Re: IP6 addresses in my routing table

Moe Trin <ibuprofin@xxxxxxxxxxxxxxxxxxxxxx> wrote:
On Sun, 21 Jan 2007, in the Usenet newsgroup comp.unix.bsd.openbsd.misc, in
article <R9qdnQtThsa-HC7YnZ2dnUVZ_vfinZ2d@xxxxxxxxxxx>, dave wrote:

I apologise for the top post. The 6-byte addresses are now showing up in
the routing table for my second computer. The routing table shown below
is for my second computer, not the computer connected directly to the
internet. Talk about creeping crud!

192.168.5.1 00:00:24:c3:4c:c3 UHLc 1 0 - nfe0
^^^^^^^^^^^^^^^^^

You mean that? This entry merely means that the kernel knows how to
reach this computer which has that MAC address on this interface.

[compton ~]$ etherwhois 00:00:24
00-00-24 (hex) CONNECT AS
000024 (base 16) CONNECT AS
HOERKAER 7-9
DK 2730 HERLEV
DENMARK
DENMARK
[compton ~]$

You need to know that on the local segment, traffic is routed using
MAC addresses because this is how Ethernet works. Ethernet knows nothing
about IP addresses - simply because IP is only one of over 180 network
protocols that can be carried in Ethernet frames. IPv6 is another
protocol - coded differently from IPv4. When your application wants to
send something, the kernel looks at the routing table to see if the IP
address is local - if it is, it looks up the MAC address, and sticks that
on the front of the Ethernet packet. If the packet is going off the local
network - say to www.yahoo.com or something, the kernel sticks the MAC
address of the gateway onto the Ethernet packet and sends it to that
gateway on this wire - even though the IP packet that is _within_ this
packet has the IP address of www.yahoo.com or whoever you are sending it
to.

Now THIS is interesting! How does the mac address for a computer in
Denmark get inserted into my routing table? And why is it associated
with the gateway from this computer to my other computer which has the
internet connection? What is the effect of this mac address in the
routing gateway field on traffic between my two computers?

For more on what's in an Ethernet frame see RFC0894 (which you can find
using a search engine) and ftp://ftp.iana.org/assignments/ethernet-numbers.
For what is an IP packet, see RFC0791. For TCP packets which are within an
IP packet, see RFC0793. For the ARP protocol, which is how a host on an
Ethernet network finds the MAC address if it has the IP address, see
RFC0826. There is an enormous list of MAC address to manufacturers -
that's where the 'etherwhois' program is looking - but it has just under
10,000 entries, totaling about 2.8 megabytes. It's not likely to be useful
to you.

Old guy

Thanks Very Much for pointing me at relevantt RFCs. I will read them.
.

Relevant Pages

  • Re: IP6 addresses in my routing table
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    (comp.unix.bsd.openbsd.misc)
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  • Re: ARP - IP but why?
    ... Resolution Protocol and it matches up network addresses with hardware ... If you have a static IP address on an Ethernet network, ... ever need to translate the IP address to a MAC address? ... It sends out an ARP packet asking "who's got 192.168.0.1?", and the router replies with its MAC address. ...
    (comp.os.linux.networking)
  • Re: IP6 addresses in my routing table
    ... is for my second computer, not the computer connected directly to the ... MAC addresses because this is how Ethernet works. ... on the front of the Ethernet packet. ...
    (comp.unix.bsd.openbsd.misc)
  • Re: How to detect my own MAC address from outside Internet (!) (NOT with ipconfig all)
    ... Back when I was working for a living, I maintained an ethernet ... plant wide ethernet without regard to the network protocol that it ... its own that sends the packet from that gateway to the next. ... traces of the original MAC address are lost at that point. ...
    (microsoft.public.windowsxp.network_web)