Special Forums IP Networking How to route packets back to incoming interface? Post 302993373 by flyingwalrus on Thursday 9th of March 2017 08:46:03 AM
Originally Posted by jim mcnamara
I don't quite get what you are trying to do. Maybe you want TAP - bridge from eth1: to eth0: Which you not have now. In other words segregate and bridge on this server. Is this box in the DMZ?
Mmmh. Ok let me try to eplain it...

The server hast 1 NIC (eth0) and is connected to the internet. There are several daemons running on it (Apache, FTP, ...). Now from time to time a script running on the machine has to connect by openvpn to some other servers of which I know only the domain name not the ip addresses because they change they rotate ips due load balancing and also have alot of IP ranges.

Now when script opens up a openvpn link (tun0) to connect to a openvpn host, all traffic of my server is then routed over the tun0 gateway. Therefor if some client tries to reach the Apache daemon under it's common address, he get's no reponse, because the reponse packet are not sent back on the eth0 interface but the tun0 route. So no more connection to the daemons are possible anymore until the openvpn connection is closed.

What I want now, is that the server responds to any ip packet it gets, on the same interface it was received. When the vpn link is up, all outgoing packets of tcp/udp traffic which were initiated by the server itself have to be routed to tun0, all answers on incoming packets on eth0 have to be answered to eth0.

Does this make any sense to you? Smilie
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SHOREWALL-TUNNELS(5)						  [FIXME: manual]					      SHOREWALL-TUNNELS(5)

tunnels - Shorewall VPN definition file SYNOPSIS
/etc/shorewall/tunnels DESCRIPTION
The tunnels file is used to define rules for encapsulated (usually encrypted) traffic to pass between the Shorewall system and a remote gateway. Traffic flowing through the tunnel is handled using the normal zone/policy/rule mechanism. See http://www.shorewall.net/VPNBasics.html for details. The columns in the file are as follows. TYPE - {ipsec[:{noah|ah}]|ipsecnat|ipip|gre|l2tp|pptpclient|pptpserver|COMMENT|{openvpn|openvpnclient|openvpnserver}[:{tcp|udp}][:port]|generic:protocol[:port]} Types are as follows: 6to4 or 6in4 - 6to4 or 6in4 tunnel. The 6in4 synonym was added in 4.4.24. ipsec - IPv4 IPSEC ipsecnat - IPv4 IPSEC with NAT Traversal (UDP port 4500 encapsulation) ipip - IPv4 encapsulated in IPv4 (Protocol 4) gre - Generalized Routing Encapsulation (Protocol 47) l2tp - Layer 2 Tunneling Protocol (UDP port 1701) pptpclient - PPTP Client runs on the firewall pptpserver - PPTP Server runs on the firewall openvpn - OpenVPN in point-to-point mode openvpnclient - OpenVPN client runs on the firewall openvpnserver - OpenVPN server runs on the firewall generic - Other tunnel type If the type is ipsec, it may be followed by :ah to indicate that the Authentication Headers protocol (51) is used by the tunnel (the default is :noah which means that protocol 51 is not used). NAT traversal is only supported with ESP (protocol 50) so ipsecnat tunnels don't allow the ah option (ipsecnat:noah may be specified but is redundant). If type is openvpn, openvpnclient or openvpnserver it may optionally be followed by ":" and tcp or udp to specify the protocol to be used. If not specified, udp is assumed. If type is openvpn, openvpnclient or openvpnserver it may optionally be followed by ":" and the port number used by the tunnel. if no ":" and port number are included, then the default port of 1194 will be used. . Where both the protocol and port are specified, the protocol must be given first (e.g., openvpn:tcp:4444). If type is generic, it must be followed by ":" and a protocol name (from /etc/protocols) or a protocol number. If the protocol is tcp or udp (6 or 17), then it may optionally be followed by ":" and a port number. Comments may be attached to Netfilter rules generated from entries in this file through the use of COMMENT lines. These lines begin with the word COMMENT; the remainder of the line is treated as a comment which is attached to subsequent rules until another COMMENT line is found or until the end of the file is reached. To stop adding comments to rules, use a line with only the word COMMENT. ZONE - zone The zone of the physical interface through which tunnel traffic passes. This is normally your internet zone. GATEWAY(S) (gateway or gateways) - address-or-range [ , ... ] The IP address of the remote tunnel gateway. If the remote gateway has no fixed address (Road Warrior) then specify the gateway as May be specified as a network address and if your kernel and iptables include iprange match support then IP address ranges are also allowed. Beginning with Shorewall 4.5.3, a list of addresses or ranges may be given. Exclusion (shorewall-exclusion[1] (5) ) is not supported. GATEWAY ZONES (gateway_zone or gateway_zones) - [zone[,zone]...] Optional. If the gateway system specified in the third column is a standalone host then this column should contain a comma-separated list of the names of the zones that the host might be in. This column only applies to IPSEC tunnels where it enables ISAKMP traffic to flow through the tunnel to the remote gateway(s). EXAMPLE
Example 1: IPSec tunnel. The remote gateway is and the remote subnet is The tunnel does not use the AH protocol #TYPE ZONE GATEWAY ipsec:noah net Example 2: Road Warrior (LapTop that may connect from anywhere) where the "gw" zone is used to represent the remote LapTop #TYPE ZONE GATEWAY GATEWAY ZONES ipsec net gw Example 3: Host is a standalone system connected via an ipsec tunnel to the firewall system. The host is in zone gw. #TYPE ZONE GATEWAY GATEWAY ZONES ipsec net gw Example 4: Road Warriors that may belong to zones vpn1, vpn2 or vpn3. The FreeS/Wan _updown script will add the host to the appropriate zone using the shorewall add command on connect and will remove the host from the zone at disconnect time. #TYPE ZONE GATEWAY GATEWAY ZONES ipsec net vpn1,vpn2,vpn3 Example 5: You run the Linux PPTP client on your firewall and connect to server #TYPE ZONE GATEWAY GATEWAY ZONES pptpclient net Example 6: You run a PPTP server on your firewall. #TYPE ZONE GATEWAY GATEWAY ZONES pptpserver net Example 7: OPENVPN tunnel. The remote gateway is and openvpn uses port 7777. #TYPE ZONE GATEWAY GATEWAY ZONES openvpn:7777 net Example 8: You have a tunnel that is not one of the supported types. Your tunnel uses UDP port 4444. The other end of the tunnel is #TYPE ZONE GATEWAY GATEWAY ZONES generic:udp:4444 net FILES
/etc/shorewall/tunnels SEE ALSO
http://shorewall.net/configuration_file_basics.htm#Pairs shorewall(8), shorewall-accounting(5), shorewall-actions(5), shorewall-blacklist(5), shorewall-hosts(5), shorewall_interfaces(5), shorewall-ipsets(5), shorewall-maclist(5), shorewall-masq(5), shorewall-nat(5), shorewall-netmap(5), shorewall-params(5), shorewall-policy(5), shorewall-providers(5), shorewall-proxyarp(5), shorewall-rtrules(5), shorewall-routestopped(5), shorewall-rules(5), shorewall.conf(5), shorewall-secmarks(5), shorewall-tcclasses(5), shorewall-tcdevices(5), shorewall-tcrules(5), shorewall-tos(5), shorewall-zones(5) NOTES
1. shorewall-exclusion http://www.shorewall.net/manpages/shorewall-exclusion.html [FIXME: source] 06/28/2012 SHOREWALL-TUNNELS(5)

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