On Thu, 23 Apr 2020, John Serink wrote:

I'm on gentoo and I upgraded to 3.31 which broke all of my tunnels.
I'm connecting to a Cisco IOS and Digi Transport routers and the tunnels to the 
Cisco broke.
I'm sure the reason is this:

     ike=aes128-md5;modp1024
     phase2alg=aes128-md5;modp1024

Is there any way to "encourage" V3.31 to support the modp1024?

You have to recompile with with USE_DH2=true

Of course, it is strongly recommended you do not do this and fix those
tunnel configurations to not use crypto parameters from the 1990's.

See RFC 8247 https://tools.ietf.org/html/rfc8247

   Group 2 or the 1024-bit MODP Group has been downgraded from MUST- in
   RFC 4307 to SHOULD NOT.  It is known to be weak against sufficiently
   funded attackers using commercially available mass-computing
   resources, so its security margin is considered too narrow.  It is
   expected in the near future to be downgraded to MUST NOT.

Paul
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