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Re: Fw: Re: Block all servers?

  • From: Crist Clark
  • Date: Wed Oct 15 17:20:35 2003

Chris Brenton wrote:

> True this only works for one to one NAT. Many to one NAT will still
> break IPSec, even if ESP is used alone. This is a functionality issue
> however (IPSec using a fixed source port of 500), rather than a
> "preventing packet modification to thwart man-in-the-middle attacks"
> thing.

IPsec does not use port 500. IKE uses port 500/udp. IKE is an additional
protocol that is widely used to establish SAs and provide keying 
materials for IPsec, but it is not required for a compliant IPsec
implementation. In addition, most IKE implementations do not care
whether the source port on a IKE packet is 500/udp or not.

As I explained previously, ESP alone is un-NAT able in the general
case due to the fact that it is a peer-to-peer protocol, not client-to-
server, and the SPIs in either direction are unrelated.
Crist J. Clark                               [email protected]
Globalstar Communications                                (408) 933-4387