[LARTC] local address routeable?

[Christian Stuellenberg <christian_stuellenberg@web.de>]

Hello all,

I've got a problem to set up a configuration that shoud allow to route
packets that come in over a certain interface(s) IF1 that then should
go out to another interface IF2 but are addressed to the local address
of interface IF3.  So only if packets for the address of interface IF3
come in over interface IF3 they should be locally accepted.

            +------+
+---IF2/IP2-| HOST |-IF1/IP1---...LAN
.           +------+
.              |
.           IF3/IP3
|              |
|              |
|              |
+-Internet--...+

So, to accomplish the above scenario, I thought that it must be
possible to change the routing tables in such a way, that also the
local interfaces become routeable (is this anyway possible?).

To do this, I wanted to remove the local IP3 from table local:
ip route del local $IP3 dev lo src $IP3 table local

Now I just put for test reasons the same entry to another table:
ip route add local $IP3 dev lo src $IP3 table $ANOTHER_TABLE
ip rule add from any lookup $ANOTHER_TABLE
ip route flush cache


To my thought, the routing up to now should not have changed its
behaviour, but the following occurs:  On the same host I could not
ping the IP3 any more and so also from any other host.

If I do a ip route get $IP3 the result looks like:
$IP3 via $DEFAULT_GW dev $DEFAULT_DEV src $DEFAULT_DEV_IP 
     cache  mtu 1500 advmss 1460

If I'm right, this should tell me, that the kernel now no longer can
recognize its IP3?!


So, is it possible to do what I wanted to do or did I did something
not the right way?


I'm sorry if this question has been asked over and over again, but I
have googled and looked into the archives but haven't found a solution
that fits my needs.

Best regards,
Christian

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