[Openswan Users] Firewall rules for openswan behind NAT

Fred Weston fred.weston at lpga.com
Wed Nov 13 10:44:26 UTC 2013

Hello All,

I'm using OpenSwan with AWS to link two private VPC networks in different regions.

I'm having trouble getting my firewall ACLs right.  Everything works if I permit all traffic to the OpenSwan boxes, however when I try to get more restrictive and permit only the necessary ports things stop working.

One side has all traffic permitted inbound for the time being and I'm making ACL changes trying to restrict traffic to certain ports/protocols on the other side.

Both endpoints are behind 1:1 NAT.  Everything is permitted outbound on both sides.

>From reading online, I understand that the following ports and protocols should be all I need:

UDP 500
UDP 4500
IP Protocol 50
IP Protocol 51

I tried the above and had no luck.  As soon as I change from permitting all inbound to permitting only the above list the tunnel comes down.

I also tried permitting tcp/1721 and tcp/1723 and IP Protocol 47.

I am using AWS 'security groups' to control filtering and according to the docs (and my observations) security groups are stateful, so I am not sure why this isn't working.

Can anyone offer any suggestions?


Fred Weston

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