[strongSwan] Question on selecting source address

[Tobias Brunner]

Hi,

> Kernel IP routing table
> Destination     Gateway         Genmask         Flags Metric Ref    Use
> Iface
> 10.2.0.0        *               255.255.0.0     U     1      0        0 eth1
> 10.6.0.0        *               255.255.0.0     U     1      0        0 eth0
> default         10.6.0.1        0.0.0.0         UG    0      0        0 eth0

You should use `ip route` to get a better picture of the installed
routes (e.g. the source IPs set for each route, and to see routes in
other routing tables).

> After query RTM_GETROUTE, it will collect all the possible route entries.
> 
> With above network setup it will collect two route entries to
> destination 10.2.1.xx.

Yes, the default route and with higher priority the more specific route
to 10.2.0.0/16.

> However only one entry will have src_host.

Which one?  That is not seen in the output of `route`, check with `ip
route`.

> Then when it loop through collected route entries to get the best source
> ip address, depends on the order of route entries

Yes, the first one tried is the 10.2.0.0/16 one.

>  it will hit the entry without source ip address but OIF first, that
> will break right away and give that address as best address, which is
> not what I wanted.

How so?  If the 10.2.0.0/16 route is used with eth1 assigned then the IP
on eth1 should get used, which is 10.2.1.170 on the client.  Isn't that
what you want?

Regards,
Tobias