Swapping MAC addresses?

John LLOYD jal at mdacorporation.com
Thu Sep 3 13:15:02 CDT 2009


For Windows boxen, just bond the NICs and use a single IP address.
Doing anything resembling ARP tuning on Windows is likely to be
troublesome.   

Bonding usually requires support from the switch (cisco LACP,
round-robin, etc etc etc).

Note that bonding on Windows (or linux for that matter) gives you
throughput increase and/or redundancy, depending on the details of the
bonding, but you don't get more than a single interface speed for any
one client.  It only helps serve multiple clients.   


--John



________________________________

	From: Chase Bolt [mailto:cbolt at datinggold.com] 
	Sent: Thursday, September 03, 2009 10:35 AM
	To: John LLOYD
	Cc: linux-poweredge at lists.us.dell.com
	Subject: Re: Swapping MAC addresses?
	
	
	On a similar note, does any one know how to do this arp tuning
on a Windows box? We only have about 4 windows boxes vs hundreds of
linux machines so it hasn't became a big issue, but I would like to have
this fix on them as well.
	
	
	John LLOYD wrote: 

			Date: Thu, 3 Sep 2009 09:14:17 -0700
			From: John Oliver <joliver at john-oliver.net>
<mailto:joliver at john-oliver.net> 
			Subject: Re: Swapping MAC addresses?
			To: linux-poweredge at lists.us.dell.com
			Message-ID:
<20090903161417.GA12153 at ns.sdsitehosting.net>
<mailto:20090903161417.GA12153 at ns.sdsitehosting.net> 
			Content-Type: text/plain; charset=us-ascii
			
			On Wed, Sep 02, 2009 at 05:18:48PM -0700, Chase
Bolt wrote:
			    

				I can't imagine he is rebooting once a
week, though if he 
				      

			was I would 
			    

				lean more towards Bryan on this.
				      

			I am not :-)  Current uptime is 35 days.  And
that reboot was 
			after this
			was reported...
			
			BTW, the config files *do* contain HWADDR lines.
			
			    

				Only time I have seen macs flipping like
this so often is 
				      

			when your have 
			    

				bonded your nics. Are you doing a load
balance or 
				      

			active/passive setup 
			    

				on your nics?
				      

			Nope.
			
			[joliver at mda-services ~]$ sudo cat
			/etc/sysconfig/network-scripts/ifcfg-eth0
			# Broadcom Corporation NetXtreme II BCM5708
Gigabit Ethernet
			DEVICE=eth0
			HWADDR=00:19:b9:ca:5b:44
			IPADDR=XXXXXXXXX.129
			    

		...snip...
		  

			[joliver at mda-services ~]$ sudo cat
			/etc/sysconfig/network-scripts/ifcfg-eth1
			# Broadcom Corporation NetXtreme II BCM5708
Gigabit Ethernet
			DEVICE=eth1
			HWADDR=00:19:B9:CA:5B:46
			IPADDR=XXXXXXXXX.47
			    

		
		There's your problem -- they are on the same subnet, no?
(your '129 IP
		and '47 IP have the same left-hand side).  You have two
NICs on the same
		subnet.
		
		You need to bond them, or disconnect one, or adjust some
ARP tuning,
		e.g. arp_filter=1 to force one or the other (only) to
respond to arp
		requests.
		
		(Think of it from the linux kernel point of view.  It
has a packet in
		hand, ready to go out to your subnet XXXXXXXX.  Which
interface should
		it use?  It has a choice of two, so, clearly, it is
changing it's mind
		from week to week....)
		
		
		--John
		
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