The relay agent then retransmits the response on the local network. In this situation, the communication between the relay agent and the DHCP server typically uses both a source and destination UDP port of As described in RFC :Section 4.
DHCP clients are allocated leases that last for some period of time. Clients begin to attempt to renew their leases once half the lease interval has expired. If some other DHCP server is able to renew the lease, it will do so at this time.
In order for rebinding to work, when the client successfully contacts a backup DHCP server, that server must have accurate information about the client's binding. Maintaining accurate binding information between two servers is a complicated problem; if both servers are able to update the same lease database, there must be a mechanism to avoid conflicts between updates on the independent servers. When the lease expires, the client must stop using the IP address granted to it in its lease.
Since its lease has expired, it will accept any IP address offered to it. However, since its IP address has changed, any ongoing connections will be broken.
Reminder of the need for updating information
These attacks fall inter rao option web three main categories: Unauthorized DHCP servers providing false information to clients. The Relay Agent Information Option protocol extension RFCusually referred to in the industry by its actual number as Option 82   allows network operators to attach tags to DHCP messages as these messages arrive on the network operator's trusted network.
This tag is then used as an authorization token to control the client's access to network resources.
Because the client has no access to the network upstream of the relay agent, the lack of authentication does not prevent the DHCP server operator from relying on the authorization token. This fact, combined with the introduction of The challenges of key management and processing delays due to hash computation have been deemed too heavy a price to pay for the perceived benefits.