Date: Mon, 21 Aug 2000 20:25:25 -0700 From: "Larry Skarpness Jr." <larry@chainsoft.com> To: "Janko van Roosmalen" <janko@compuserve.com> Cc: <freebsd-questions@FreeBSD.ORG> Subject: Re: ARP issues with 2 or more multi-homed interfaces on same physical LAN Message-ID: <004a01c00be8$9cdc5ee0$0a00a8c0@chainsoft.com> References: <Pine.BSF.4.10.10008220246190.2305-100000@parmenides.utp.net>
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Janko,
Thanks for the quick response. Allow me to clarify the situation. The NICs
have different IPs, different networks, and differenct ethernet addresses.
They just happen to be connected to the same network hub. Obviously this is
a somewhat unusual configuration. The OS detects this situation as it
should, however it spews warning messages constantly when just one would be
enough.
Some might be asking why would you want to do this in the first place. I am
situtuated on a cable modem. The ISP has supplied two completely different
IPs and different networks through this one cable modem. The ISP severly
limits the upload bandwidth, even between IPs on networks within their
control. So I have also multi-homed these two machines to another private
local network on which other machines exist. NAT is also being used on one
of the public IPs to support other machines on the private network. All of
these machines and the cable modem are wired into the same network hub, as
there is no reason to physically seperate them. Through this mechanism all
the machines can reach eachother on the private net, and get out to the
internet.
Machine 1 has
NICA HUB1
IPA NETA (cable modem1) supports NAT to outside
NICB HUB1
IPB NETB (local1)
Machine 2 has
NICC HUB1
IPC NETC (cable modem1)
IPD NETB
Machine 3 has
NICD HUB1
IPE NETB
Cable mdem 1 on HUB1
I think this is a valid configuration. Machine 1 complains that ARPs on
NICA are picked up on NICB, which in this situation would be expected. Is
there some reason why the FreeBSD OS must be so noisy about it? I WANT two
or more NICs in the same machine on the same physical network. The hack I
made to if_ether.c forces the OS quiet about it. Others are in the same
situation and would probably like this option without the neccessity to
hack.
Larry
----- Original Message -----
From: "Janko van Roosmalen" <janko@compuserve.com>
To: "Larry Skarpness Jr." <larry@chainsoft.com>
Cc: <freebsd-questions@FreeBSD.ORG>
Sent: Monday, August 21, 2000 7:58 PM
Subject: Re: ARP issues with 2 or more multi-homed interfaces on same
physical LAN
>
>
> On Mon, 21 Aug 2000, Larry Skarpness Jr. wrote:
> >
> > Sometimes it is necessary to place two or more network cards in the same
> > machine and have them wired to the same physical LAN. There could be
> > several reason's for doing this. After researching this problem it is
> > apparent that others have made the same explicit decision to do so.
This
> > causes frequent messages to appear in the console and log like...
> > /kernel: arp:192.168.0.20 is on dc0 but got reply from
00:e0:98:71:63:fd
> > on ed0
> >
>
> Normally a message like this usually means than 2 NIC's have the same IP
> number or respond to the same IP number.
> All NIC's should have a different IP number, even if they are in the same
> hosts. In the troubleshooting chapter of Craig Hunt's "TCP/IP Network
> Administration" a similar incident is handled and solved.
> The first 3 bytes of the MAC indicate the manufacturer of the card
> "00:e0:98". You can download the "Ethernet vendor list" from www.ieee.org
> (oui.txt IIRC).
>
> Janko
>
>
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