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Re: 2401bis issues (possible) resolution

At 01:38 PM 10/7/2003 -0400, Angelos D. Keromytis wrote:
In our weekly teleconference, we discussed the following items from the issues list:
68 VPNs with overlapping IP address ranges
We believe that these items are implementation-specific and/or not applicable
to implementations in general (this applies in particular to 50 and partially
to 68). We invite one last round of comments on these items --- if you feel
strongly, yell!

Hi Angelos and list,

As invited, I am yelling :-)

#68 (as I think you have acknowledged) consists of multiple parts, some of which are implementation issues but not all. Part of #68 involved a capability in the protocol:

         b. They MUST negotiate a VPN subscriber ID using IKE, as
         noted above, to enable forwarding of inbound IPsec
         traffic after crypto processing.

When a security Gateway is operating on behalf of multiple contexts (e.g. multiple subscribers, or multiple ppvpn-style overlay addressing contexts), it is essential that the initiator be able to convey to the responder which context is being addressed. In the absence of a capability to signal this in IKE, the only full-functioned alternative is for the SGs to maintain a separate IP address to use for each supported context. This can waste a lot of addresses, and it isn't even as good anyway because it requires coordinated configuration on both ends to understand which IP address in each SG corresponds to which context.

My conclusion: 2401bis should support the concept of multiple contexts supported in an IPsec device, and IKE should provide a means to convey the desired context in the initial exchange.

Thanks, Mark