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New Member

IP helper-address with IP address x.x.x.x y.y.y.y.y secondary

I have an ethernet interface on a branch router using the Secondary command. I want the clients on that logical network to have their DHCP discovery broadcasts forwarded accross that router to a remote DHCP server.

WIll forwarding broadcast work for the secondary network or will the router use its primary interface range to source the directed broadcast? What in the forwarded packet tells the DHCP server what pool to assign a client an address from?

3 REPLIES
New Member

Re: IP helper-address with IP address x.x.x.x y.y.y.y.y secondar

I have tried in the past to do the same thing and it is a no go. The client DHCP request are handled by the primary IP address and therefore sourced from that IP address to the DHCP server. The server never sees the secondary IP address of the router interface.

Unless there has been some new solution provided by cisco recently you will need to provide a different approach.

HTH

New Member

Re: IP helper-address with IP address x.x.x.x y.y.y.y.y secondar

There is a work around on the server, but it is not pretty. If the server is Windows NT or 2000, you can create a DHCP superscope. A superscope contains multiple scopes that exist on the same network (broadcast domain). So you can create a scope for the router's primary IP address (with no available IP addresses in it), then create another scope that you want your clients assigned from, then place both scopes into a single superscope. The DHCP server will then see DHCP packet relayed from the routers primary IP, and assign an IP address from any scope within the superscope.

Like I said, not pretty, but it will work.

hope this helps

tim

New Member

Re: IP helper-address with IP address x.x.x.x y.y.y.y.y secondar

Look at http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fipr_c/ipcprt1/1cfdhcp.htm#xtocid25. I haven't tried it out yet but I think the smart relay option could be at least a part of the solution for you.

Regards,

Mat

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