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Cisco Helper Address and DHCP

By daniel_monroe ·
I work with a network that has 6 logical subnets on one interface (E0). We just obtained the sixth in order to move everything on the other five into one flat address space to relieve router congestion. In a test move of the PDC/DHCP server, we lost DHCP services. It has been suggested that the helper address on the router needs to point to the new address of the server in order to forward on DHCP requests to the new subnet. It is my understanding, however, that the helper address is used for forwarding UDP broadcasts between physical interfaces. It is my belief, therefor, that because all our logical subnets are on one physical LAN on only the single router interface, that this is pointless. I would appriciate any help in better understanding this, especially if the address does indeed need set.

Thanks

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Cisco Helper Address and DHCP

by daniel_monroe In reply to Cisco Helper Address and ...

Point value changed by question poster.

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Cisco Helper Address and DHCP

by jason.myers In reply to Cisco Helper Address and ...

Helper address is used anytime you need to forward broadcast packets between to subnets. The subnets are keeping the DHCP request which is a broadcast from getting to the desired server. If you apply the IP HELPER-ADDRESS command and specify the server ip address, it will forward all request on the logical interface that you issue the command to the server correctly. Remember that broadcasts do not get routed/forwarded.

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Cisco Helper Address and DHCP

by daniel_monroe In reply to Cisco Helper Address and ...

Thanks for the response. Using your info, I was able to find related information on Cisco's site that refreshed my memory and provided me with the needed infomration:
http://www.cisco.com/univercd/cc/td/doc/cisintwk/ics/cs006.htm

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Cisco Helper Address and DHCP

by daniel_monroe In reply to Cisco Helper Address and ...

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