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    SubjectRe: Do Routing-policies have effect on local-originated packets?
    Andi Kleen wrote:
    >
    > adsmail@htl.de (Andreas Scherbaum) writes:
    > >
    > > Here's a tcpdump (sending a nameserver request to the second ip ...)
    > > $ host 192.168.0.1 192.168.0.201
    > >
    > > # tcpdump -p -i eth1:
    > > 18:13:59.988575 192.168.0.15.1128 > 192.168.0.201.domain: 34740+ (28)
    > > 18:14:00.036535 192.168.0.15.1128 > 192.168.0.201.domain: 34741+ (28)
    > >
    > > # tcpdump -p -i eth0:
    > > 18:14:09.514938 192.168.0.201.domain > 192.168.0.15.1128: 16413 1/3/3
    > > (161)
    > > 18:14:09.570556 192.168.0.201.domain > 192.168.0.15.1128: 16414 0/1/0
    > > (81)
    > >
    > > Why is the kernel sending this packages trough the first interface and
    > > how can i change it to using the right interface?
    >
    > Because the kernel does not know that the incoming packet and the outgoing
    > packet are in any way related (UDP has no connection between packets, it
    > is all in above layers if at all). The routing table doesn't say anything
    > about it. So the only way to get the semantics you want is to change bind
    > to receive the incoming interface with the IP_PKTINFO cmsg, look at the
    > ipi_ifindex and set it for outgoing packets on the same conversation to the
    > same interface.

    But why is this relevant for policy-routing? The kernel sees: the local
    packet has source-ip e.g. 192.168.0.2, then he looks at the rules...
    rules say sth like: "from 192.168.0.2 table 20", and table 20 says route
    through eth2
    or the source-ip is 192.168.0.3... rules say "from 192.168.0.3 table
    30", table 30 says route through eth3

    So where´s the difference between TCP and UDP here? am I missing sth?

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