How does my computer work with an empty arp table?

[Jona Joachim]

On Mon, 4 Dec 2006 08:14:44 +0200
a at zeos.net wrote:

> On Sun, Dec 03, 2006 at 02:53:44PM -0800, Atom Powers wrote:
> > On 12/3/06, a at zeos.net <a at zeos.net> wrote:
> > >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.
> > 
> > The ARP table is a cache of known ARP<->IP addresses. If there are
> > no addresses in the ARP table then the system will send out an ARP
> > broadcast to discover the ARP address that belongs to the IP
> > address. Of course only the Ethernet hosts on your local network
> > will be in your ARP table.
> > 
> > -- 
> > --
> > Perfection is just a word I use occasionally with mustard.
> > --Atom Ray Powers--
> 
> Thank you for response.
> 
> But why there is no MAC address of my ADSL modem connected via
> Ethernet? Does my host send broadcast frames to communicate with
> modem everytime?
> 
> Furthermore, when I ping the modem, a proper entry appears in table:
> 
> ------------------------------------------------------------------------
> $arp -a
> 
> $ping -c 1 rt # It is my modem
> PING rt.my.domain (192.168.1.1): 56 data bytes
> 64 bytes from 192.168.1.1: icmp_seq=0 ttl=254 time=1.298 ms
> 
> --- rt.my.domain ping statistics ---
> 1 packets transmitted, 1 packets received, 0% packet loss
> round-trip min/avg/max/stddev = 1.298/1.298/1.298/0.000 ms
> 
> $arp -a
> rt.my.domain (192.168.1.1) at 00:13:49:61:f9:b2 on rl0 [ethernet]
> ------------------------------------------------------------------------
> 
> But no entry appears when I communicate trough the modem.

Perhaps your modem works as a transparent bridge.

Jona