Otdfbt

I've configured a 3G IP Gateway of mine to connect using IKE Phase 1 Aggressive Mode with PSK to my openswan installation running on Ubuntu server 12.04. I've configured openswan as follows:

/etc/ipsec.conf:

version 2.0
config setup
 nat_traversal=yes
 virtual_private=%v4:10.0.0.0/8,%v4:192.168.0.0/16,%v4:172.16.0.0/12
 oe=off
 protostack=netkey

conn net-to-net
 authby=secret
 left=192.168.0.11
 leftid=@left.paxcoda.com
 leftsubnet=10.1.0.0/16
 leftsourceip=10.1.0.1
 right=%any
 rightid=@right.paxcoda.com
 rightsubnet=192.168.127.0/24
 rightsourceip=192.168.127.254
 aggrmode=yes
 ike=aes128-md5;modp1536
 auto=add

/etc/ipsec.secrets:

@left.paxcoda.com @right.paxcoda.com: PSK "testpassword"

Note that both left and right are NAT'd, with dynamic public IP's. My left ISP gives my router a public IP, but my right ISP gives me a shared dynamic public IP and dynamic private IP. I have dynamic dns for the public ip on the left side. Here is what I see when I sniff the ISAKMP protocol:

21:17:31.228715 IP (tos 0x0, ttl 235, id 43639, offset 0, flags [none], proto UDP (17), length 437)
 74.198.87.93.49604 > 192.168.0.11.isakmp: [udp sum ok] isakmp 1.0 msgid 00000000 cookie da31a7896e2a1958->0000000000000000: phase 1 I agg:
 (sa: doi=ipsec situation=identity
 (p: #1 protoid=isakmp transform=1
 (t: #1 id=ike (type=enc value=aes)(type=keylen value=0080)(type=hash value=md5)(type=auth value=preshared)(type=group desc value=modp1536)(type=lifetype value=sec)(type=lifeduration len=4 value=00015180))))
 (ke: key len=192)
 (nonce: n len=16 data=(da31a7896e2a19582b33...0000001462b01880674b3739630ca7558cec8a89))
 (id: idtype=FQDN protoid=0 port=0 len=17 right.paxcoda.com)
 (vid: len=16)
 (vid: len=16)
 (vid: len=16)
 (vid: len=16)
21:17:31.236720 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 456)
 192.168.0.11.isakmp > 74.198.87.93.49604: [bad udp cksum 0x649c -> 0xcd2f!] isakmp 1.0 msgid 00000000 cookie da31a7896e2a1958->5b9776d4ea8b61b7: phase 1 R agg:
 (sa: doi=ipsec situation=identity
 (p: #1 protoid=isakmp transform=1
 (t: #1 id=ike (type=enc value=aes)(type=keylen value=0080)(type=hash value=md5)(type=auth value=preshared)(type=group desc value=modp1536)(type=lifetype value=sec)(type=lifeduration len=4 value=00015180))))
 (ke: key len=192)
 (nonce: n len=16 data=(32ccefcb793afb368975...000000144a131c81070358455c5728f20e95452f))
 (id: idtype=FQDN protoid=0 port=0 len=16 left.paxcoda.com)
 (hash: len=16)
 (vid: len=16)
 (pay20)
 (pay20)
 (vid: len=16)

However, my 3G Gateway (on the right) doesn't respond, and I don't know why. I think left's response is indeed getting through to my gateway, because in another question, I was trying to set up a similar scenario with Main Mode IKE, and in that case it looks as though at least one of the three 2-way main mode exchanges succeeded.

What other explanation for the failure is there?

(The 3G Gateway I'm using on the right is a Moxa G3150, by the way.)

Check Moxa OnCell's system logs - it might be unhappy with OpenSWAN's response and just abort the exchange without further notice. Tinkering with the CLI also might be worth the effort - most manufacturers allow for some kind of debugging / packet tracing through the CLI.

Also if possible try to check if the response packet leaves your @left NAT router on its public interface and the address is being re-written to the public IP to rule out a possible routing / packet filtering problem in your infrastructure.