I thought I was out of the woods with this one but I'm not. I was able to get the site-to-site tunnel up when I originate traffic from the 172.18.3.x/24 subnet going to the 172.22.3.x subnet but not the other way around.
I get this with debug crytpo isakmp sa on the 1720:
*Mar 1 04:21:03: ISAKMP (0:1): processing NOTIFY PROPOSAL_NOT_CHOSEN protocol 3
spi 0, message ID = -1652585053
*Mar 1 04:21:03: ISAKMP (0:1): deleting node -1652585053 error FALSE reason "informational (in) state 1"
*Mar 1 04:21:03: ISAKMP:received payload type 0
*Mar 1 04:21:03: %CRYPTO-6-IKMP_MODE_FAILURE: Processing of Informational mode failed with peer at 18.104.22.168
*Mar 1 04:21:03: ISAKMP (0:1): received packet from 22.214.171.124 (I) QM_IDLE
*Mar 1 04:21:03: ISAKMP (0:1): processing HASH payload. message ID = -1420595240
*Mar 1 04:21:03: ISAKMP (0:1): processing DELETE payload. message ID = -1420595240
*Mar 1 04:21:03: ISAKMP (0:1): deleting node -1420595240 error FALSE reason "ISAKMP Delete notify (in)"
*Mar 1 04:21:03: ISAKMP (0:1): deleting SA reason "P1 delete notify (in)" state(I) QM_IDLE (peer 126.96.36.199) input queue 0
*Mar 1 04:21:03: ISAKMP (0:1): deleting node -1553921438 error FALSE reason "P1 delete notify (in)"
When I ping from 172.18.3.1 to 172.22.3.1 the tunnel comes up fine. I can access the 172.18.3.x subnet at this point from the 172.22.3.x subnet and all the servers there. I just can't initiate the tunnel traffic from the 1720 side.
Configs and diagram attached.
I believe you still forgot to move the dynamic map on the ASA to the last position in the crypto map.
With the current config, inbound connections on the ASA always land on the dynamic map, which uses 3DES. The 1720 only offers DES, so the negotiation fails.
If you still have a problem after moving the dynamic map on the ASA, then please get the crypto debugs on both sides at the same time (deb cry isa, deb cry ips on the router; deb cry isa 10, deb cry ips 10 on the ASA) and post the entire output (e.g. if you still get PROPOSAL_NOT_CHOSEN then the part before that is interesting, as well as the corresponding part on the peer).