From owner-freebsd-net  Wed Apr 25 13:15: 4 2001
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Date: Wed, 25 Apr 2001 20:14:55 +0000
From: Gunther Schadow <gunther@aurora.regenstrief.org>
Organization: Regenstrief Institute for Health Care
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To: freebsd-net@freebsd.org, freebsd-small@freebsd.org,
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Subject: VPN tunnel with DHCP ...
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Hi,

about my SOHO router project, I came accross a tough problem, may
be I overlook that there is a solution already? The VPN gateway
at the small office / home office (SOHO) has an IPsec tunnel 
connecting it to its headquarter:

setkey -c  <<END
  spdadd ${sohonet} ${homenet} -P out ipsec
     esp/tunnel/${sohoip}-${homeip}/require;
  spdadd ${homenet} ${sohonet} -P in ipsec
     esp/tunnel/${homeip}-${sohoip}/require;
END

now, the problem is that the ${sohoip} is dynamically assigned 
with DHCP. How can the gateway at the headquarter know that 
${sohoip} address?

Options I can see are:

A DNS (provided that the SOHO endpoint has a reliable name assigned
  by the ISP ... doesn't work for intermittent/dialup lines.)

B an authenticated message from the SOHO endpoint to headquarter
  stating that the network ${sohonet} is reachable through the 
  tunnel with endpoint ${sohoip}.

Is there anything like B defined in IPsec / ISAKMP or something?

regards
-Gunther

-- 
Gunther Schadow, M.D., Ph.D.                    gschadow@regenstrief.org
Medical Information Scientist      Regenstrief Institute for Health Care
Adjunct Assistent Professor        Indiana University School of Medicine
tel:1(317)630-7960                         http://aurora.regenstrief.org

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