From owner-freebsd-questions Tue Dec 19 00:29:31 1995 Return-Path: owner-questions Received: (from root@localhost) by freefall.freebsd.org (8.7.3/8.7.3) id AAA00631 for questions-outgoing; Tue, 19 Dec 1995 00:29:31 -0800 (PST) Received: from widget.xmission.com (root@widget.xmission.com [198.60.22.228]) by freefall.freebsd.org (8.7.3/8.7.3) with SMTP id AAA00626 for ; Tue, 19 Dec 1995 00:29:27 -0800 (PST) Received: (from rlenk@localhost) by widget.xmission.com (8.6.12/8.6.12) id BAA01075 for questions@freebsd.org; Tue, 19 Dec 1995 01:29:18 -0700 From: Ron Lenk Message-Id: <199512190829.BAA01075@widget.xmission.com> Subject: Shared IP addresses... To: questions@freebsd.org Date: Tue, 19 Dec 1995 01:29:17 -0700 (MST) X-Mailer: ELM [version 2.4 PL24] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-questions@freebsd.org Precedence: bulk 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