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Author Topic: Static ARP entry for Windows Network Load Balancing  (Read 9131 times)

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Offline pat2012

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Static ARP entry for Windows Network Load Balancing
« on: June 14, 2013, 07:13:47 PM »
Hi all.

We have a Windows SharePoint Cluster setup using Windows NLB. I understand that they (our Systems Management folks) have observed the application intermittently becomes inaccessible - it's random. They opened a case with Microsoft and their suggestion was to add a static ARP entry unto the default gateway. They sent some documentation on how it is done on Cis...cough!, equipment.

The NLB system generated the IP and MAC address to be added.  The thing is that when I checked the default gateway (an ERS 8600), the mapping already exists in the ARP table.  Doesn't this mean a static entry would be redundant?

I admit I'm not familiar with the Windows NLB Sharepoint Cluster business so I'm a bit confused by what Microsoft is asking for and why.

Also the documentation makes it sound like it shouldn't/wouldn't work without this entry, but it does.  It's only at random times does it loose connectivity.  I don't think it went down for the week.  This Sharepoint site has been in production for quite some time.

I hate random problems.

Any insight you guys may have I'll appreciate.

Here's a link to one of the articles provided my Microsoft:

http://inetpro.org/wiki/Configuring_Cisco_to_work_with_a_Windows_NLB_Cluster

Thanks.


Offline Paul L

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Re: Static ARP entry for Windows Network Load Balancing
« Reply #1 on: June 14, 2013, 09:16:11 PM »
Hi Pat.

where are the servers located within your campus LAN?  Can we assume with this setup you have servers in the same VLAN sharing a virtual IP address?

if that is the case you need to configure NLB within the VLAN 

config vlan <vid> ip nlb-unicast-mode enable

here are the caveats. In v3 you didn't need to configure it. but in v4 its mandatory.




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Offline Paul L

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Re: Static ARP entry for Windows Network Load Balancing
« Reply #2 on: June 14, 2013, 09:19:10 PM »
in version v5 and up you have more NLB options.

config vlan <vid> nlb-mode <disable/igmp-mcast/multicast/unicast>
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Offline pat2012

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Re: Static ARP entry for Windows Network Load Balancing
« Reply #3 on: June 17, 2013, 10:05:47 AM »
Hi Paul.

The servers in question are VMs hosted on an HP Blade Chassis.  The Chassis has 2 Cis... internal switches but these a just L2.  Their uplinks go to a 5500 stack (also L2).  All servers in this chassis are on the same subnet.  So, yes.  The servers in the cluster are on the same VLAN sharing a virtual IP address.

I just checked the "Configuration VLANs and Spanning Tree" document in the ERS 8600 collection and saw the command you were referring to.  However, in this case the NLB is running in multicast mode.

The strange thing is that in the current configuration it works - it's just that every now and then (once or twice per week) the NLB breaks and the Sys Admins tell me that to recover, they restart the NLB service.  One of them thinks Microsoft is grasping at straws.

Oh yeah.  The ERS 8600 in question is running Rel 3.7.3....

Offline Paul L

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Re: Static ARP entry for Windows Network Load Balancing
« Reply #4 on: June 17, 2013, 11:02:12 AM »
you are right. It will either work or it won't. 
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Offline Michael McNamara

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Re: Static ARP entry for Windows Network Load Balancing
« Reply #5 on: June 18, 2013, 03:13:09 PM »
Windows Network Load Balancing is a really ugly solution, highly inefficient and should be avoided at all possible costs.

You are essentially sending the data to both (or multiple) servers and then the servers are deciding who is going to reply to the request. In order to-do this you need to have the IP/MAC address resolve to 2 separate physical ports which in the early days caused a lot of problems for the network manufacturers. These days the problems are well documented and the vendors have added features to help "deal" with the ill behavior.

The workaround was occasionally to create a static ARP/FDB entry for all the servers.

http://downloads.avaya.com/css/P8/documents/100123894

If they are at all interested in true scaling or redundancy investigate a true load-balancing solution.

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Offline TankII

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Re: Static ARP entry for Windows Network Load Balancing
« Reply #6 on: June 18, 2013, 05:36:09 PM »
Or, try the Multicast version of NLB and use PIM to manage it.

TankII