[strongSwan] IPTables NAT Query
Tormod Macleod
TMacleod at paywizard.com
Tue Apr 7 17:10:10 CEST 2015
Yeah, that was my mistake. I only need the second one.
I thought I needed the first one because IPTables Postrouting didn't
take place until after the kernel had determined whether the traffic was
to be tunneled but I was mistaken. I see now that Postrouting takes
place before the kernel determines whether or not the traffic is to be
tunneled.
Thanks for your help.
>>> Noel Kuntze <noel at familie-kuntze.de> 07/04/2015 12:37 >>>
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Hash: SHA256
Hello Tormod,
Okay. But still only one CHILD_SA is up and the other one not.
Mit freundlichen Grüßen/Kind Regards,
Noel Kuntze
GPG Key ID: 0x63EC6658
Fingerprint: 23CA BB60 2146 05E7 7278 6592 3839 298F 63EC 6658
Am 07.04.2015 um 13:35 schrieb Tormod Macleod:
> Hi Noel,
>
> I need the SNAT as the network on the right want to see the traffic
originate from the 1.1.1.0/24 range for internal routing purposes.
>
> I thought (Bryan Duff set me straight) I needed two Child SAs.
Because the right device is a Cisco device I had to configure two
separate Child SAs rather than do rightsubnet=c,d. It seems the Cisco
ASA wants to do it that way and it was causing me problems. Martin Willi
previously helped me with this (see attached).
>
> Cheers,
>
>
> Tormod
>
> >>> Noel Kuntze <noel at familie-kuntze.de> 06/04/2015 18:01 >>>
>
> Hello Tormod,
>
> There is a graph[1] that describes the path of the traffic in the
kernel.
>
> Why do you believe, that you have to apply SNAT/MASQUERADE?
> By the way, your tunnel setup is wrong.
> You define two IPsec tunnels, but there is only one being used:
>
> >SecurityAssociation-2{2}: INSTALLED, TUNNEL, ESP in UDP SPIs:
cb5e661f_i 9add0a95_o
> >SecurityAssociation-2{2}: AES_CBC_128/HMAC_SHA1_96, 0 bytes_i, 0
bytes_o, rekeying in 48 minutes
> >SecurityAssociation-2{2}: 1.1.1.0/24 === 192.168.0.0/16
>
> You should look for the reason that causes CHILD_SA of
"SecurityAssociation-1" to not come up.
> Also, with IKEv2, you can combine the subnets of all SAs into one.
>
> So you can build something like this:
>
> leftsubnet=a,b
> rightsubnet=c,d
>
> Mit freundlichen Grüßen/Kind Regards,
> Noel Kuntze
>
> GPG Key ID: 0x63EC6658
> Fingerprint: 23CA BB60 2146 05E7 7278 6592 3839 298F 63EC 6658
>
> Am 06.04.2015 um 16:36 schrieb Tormod Macleod:
> > Hello,
>
> > I'm currently testing a site to site VPN. I need to change both the
source and destination address on the left device before forwarding the
packets over the VPN to the right device. I believe it all happens in
the order below but I may be wrong.
>
> > 1 IPTables Prerouting
> > 2 Route selected
> > 3 A determination is made on whether the packets should be
encapsulated with IPSec
> > 4 IPTables Postrouting
> > 5 Packets are encapsultaed with IPSec where applicable
> > 6 Packets are forwarded
>
> > I believe I have a solution but I'm not sure whether it's the best
and I'd welcome some ideas...
>
> > In order to have the traffic encapsulated I had to create two child
SAs on the left side. The first has the original source address and the
translated destination address. This is only used in step 3. In step 4
the destination address is translated and by the time it gets to step 5
the traffic source and destination addresses match that of the second
child SA which also matches the single child SA on the right side.
>
> > I'm concerned that I might run into some problems with this
approach that I have not yet foreseen.
>
> > Here's my config...
