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Full Discussion: Openvpn nat and iptables
Special Forums Cybersecurity Openvpn nat and iptables Post 302985097 by end on Friday 4th of November 2016 07:21:18 PM
Old 11-04-2016
Openvpn nat and iptables

good day good people

hi

first to tell that firewall and vpn is working as expected, but I notice something strange.

I have host system 11.11.11.11(local ip) firewall is blocking everything except port to vpn.
I have vpn on virtualized system 22.22.22.22 (CentOS both host and virtual). They are behind MikroTik router and then to my ISP router. This is a home setup I'm just experimenting.

PREROUTING 11.11.11.11:1194 to 22.22.22.22:1194 all other is blocked by iptables.
POSTROUTING 22.22.22.22 to 11.11.11.11

I noticed with Wireshark from host 11.11.11.11 that while I'm connected to vpn from another pc that 11.11.11.11 is connecting to ip addresses of websites I visit while in same time is connected to vpn. like:

11.11.11.11 XX.XX.XX public ip
11.11.11.11 tcp udp sites i visit

but 11.11.11.11 is unnecessarily making connections to website ip addresses. She cannot make the reqests because DNS and ports for that are blocked. So this is because postrouting command my best guess. Can this somehow be disabled? First this is a security issue, second its unnecessary.

Someone told me that this is because NAT setup. but I believe that this can be disabled somehow, I didn't find solution yet so maybe someone know how.

thanks


Moderator's Comments:
Mod Comment We had to correct a lot of spelling errors. Please put more effort into using proper english

Last edited by Scrutinizer; 11-05-2016 at 04:48 AM.. Reason: Spelling
 

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SECVPN(1)						      General Commands Manual							 SECVPN(1)

NAME
secvpn - Control the Secure Virtual Private Network SYNOPSIS
secvpn [-v][-n][-s][-r] start|stop|routedel|routeadd|test|status [Host] DESCRIPTION
Secvpn builds a virtual private network (vpn) as defined in /etc/network/secvpn.conf. The vpn uses encryption based on ssh security. Before secvpn can be used you have to create some prerequisites. See PREREQUISITES below. The following subcommands may be used with secvpn: start is used to start the vpn. Secvpn will add new ppp interfaces necessary to make the vpn work, but will not automatically add routes (see the routeadd option below). If the recursive option is set, secvpn will log into the passive hosts and run "secvpn -r start" on them too. stop is used to stop the vpn. routeadd is used to setup new routing entries based on secvpn.conf. Secvpn will first add the route active->passive, then tell the passive host to add the route back. The route in the passive host will be added according to the configuration file there (in the passive host), so if the configuration files differ, things will not work. routedel will delete the routing entries built with routeadd. test checks whether the ppp interface is used to reach O_CRYPT_IP. status same as test, but checks all vpns if no host is named (instead of only active vpns as 'test' does). OPTIONS
-v verbose output -n do nothing -s be silent -r work recursive PREREQUISITES
Before secvpn can be used you have to enable passwordless ssh access for user "secvpn" from the initiator secvpn pc to the target secvpn pc. Use authorized_ keys or RhostsRSAAuthentication with the .shosts file. Have a look to the ssh - manpages for more information. Before secvpn can be used you have to give root rights for specific commands to the user "secvpn". This can be done with the followin com- mand: echo "secvpn ALL=NOPASSWD: /usr/sbin/secvpn, /usr/sbin/pppd" >>/etc/sudoers Before secvpn can be used you have to edit /etc/secvon.conf. See secvpn.conf(4). EXAMPLES
There are 3 examples in /usr/share/doc/secvpn/examples: Example1: secvpn acts as router connection 2 subnets Example2: secvpn having one lan-card and connect 2 subnets Example3: secvpn having one lan-card and connect 11 subnets in a tree structure OTHER
To have real security it is necessary to secure each secvpn host and to have firewalls on each secvpn host allowing only selected IP- Adresses and Ports to pass through the VPN. AUTHOR
Bernd Schumacher, HP Consulting, HEWLETT-PACKARD GmbH, Bad Homburg, 2000-2005 COPYRIGHT
Copyright: Most recent version of the GPL. On Debian GNU/Linux systems, the complete text of the GNU General Public License can be found in "/usr/share/common-licenses/GPL". SEE ALSO
secvpn(1) secvpnmon(1) ssh(1) timeout(1) secvpn.conf(4) secvpn August 2000 SECVPN(1)
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