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DHCP relay does not work in failover ASA 5500 Series

What is DHCP Relay?

DHCP is an acronym used for Dynamic Host Configuration Protocol. This protocol utilizes a relay structure to connect with the DHCP server. It serves as proxy that is utilized by the DHCP broadcast messages. These broadcast messages are important to be routed to different sectors in the subnet. For the configuration of DHCP relay, the address of the DHCP server is essential so messages or data can be relayed.

The purpose of having DHCP relay agent is to permit DHCP clients and servers be placed on numerous networks. It is not difficult to set up DHCP in a definite network segment. Messages in the DHCP network are IP broadcast and this means that all computers on the sector can respond. All it takes is a single scope on a single DHCP server.

DHCP messages flow easily on a single subnet on a network. However, things get a bit complex when there are many subnets on the network. The reason why things are complicated is that by default, DHCP broadcast messages do not cross router boundaries.

Core issue

This issue occurs when the Cisco Adaptive Security Appliance (ASA) does not forward the DHCP responses to the client.

The problem can occur in the presence of these Cisco bugs:

Resolution

To resolve this issue, check the version of the ASA software used. If it is 7.1(1) or a lower version, download and upgrade to the latest ASA software.

Cisco bugs CSCsd92296 and CSCse11384 have been resolved in ASA version 7.1.2.5.

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