How does my computer work with an empty arp table?

[a at zeos.net]

My computer is connected to ISP via ADSL and works properly.

I typed

arp -a

and saw an empty table, although I pinged successfully an Internet host
one second ago.

How does it work?

------------------------------------------------------------

$ ifconfig
rl0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
	options=8<VLAN_MTU>
	inet6 fe80::202:44ff:fe92:1875%rl0 prefixlen 64 scopeid 0x1 
	inet 192.168.1.2 netmask 0xffffff00 broadcast 192.168.1.255
	ether 00:02:44:92:18:75
	media: Ethernet autoselect (100baseTX <full-duplex>)
	status: active
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
	inet6 ::1 prefixlen 128 
	inet6 fe80::1%lo0 prefixlen 64 scopeid 0x2 
	inet 127.0.0.1 netmask 0xff000000 
ng0: flags=88d1<UP,POINTOPOINT,RUNNING,NOARP,SIMPLEX,MULTICAST> mtu 1492
	inet6 fe80::202:44ff:fe92:1875%ng0 prefixlen 64 scopeid 0x3 
	inet 91.124.65.146 --> 195.5.5.161 netmask 0xffffffff