. On the Advanced tab, set Conflict Detection Attempts to a value other than 0. The value you enter determines the number of times the DHCP server checks an IP address before leasing it to a client. The DHCP server checks IP addresses by sending a ping request over the network.

REAL WORLD A unicast IPv4 address is a standard IP address for class A, B, and C networks. When a DHCP client requests a lease, a DHCP server checks its pool of available addresses and assigns the client a lease on an available IPv4 address. By default, the server checks only the list of current leases to determine whether an address is available. It doesn’t actually query the network to determine whether an address is in use. Unfortunately, in a busy network environment, an administrator might have assigned this IPv4 address to another computer or an offline computer might have been brought online with a lease that it believes hasn’t expired, even though the DHCP server believes the lease has expired. Either way, you have an address conflict that will cause problems on the network. To reduce these types of conflicts, set the conflict detection to a value greater than 0.

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