Is it possible to use DHCP with options just to get optional information but not ask/get IP address (IP address got with IKE in IPSEC tunnel establishment)

Sorin Paun lspaun at
Wed Feb 18 10:27:34 UTC 2009

Hello world

I have a tough question here, I'm searching from any valuable information on

1/ A host has already IP conection (IP address IP1)

2/ The host establish a IPSec connection to a SeGW/VPN. As part of the
tunnel establishment it gets a new IP address IP2 (tunnel inner address) in
the IKE exchange (fields internal_ipv4_address)

3/ Now the host wants to discover the SIP servers (P-CSCF in 3GPP IMS). The
clever guys in 3GPP said that it can do it by using DHCP with option 120.

Question : Can the host DHCP just for the purpose of getting the SIP Server
address (with option 120) but don't interfere with its already allocated IP
address by another entity & method ?


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