Re: How to detect my own MAC address from outside Internet (!) (NOT with ipconfig all)
- From: John Wunderlich <jwunderlich@xxxxxxxxx>
- Date: Thu, 07 Feb 2008 20:57:21 GMT
"Jim" <j.n@xxxxxxxxxx> wrote in
news:Sxrqj.12844$EZ3.3933@xxxxxxxxxxxxxxxxxxxx:
That is most interesting information Chuck...
Back when I was working for a living, I maintained an ethernet
sniffer for VMS which ran DECnet. Regardless of that fact, my
sniffer detected every computer on our segment of the
plant wide ethernet without regard to the network protocol that it
was using. I understood at the time that all ethernet adapters
are expected to broadcast their address at
regular intervals. My program placed the ethernet adapter on our
VAX into promiscuous mode (which causes the adapter to pass all
packets to the software). A VAX had a hard time keeping up; when
I ported the program over to an Alpha, things worked much better.
I suppose my point is that a program can be written which grabs
all packets which pass by without regard to whatever structure the
IP believes it has. By the way, DECnet and IP can coexist on the
ethernet with no problems at all.
The MAC address exists at the lowest levels of the protocol stack and
is used as an outer wrapper to deliver a packet directly from one
device to another. If the destination device is a Router/Gateway, that
device then strips off the Ethernet wrapper and replaces it with one of
its own that sends the packet from that gateway to the next. All
traces of the original MAC address are lost at that point. A long time
ago, subnets were larger and broadcasts (like ARP) used to traverse
routers. Now, it is rare for a broadcast packet to survive past a
gateway.
Switches have now limited the amount of packets visible at an end
device to where promiscuous mode is almost moot. The only practical
way to find the MAC address of a device not on your subnet is to send a
packet to that device asking for it to reply with its MAC address.
That implies that a program or service is running on the target machine
that will willingly report that information. As part of the NetBT
service, Microsoft has provided that information by way of the
"nbtstat" program in which the target machine will report back its MAC
address among other info. Doing a remote registry query to the target
machine might be another way.
-- John
.
- References:
- Prev by Date: Re: Networking - Unable to ping self (XP Service Pack2)
- Next by Date: Re: network errors
- Previous by thread: Re: How to detect my own MAC address from outside Internet (!) (NOT with ipconfig all)
- Next by thread: Re: How to detect my own MAC address from outside Internet (!) (NOT with ipconfig all)
- Index(es):
Relevant Pages
|
