I replaced the Cache RaQ 2 with another i386 box with fxp0 and ex0
which was used as a NAT box before.

fxp0 at pci1 dev 8 function 0: i82559S Ethernet, rev 9
fxp0: interrupting at ioapic0 pin 19 (irq 9)
fxp0: Ethernet address 00:30:05:0c:cf:82
inphy0 at fxp0 phy 1: i82555 10/100 media interface, rev. 4
inphy0: 10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, auto
ex0 at pci1 dev 9 function 0: 3Com 3c905-TX 10/100 Ethernet (rev. 0x0)
ex0: interrupting at ioapic0 pin 18 (irq 10)
ex0: MAC address 00:10:4b:26:69:7b
nsphy0 at ex0 phy 24: DP83840 10/100 media interface, rev. 1
nsphy0: 10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, auto

Then, the problem[1] was solved.

Though I wonder why my cobalt has such a problem, NetBSD/i386 is
working well.

Thanks!

[1] http://mail-index.netbsd.org/port-cobalt/2006/12/08/0002.html
-- 
NAKAJI Hiroyuki