I found a lot of stuff in the archives similar to my problem,
but not exact. Briefly:

I have a three-legged firewall.
Internal IP (on fpx2) is 192.168.1.254
External IP is (on fxp0) 207.232.115.249
No IP on DMZ interface (fxp1)
fxp0 and fxp1 are bridged

Things work fine, but I get an excessive amount of
messages logged like the following:

/bsd: arplookup: unable to enter address for 207.232.115.242

207.232.115.242 is on the same hub as the fxp1
interface (in the DMZ).

I don't even understand how this box manages to communicate
with 207.232.115.242, given that can't create an arp entry mapping
the IP address to a MAC address, but in any case I would appreciate
any advice on how to elimate these messages.

Some info that may be helpful to start:

From "ifconfig -A":
fxp0: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1500
        address: 00:a0:c9:db:e8:41
        media: Ethernet autoselect (100baseTX)
        status: active
        inet 207.232.115.249 netmask 0xfffffff8 broadcast 207.232.115.255
        inet6 fe80::2a0:c9ff:fedb:e841%fxp0 prefixlen 64 scopeid 0x1
fxp1: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1500
        address: 00:a0:c9:db:db:3c
        media: Ethernet autoselect (100baseTX)
        status: active
        inet6 fe80::2a0:c9ff:fedb:db3c%fxp1 prefixlen 64 scopeid 0x2
fxp2: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        address: 00:a0:c9:ce:0d:91
        media: Ethernet autoselect (100baseTX)
        status: active
        inet 192.168.1.254 netmask 0xffffff00 broadcast 192.168.1.255
        inet6 fe80::2a0:c9ff:fece:d91%fxp2 prefixlen 64 scopeid 0x3

From "brconfig -a":
bridge0: flags=41<UP,RUNNING>
        Configuration:
                priority 32768 hellotime 2 fwddelay 15 maxage 20
        Interfaces:
                fxp1 flags=3<LEARNING,DISCOVER>
                        port 2 priority 128
                fxp0 flags=3<LEARNING,DISCOVER>
                        port 1 priority 128
        Addresses (max cache: 100, timeout: 240):
                00:e0:52:04:d0:a4 fxp0 1 flags=0<>
                00:10:7b:42:f9:27 fxp0 1 flags=0<>
                00:10:5a:e0:67:4b fxp1 0 flags=0<>
                00:a0:c9:5e:a8:29 fxp0 1 flags=0<>
                00:03:9f:1b:b8:2f fxp0 1 flags=0<>
                00:50:ba:8f:58:68 fxp1 1 flags=0<>
bridge1: flags=0<>
        Configuration:
                priority 32768 hellotime 2 fwddelay 15 maxage 20
        Interfaces:
        Addresses (max cache: 100, timeout: 240):

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