Re: understand the source address selection in case when reply is sent out via another interface

Martin, if you do not have a nat, it wont replace the source address.
you are getting the standard behaviour as far as I know.

regards,

2017-06-15 11:02 GMT-03:00 Martin T <[email protected]>:
> Hi,
>
> I have a server with two networks interfaces: eth0(IPv4 address
> 10.10.10.73) and eth1(IPv4 address 192.168.1.16). In addition, there
> is a following static route in this server "main" table:
>
> # ip route show 172.16.0.0/24
> 172.16.0.0/24 via 192.168.1.252 dev eth1   src 192.168.1.16
> #
>
> Now when I send an ICMP "echo request" message from 172.16.0.0/24
> network to IP address 10.10.10.73, then it is sent out via eth1
> interface because of this static route. According to "ip route get
> 172.16.0.0" the source IP should be 192.168.1.16. However, when I
> tcpdump ICMP traffic on eth1 interface, then I can see that source IP
> is actually 10.10.10.73. Why is that so? When I read the
> http://linux-ip.net/html/routing-saddr-selection.html, then it says
> that "kernel will use the src hint from the chosen route path" which
> in this case is 192.168.1.16. Or is the first rule that if it is a
> reply package, then source IP is always the one which initial package
> was addressed to?
>
>
> thanks,
> Martin
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