From: Colin Barber (Colin.Barber@xxxxxxxxxxxxxx)
Date: Thu Aug 22 2002 - 10:31:11 GMT-3
Sun quad Ethernet cards seems to use the same mac address for all four ports
by default. Looking at the cam entries on the switch it does indeed create
multiple cam entries. Therefore both machines would get each others traffic
as well as their own.
This would affect performance on the devices but they would still work.
Normally the Ethernet cards look for packets addressed to it's own mac
address, others are discarded. However as the mac address matches the
traffic would have to be passed up to layer 3 only for the TCP/IP stack to
reject the packet as it has no record for the flow. This operation would be
done by generating an interrupt on the main CPU which is why performance
would be affected.
Colin
-----Original Message-----
From: Brian [mailto:signal@shreve.net]
Sent: 22 August 2002 14:03
To: msnyder@revolutioncomputer.com
Cc: ccielab@groupstudy.com
Subject: RE: Challenge Question
On Thu, 22 Aug 2002, Michael Snyder wrote:
> The two ip address with one mac address isn't a problem. You can go
> into the ip advanced settings on a w2k box, and setup as many addresses
> as you like. As long as the machine responds to the arp ip lookup, it
> works.
>
> Two of the same mac addresses on the same subnet would be a bad thing.
> Might work if you are using a hub instead of a switch, but both machines
> would get each others traffic.
Are you 100% convinced that a switch would not install 2 CAM entries and
just send data to both? As far as both machines receiving eachothers
traffic, do you believe this would create a problem where the function is
lost, or just slow performance.........think about how that traffic would
be handled.
Brian
> > -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Brian
> Sent: Thursday, August 22, 2002 6:34 AM
> To: ccielab@groupstudy.com
> Subject: Challenge Question
>
> I know this group likes these challenge questions, so I have one for you
>
> and hopefully it has not been put to this group recently.
>
> You have two hosts each with identical MAC addresses on an ethernet LAN.
> They also have identical IP addresses. Why or why not would this be a
> problem for the client communicating (assuming each of the dupe machines
>
> doesnt need to communicate with eachother only to other hosts on the LAN
> and through the gateway)?
>
> Ok, similar to above, same MAC addresses but different IP addresses.
> Why
> or why not would this create communications on the LAN or through the
> gateway?
>
> good luck!
>
> Brian
>
>
>
> -----------------------------------------------
> Brian Feeny, CCIE #8036 e: signal@shreve.net
> Network Engineer p: 318.222.2638x109
> ShreveNet Inc. f: 318.221.6612
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