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RE: wired mac address posted 07/11/2005
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We still haven't solved the problem. But we got some feedback from Microsoft about this Network Load Balancing service for servers. 

 NLB will create a bogus MAC address and assign that bogus MAC address to each adapter in the NLB array. NLB will assign each NLB adapter a different bogus MAC address based on the host ID of the array member and this address will appear in the Ethernet frame header.  For example, in the figure below the NLB array MAC address is 02-bf-ac-10-00-01. NLB in unicast mode will take the array MAC address and for each NLB array member adapter change the second octet so that it consists of the NLB member’s host ID. 

The problem is that our lay3  Nortel switch 8600 is not doing its job properly. When it reples the ARP request, it reples to the bogus MAC address instead of the NLB array MAC address, which is the virtual MAC address and works as source MAC address in the ARP request packet. The wired thing is that the server doesn't that reply packet with bogus Mac address is for itself.

Here's the simplefied diagram:

Nortel 8600 L3 switch -------2950 Switch ----NLB servers

We are going to upgrade our Notrel switch and turn on the feature to enalbe NLB support and see what will happen next.

Thanks for your suggestion.

 

 


cacca mucca <caccamucca@xxxxxxxxxxx> wrote:

I don't work on the server side, but it sounds like misconfiguration on the 
server.
Try changing the NIC out if you are able to do so. I don't know if hard 
coding the arp entry in the router for the IP address will solve your issue, 
you can alway give it a try.

Please do come back and let us, the group, know what you find.



>From: Helena Qiu 
>To: cacca mucca , ccielab@xxxxxxxxxxxxxx
>Subject: RE: wired mac address
>Date: Thu, 7 Jul 2005 12:04:46 -0400 (EDT)
>
>Hi, Cacca. Thanks.
>
>This server only has a NIC. But it is part of loadbalancer cluster. We 
>configured a secondary virtual IP address with virtual MAC address, but not 
>the one showed in the mac-address table. The server is running Windows 
>2000.
>
>What confuses me most is why the mac-address table shows different from 
>ARP?
>
>Please advise, Appreciate your help.
>
>cacca mucca wrote:
>Just a guess here, does your server have multiple NICs? Configured as some
>WEIRD or incorrect virtual setup? What kind of OS is the server running?
>
> >From: Helena Qiu
> >Reply-To: Helena Qiu
> >To: ccielab@xxxxxxxxxxxxxx
> >Subject: wired mac address
> >Date: Thu, 7 Jul 2005 00:41:10 -0400 (EDT)
> >
> >I connected a server to the port fa0/19 of 2900 switch. When I show
> >mac-address-table, it shows mac add 02:02:0A:D2:0C:A4 to this port. When 
>I
> >show arp, it shows the server IP has another MAC 02:BF:0A:XXXXXX, which 
>is
> >assigned as virtual MAC to the server's adapter. And I cannot find where
> >the MAC is assigned 02:02:0A:D2:0C:A4.
> >
> >The most wired thing is when I use span and sniffer the port in anothe
> >port, i find the server use 02:02:0A:D2:0C:A4 as source MAC to send ARP
> >request, but inside the ARP packet, it use MAC 02:BF:0A:XXXXXX as source
> >MAC. When the router reply the ARP request, it use 02:02:0A:D2:0C:A4 as
> >target MAC, and then it fails because the MAC add is not exist.
> >
> >When I sniffer in the server, i find that server sending ARP request with
> >MAC 02:BF:0A:XXXXXX as source. It's so wired.
> >
> >Please let me if you have any idea about this problem. And any special
> >meaning about the MAC 02:02:0A:D2:0C:A4, is it use for any special
> >application?
> >
> >Pls. advise. Thanks.
> >
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