>
> > config setup
> > # strictcrlpolicy=yes
> > # uniqueids=no
>
> > conn %default
> > ikelifetime=1440m
> > keylife=60m
> > margintime=3m
> > keyingtries=5
> > keyexchange=ikev2
> > authby=secret
> > left=10.180.0.12
> > leftid=2.2.2.2
> > auto=start
> > ike=aes128-md5-modp1536
> > esp=aes128-sha1
> > reauth=no
> > dpdaction=hold
> > dpddelay=40
>
> > conn SecurityAssociation-1
> > leftsubnet=10.176.0.0/13
> > right=3.3.3.3
> > rightsubnet=192.168.0.0/16
> > rightid=3.3.3.3
>
> > conn SecurityAssociation-2
> > leftsubnet=1.1.1.0/24
> > right=3.3.3.3
> > rightsubnet=192.168.0.0/16
> > rightid=3.3.3.3
>
>
> > Here's the statusall...
>
> > [root at localhost ~]# /opt/strongswan522/sbin/ipsec statusall
> > Status of IKE charon daemon (strongSwan 5.2.2, Linux
2.6.32-504.12.2.el6.x86_64, x86_64):
> > uptime: 3 days, since Apr 03 14:47:09 2015
> > malloc: sbrk 270336, mmap 0, used 210768, free 59568
> > worker threads: 11 of 16 idle, 5/0/0/0 working, job queue:
0/0/0/0, scheduled: 4
> > loaded plugins: charon aes des rc2 sha1 sha2 md5 random nonce
x509 revocation constraints pubkey pkcs1 pkcs7 pkcs8 pkcs12 pgp dnskey
sshkey pem fips-prf gmp xcbc cmac hmac attr kernel-netlink resolve
socket-default stroke updown xauth-generic unity
> > Listening IP addresses:
> > 10.180.0.12
> > Connections:
> > SecurityAssociation-1: 10.180.0.12...3.3.3.3 IKEv2, dpddelay=40s
> > SecurityAssociation-1: local: [2.2.2.2] uses pre-shared key
authentication
> > SecurityAssociation-1: remote: [3.3.3.3] uses pre-shared key
authentication
> > SecurityAssociation-1: child: 10.176.0.0/13 === 192.168.0.0/16
TUNNEL, dpdaction=hold
> > SecurityAssociation-2: child: 1.1.1.0/24 === 192.168.0.0/16
TUNNEL, dpdaction=hold
> > Security Associations (1 up, 0 connecting):
> > SecurityAssociation-1[4]: ESTABLISHED 41 minutes ago,
10.180.0.12[2.2.2.2]...3.3.3.3[3.3.3.3]
> > SecurityAssociation-1[4]: IKEv2 SPIs: 75498cd903d39dfa_i*
9dca56ab7071039a_r, rekeying in 23 hours
> > SecurityAssociation-1[4]: IKE proposal:
AES_CBC_128/HMAC_MD5_96/PRF_HMAC_SHA1/MODP_1536
> > SecurityAssociation-2{2}: INSTALLED, TUNNEL, ESP in UDP SPIs:
cb5e661f_i 9add0a95_o
> > SecurityAssociation-2{2}: AES_CBC_128/HMAC_SHA1_96, 0 bytes_i, 0
bytes_o, rekeying in 48 minutes
> > SecurityAssociation-2{2}: 1.1.1.0/24 === 192.168.0.0/16
> > And here's the IPTABLES commands I used to send traffic both
ways...
>
> > iptables -t nat -A PREROUTING -p tcp -s 10.176.0.10/32 -d
10.180.0.12/32 --dport 61001 -j DNAT --to-destination 192.168.1.1:23
> > iptables -t nat -A POSTROUTING -s 10.176.0.10/32 -d
192.168.1.1/32 -j SNAT --to-source 1.1.1.2
> > iptables -t nat -A PREROUTING -p tcp -s 192.168.1.1/32 -d
1.1.1.3/32 --dport 61002 -j DNAT --to-destination 10.176.0.10:23
> > iptables -t nat -A POSTROUTING -s 192.168.1.1/32 -d
10.176.0.10/32 -j SNAT --to-source 10.180.0.12
> > It's a bit convoluted but it works. I'd love to know if someone has
a better idea.
>
> > Cheers,
>
>
> > Tormod
>
> > Please consider the environment before printing this email
> >
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