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dhcp request over an isdn line


i have the task to configure a router so, that it forwards a dhcp request over

a isdn line to a dhcp server.

is it enough to configure "ip helper-address" to the dhcp server and then make packets to this server as interessting traffic ?

if yes, i have trouble to understand because the router receives a broadcastpaket from the clien - does it know to forward this paket as a unicast over the isdn line ?

this mean the router first hast to make the unicast and THEN check this packet to the list of interesting packets - not the other order.

i have troubles that the router initiates the isdn line when it receives the dhcp broadcast from the client pc.

thanks for any answer


Re: dhcp request over an isdn line


I really doubt if the DHCP Broadcast wait until an ISDN is set up and then the IP Address is assigned from the DHCP Server, across a BRI Line.

Just curious, why can't you make the Router itself a DHCP Server, rather than spending money on ISDN Calls every time an IP Address is required or a Lease is renewd.

Kind Regards,

Wilson Samuel

Hall of Fame Super Gold

Re: dhcp request over an isdn line


There are several things that must be done for this to work. The first important thing, as you mention, is to configure ip helper-address on the LAN interface of the router on which DHCP requests will be received. It is also necessary that the DHCP traffic be interesting traffic. And it is necessary that there be routing logic (static routes or whatever) so that the router will know to forward over the ISDN to get to the server. And the server side must have configuration to return the DHCP traffic (correct interface configuration, interesting traffic, routing logic that will forward traffic to the remote router over the ISDN).

I do not believe that the issue about timing of the DHCP over ISDN is a serious issue. The original DHCP request may or may not be completed in a timely fashion. Depending on how much traffic is interesting the link may already be up when the DHCP request is made. And if the first request does time out, the PC should issue another request. And when the next request is received the ISDN should be up and the connection established. Though I do believe that he makes an interesting suggestion about configuring DHCP on the router instead of using the remote server.



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