Date: Tue, 19 Dec 1995 01:29:17 -0700 (MST) From: Ron Lenk <rlenk@widget.xmission.com> To: questions@freebsd.org Subject: Shared IP addresses... Message-ID: <199512190829.BAA01075@widget.xmission.com>
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I will soon be using two FreeBSD boxes to route between two segments
of Ethernet, and after doing some thought about routing, and reading a
couple of books on the subject, I have come up with a rather
hypothetical question which I cannot answer.
The basic question that I have is whether it is a "correct" practice,
according to Internet standards, to use the same IP address on two
different network interfaces in the same machine. ( such as a point to
point link, and an Ethernet interface )
I have created two figures which help to better illustrate my
question. Assuming that routers 1 and 2 could be a FreeBSD machine,
or an actual router, and that the network between them could be either
a SLIP/PPP connection, or a leased connection, which of the two is the
more "correct" way of doing things?
It appears, to me, that the first figure is more "correct", assuming
that we actually have the three class C network numbers, because we
are not duplicating IP addresses on two different interfaces. This is
also the way that most of the larger network providers seem to do
things, usually with a netmask of 255.255.255.252 on the "middle"
network. Although, I have seen some smaller ISP which use the second
figure...possibly because they don't have excessive amounts of address
space to burn... :)
I would like to think that I have a fairly good understanding of
TCP/IP, but I can't seem to find a definitive answer to this
question...
Any insight would be helpful.
Ron
== Figure 1 ==============================================================
(Ethernet 1) 192.168.1.0
+----------------+---------------------------------------------------+
|
+----------------+-----------------+
| 192.168.1.1 (Ethernet interface) |
| (router 1) |
| 192.168.254.1 (Serial interface) |
+----------------+-----------------+
|
|
| (SLIP/PPP, Frame Relay, leased line, etc.) 192.168.254.0
|
|
+----------------+-----------------+
| 192.168.254.2 (Serial interface) |
| (router 2) |
| 192.168.2.1 (Ethernet interface) |
+----------------+-----------------+
|
+----------------+---------------------------------------------------+
(Ethernet 2) 192.168.2.0
== Figure 2 ===============================================================
(Ethernet 1) 192.168.1.0
+----------------+---------------------------------------------------+
|
+----------------+-----------------+
| 192.168.1.1 (Ethernet interface) |
| (router 1) |
| 192.168.1.1 (Serial interface) |
+----------------+-----------------+
|
|
| (SLIP/PPP, Frame Relay, leased line, etc.)
|
|
+----------------+-----------------+
| 192.168.2.1 (Serial interface) |
| (router 2) |
| 192.168.2.1 (Ethernet interface) |
+----------------+-----------------+
|
+----------------+---------------------------------------------------+
(Ethernet 2) 192.168.2.0
--
Ron Lenk -- rlenk@xmission.com
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