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Use Echo Verification with Multiple DHCP Servers

Article Number: T003
Article Type: Tip
Modified: January 22, 1999

SUMMARY

If you have DHCP enabled on the Orbitor, and there is another server that also has DHCP enabled, you may want to consider using the ICMP Echo Verification feature of the Orbitor to prevent IP Address assignment conflicts.

MORE INFORMATION

When a client workstation/PC is configured to use DHCP to determine what IP address and other network configuration parameters it should use, it sends a DHCP request, encapsulated in an Ethernet broadcast to all stations on the local network. Those servers that are configured to respond to DHCP requests will see this broadcast and respond accordingly.

This in and of itself if just fine. In fact, it's the only way to provide DHCP server redundancy -- you must have more than one server configured to respond to DHCP requests in order to support DHCP server redundancy. The real issue occurs when there are overlapping IP address space assigned by each server. One server may allocate an IP address to a workstation, yet the other DHCP server may not be aware of this. As such, the second DHCP server may well allocate the same IP address without warning causing a conflict by the stations using the over-allocated address.

ICMP Echo Verification

Located on the DHCP setup menu of the Orbitor is a feature called ICMP Echo Verification. This feature will prevent the Orbitor from allocating an address already in use by another station.

By sending a PING (ICMP Echo Request) to the address it is about to allocate, it can detect if the address is in use by the response it receives for the PING. If response is not received for the PING, the Orbitor can be assured that the address is not currently in use and can safely be allocated.

CONSIDERATIONS

A similar feature may also be available on other servers. A check of their respective documentation will provide an answer to this question. If it is available, it should be enabled.

REFERENCES

Please consult the Orbitor Reference Manual for details regarding the use of these features.§

Copyright © 1999 Develcon Electronics Ltd.  All Rights Reserved.