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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
Old 03-09-2017
Quote:
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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Route classifier in tc(8)                                              Linux                                             Route classifier in tc(8)

NAME
route - route traffic control filter SYNOPSIS
tc filter ... route [ from REALM | fromif TAG ] [ to REALM ] [ classid CLASSID ] [ action ACTION_SPEC ] DESCRIPTION
Match packets based on routing table entries. This filter centers around the possibility to assign a realm to routing table entries. For any packet to be classified by this filter, a routing table lookup is performed and the returned realm is used to decide on whether the packet is a match or not. OPTIONS
action ACTION_SPEC Apply an action from the generic actions framework on matching packets. classid CLASSID Push matching packets into the class identified by CLASSID. from REALM fromif TAG Perform source route lookups. TAG is the name of an interface which must be present on the system at the time of tc invocation. to REALM Match if normal (i.e., destination) routing returns the given REALM. EXAMPLES
Consider the subnet 192.168.2.0/24 being attached to eth0: ip route add 192.168.2.0/24 dev eth0 realm 2 The following route filter will then match packets from that subnet: tc filter add ... route from 2 classid 1:2 and pass packets on to class 1:2. NOTES
Due to implementation details, realm values must be in a range from 0 to 255, inclusive. Alternatively, a verbose name defined in /etc/iproute2/rt_realms may be given instead. SEE ALSO
tc(8), ip-route(8) iproute2 21 Oct 2015 Route classifier in tc(8)
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