Microsoft Network Load Balancing - multicast mode, VIP not reachable

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Jan 30th, 2009
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Hi all,

I've run into the issue as described in however the work-around recommended does not work. I'm trying to configure it on a cat 6509 ios 12.2(18)sxf12a so add the "disable-snooping" to the "mac-address-table static" but still can't reach the VIP from anywhere outside its own subnet.

Any ideas? Thanks.

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dave.keith Fri, 01/30/2009 - 08:09
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Check your routers ARP table to see if it knows the MAC of the NLB VIP. You may need to add a static ARP entry to correlate the VIP to the multicast-MAC. Cisco devices do not accept a multicast MAC in reply to an ARP for a unicast IP. That may be why you can get to the VIP from within its subnet but not from outside. Good luck.


graham-lewis Fri, 01/30/2009 - 08:20
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Hi Dave,

Thanks for the reply. I've tried a static ARP & MAC_Address entry and also disabled IGRP snooping on the interfaces, e.g.

arp 03bf.0a11.3d6a arpa


mac-address-table static 03bf.0a11.3d6a vlan 61 interface g4/3 g4/4 disable-snooping

This is what what my ARP cache and MAC address tables look like:

cat6#sh ip arp

Protocol Address Age (min) Hardware Addr Type Interface

Internet - 0000.0c07.ac3d ARPA Vlan61

Internet - 0022.bebd.1400 ARPA Vlan61

Internet 0 001b.38c2.f4c0 ARPA GigabitEthernet4/5

Internet - 0022.bebd.1400 ARPA GigabitEthernet4/5

Internet - 03bf.ac11.3d6a ARPA

cat6#sh mac-add static

Legend: * - primary entry

age - seconds since last seen

n/a - not available

vlan mac address type learn age ports


* 61 0022.bebd.1400 static No - Router

* --- 0000.0000.aaaa static No - Switch

* 61 3333.0000.000d static Yes - Gi4/4,Gi4/5,Router,Switch


* 61 3333.0000.0001 static Yes - Switch,Stby-Switch

* 61 0000.0c07.ac3d static No - Router

* --- 0022.bebd.1400 static No - Router

* 61 03bf.0a11.3d6a static No - Gi4/4

* 61 3333.0000.0016 static Yes - Switch,Stby-Switch


dave.keith Fri, 01/30/2009 - 08:37
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Hmmmm ... it looks like the MAC was typo'd. In your initial static ARP entry command it is 03bf.0a11.3d6a , while in the sho arp it is 03bf.ac11.3d6a . Could that be the problem ?


graham-lewis Fri, 01/30/2009 - 09:21
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No one is from the "real" config and the other from my testbed - I changed the IP address from 172.x.x.x (hex ac) to 10.x.x.x (hex oa). The last four octets in the MS NLB multicast address represents the IP address of the VIP. Good spot though!


bbouchaiba Thu, 02/12/2009 - 07:34
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Hi Lewis,

Were you able to fix your issue, I'm in the same situation.

graham-lewis Thu, 02/12/2009 - 07:43
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Yes, the fix worked in the "real" network. It looks like the problem was that I couldn't fully replicate the server's multicast behaviour in test.

bbouchaiba Thu, 02/12/2009 - 14:44
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Thanks Lewis


My NLB is still not working, are you running windows 2003 or 2008 ?


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