IPsec - got ESP going, but not AH

[Crist J. Clark]

On Fri, Apr 23, 2004 at 08:02:15AM -0400, Greg Troxel wrote:
> While this should probably work, it's more straightforward to use ESP
> with integrity protection.  That is, use a -A hmac-sha1 argument also
> to ESP.  (hmac-md5 is probably still fine, but sha1 goes better
> strength-wise with rijndael-cbc.)
> 
> I believe that in tunnel mode AH and ESP integrity are essentially
> identical - but read RFC2401 and rfc2401bis (i-d from ipsec wg) if you
> really want to understand.

Not true. ESP integrity does not cover the IP header, only the ESP
payload. Look at the diagrams in section 3.1 of RFC2406.

> In transport mode, AH protects parts of
> the original (and only) IP header.

Not true. AH protects the entire datagram, including payload. Again
hop down to section 3.1 of RFC2402 for that RFC-ASCII art we all love
so much.

As for the original problem. I've seen AH problems before. Follow the
"Single IP host and IPsec tunnel mode experience" thread from -hackers
from last year about this time.
-- 
Crist J. Clark                     |     cjclark at alum.mit.edu
                                   |     cjclark at jhu.edu
http://people.freebsd.org/~cjc/    |     cjc at freebsd.org