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Subject: Re: Firewall/DMZ routing
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> 08:33:08.160246 arp who-has A.B.C.154 tell A.B.C.145

It looks to me as if your ISP does not know you've subnetd your
subnet.

If it knew, it should never try to do an arp for the subnet
A.B.C.152/29 but route the ICMP to A.B.C.146 and that's it.

So the router of your ISP genuinely beleive that A.B.C.154 belongs to
its Ethernet reachable network (which is not as you have the FW in
between).

Olivier