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strange IP question



Hi,

I'm running into a continuous problem with a box that has several IP
numbers on an Ethernet interface. The problem persisted across the last
three releases of OpenBSD at least (currently: 3.6-stable), and is as
follows:

# /sbin/ifconfig fxp3
fxp3: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1400
        address: 00:30:48:51:58:55
        media: Ethernet autoselect (100baseTX full-duplex)
        status: active
        inet 172.16.60.1 netmask 0xffff0000 broadcast 172.16.255.255
        inet6 fe80::230:48ff:fe51:5855%fxp3 prefixlen 64 scopeid 0x4
        inet 180.180.60.10 netmask 0xffff0000 broadcast 180.180.255.255
        inet 10.200.0.81 netmask 0xfffffff8 broadcast 10.200.0.87

The 180.180 can be safely ignored - it's an artefact that's bound to go
away soon.

The packet filter allows 172.something and 180.180 to communicate, and
the 10.something to communicate with other 10.somthings.

Now, on pflog0, I see this:


11:25:35.937147 10.200.0.81 > 172.16.20.4: icmp: 172.19.100.7 unreachable - need to frag (mtu 1378)
11:25:41.536690 10.200.0.81 > 172.16.20.4: icmp: 172.19.100.7 unreachable - need to frag (mtu 1378)


Why does the (OpenBSD) router use 10.200.0.81 instead of 172.16.60.1 for
it's sender address, and how can i force it to use the 172.16.60.1 when
talking to the 172.16. network?

So far I assumed that it would talk to the 10.x peers using it's 10.x
address, and to 172.x peers using it's 172.x address, and so on.



Best,
--Toni++



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