Re: How does my computer work with an empty arp table?
On Dec 12, 2006, at 10:08 AM, Javier Henderson wrote: The ARP table only contains information about machines on the directly connected collision domain(s). Are you sure it's not the same broadcast domain? Yes. The term "collision domain" predates the wide deployment of switches, and switches have to treat ARPs in a special fashion: A computer on port A on a switch would be on a different collision domain than a computer on port B on the same switch, yet as long as they're on the same VLAN (ie, broadcast domain), both would have each other in their resepctive ARP tables if they were exchanging Ethernet traffic. ...in particular, ARPOP_REQUEST traffic will be propagated to every port on the switch which is configured to be a part of that VLAN, or, quite possibly, other ports including "trunk ports" or sometimes even ports configured on other VLANs. [1] Many switches will do this for all ethernet packets with an ether_dhost (ie, destination MAC) of all-ones. -- -Chuck [1]: And yes, Virginia, this has negatory implications if your security relies on VLANs to actually be completely hidden from each other. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: How does my computer work with an empty arp table?
On Dec 11, 2006, at 11:14 PM, Martin Alejandro Paredes Sanchez wrote: Yes, you are right, I forgot about PPP. Many thanks. Also, the ARP table only contain info of your subnet The ARP table only contains information about machines on the directly connected collision domain(s). It's entirely possible to run multiple IP subnets on the same hub or switch, and even ARP for machines outside the configured subnet on one machine even when no IP routing information is available for that other subnet... -- -Chuck ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: How does my computer work with an empty arp table?
El Lun 04 Dic 2006 08:42, [EMAIL PROTECTED] escribió: > On Mon, Dec 04, 2006 at 10:26:46AM -0500, Lowell Gilbert wrote: > > [EMAIL PROTECTED] writes: > > > 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 mtu 1500 > > > options=8 > > > inet6 fe80::202:44ff:fe92:1875%rl0 prefixlen 64 scopeid 0x1 > > > inet 192.168.1.2 netmask 0xff00 broadcast 192.168.1.255 > > > > Maybe you are connected to your service provider by PPP-over-Ethernet? > > In that case, the PPP link (which doesn't need ARP) is your next-hop > > to the Internet, rather than the modem on the Ethernet link. > > Yes, you are right, I forgot about PPP. Many thanks. Also, the ARP table only contain info of your subnet maps ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"
RE: How does my computer work with an empty arp table?
> -Original Message- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] > Sent: Monday, 4 December 2006 2:15 PM > To: freebsd-questions@freebsd.org > Subject: Re: How does my computer work with an empty arp table? > > > On Sun, Dec 03, 2006 at 02:53:44PM -0800, Atom Powers wrote: > > On 12/3/06, [EMAIL PROTECTED] <[EMAIL PROTECTED]> 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. > > How can I watch what is going on? > You can see what's going on by su'ing to root, and typeing: tcpdump -ni rl0 then try pinging, or sending your traffic. You will then see the ADSL modem reply (or the PPoE traffic etc). Cheers, Paul ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: How does my computer work with an empty arp table?
On Mon, 4 Dec 2006 08:14:44 +0200 [EMAIL PROTECTED] wrote: > On Sun, Dec 03, 2006 at 02:53:44PM -0800, Atom Powers wrote: > > On 12/3/06, [EMAIL PROTECTED] <[EMAIL PROTECTED]> 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 ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: How does my computer work with an empty arp table?
On Mon, Dec 04, 2006 at 10:26:46AM -0500, Lowell Gilbert wrote: > [EMAIL PROTECTED] writes: > > > 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 mtu 1500 > > options=8 > > inet6 fe80::202:44ff:fe92:1875%rl0 prefixlen 64 scopeid 0x1 > > inet 192.168.1.2 netmask 0xff00 broadcast 192.168.1.255 > > ether 00:02:44:92:18:75 > > media: Ethernet autoselect (100baseTX ) > > status: active > > lo0: flags=8049 mtu 16384 > > inet6 ::1 prefixlen 128 > > inet6 fe80::1%lo0 prefixlen 64 scopeid 0x2 > > inet 127.0.0.1 netmask 0xff00 > > ng0: flags=88d1 mtu 1492 > > inet6 fe80::202:44ff:fe92:1875%ng0 prefixlen 64 scopeid 0x3 > > inet 91.124.65.146 --> 195.5.5.161 netmask 0x > > Maybe you are connected to your service provider by PPP-over-Ethernet? > In that case, the PPP link (which doesn't need ARP) is your next-hop > to the Internet, rather than the modem on the Ethernet link. Yes, you are right, I forgot about PPP. Many thanks. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: How does my computer work with an empty arp table?
[EMAIL PROTECTED] writes: > 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 mtu 1500 > options=8 > inet6 fe80::202:44ff:fe92:1875%rl0 prefixlen 64 scopeid 0x1 > inet 192.168.1.2 netmask 0xff00 broadcast 192.168.1.255 > ether 00:02:44:92:18:75 > media: Ethernet autoselect (100baseTX ) > status: active > lo0: flags=8049 mtu 16384 > inet6 ::1 prefixlen 128 > inet6 fe80::1%lo0 prefixlen 64 scopeid 0x2 > inet 127.0.0.1 netmask 0xff00 > ng0: flags=88d1 mtu 1492 > inet6 fe80::202:44ff:fe92:1875%ng0 prefixlen 64 scopeid 0x3 > inet 91.124.65.146 --> 195.5.5.161 netmask 0x Maybe you are connected to your service provider by PPP-over-Ethernet? In that case, the PPP link (which doesn't need ARP) is your next-hop to the Internet, rather than the modem on the Ethernet link. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: How does my computer work with an empty arp table?
On Sun, Dec 03, 2006 at 02:53:44PM -0800, Atom Powers wrote: > On 12/3/06, [EMAIL PROTECTED] <[EMAIL PROTECTED]> 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. How can I watch what is going on? ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: How does my computer work with an empty arp table?
On 12/3/06, [EMAIL PROTECTED] <[EMAIL PROTECTED]> 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-- ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"
