ip helper / dhcp / source address

Dear all, i just wanted to check what the source address of the IP
packet that is generated by a router configured with 'ip helper
A.B.C.D' on a local interface would be.

i need to know this as the router is connected via an IPSEC VPN
(crypto enabled on the dialer0 interface) to a central location on
which the DHCP server is connected, and i need to be sure that the
forwarded dhcp request will generate crytpo.

Thanks

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