Hi, this is a somewhat hypothetical question about 2008 R2, but here goes... in situations where the NIC that can route the reply packet isn't the one that the packet arrived on, we know that the packet is dropped. Reading posts and blogs, I see that ip forwarding is suggested. That makes sense. I also see weak host suggested. That also makes sense. Some posts rather breezily suggest either as if they're the same (which they're not)! This http://workinghardinit.wordpress.com/2010/07/23/reflections-on-getting-windows-network-load-balancing-to-work-part-2/ intriguingly says that using weak hosts is "more atomic" but doesn't explain further. That got me thinking: in situations where either will work, which is best? Is there a best practice? Or, is one more scalable, future proofed, granular etc?

Hi, Thank you for the post. Both two methods work on NLB. I just see a blog to use ip forwarding not weak host, so I thought ip forwarding is the best. Compare their results, ip forwarding just open one way transfer (VNIC-->NIC) but weak host will cause two way transfer. http://blogs.technet.com/b/networking/archive/2008/11/20/balancing-act-dual-nic-configuration-with-windows-server-2008-nlb-clusters.aspx If there are more inquiries on this issue, please feel free to let us know. Regards, Rick Tan TechNet Subscriber Support If you are TechNet Subscription user and have any feedback on our support quality, please send your feedbackhere.Rick Tan TechNet Community Support

Hi Rick, thanks for the reply. Yes, both methods will work and I have read the article you referenced, but it just says to use ip forwarding with no explanation why. I'm sorry but I don't completely follow what you mean when you said that "ip forwarding just open one way, but weak host will cause two-way transfer" because both are set on a per-interface basis. Are do you mean that if I set weakhostsend on an interface, it automatically sets weakhostsend and weakhostreceive on all interfaces? (Which doesn't sound right to me.) Cheers

"when use weak host" - you are assuming that "weak host" is a per-host setting? However, it is per adapter. Also, weak host has two types: weak host send, and weak host receive. So, when you say "weak host send" is equivalent to: netsh interface ipv4 set interface "NLB NIC" forwarding=enabled netsh interface ipv4 set interface "Private NIC" forwarding=enabled exactly which weak host commands are you referring to?

Hi, In your posted article: http://workinghardinit.wordpress.com/2010/07/23/reflections-on-getting-windows-network-load-balancing-to-work-part-2/ Forwarding method command: netsh interface ipv4 set interface "NLB NIC" forwarding=enabled Weak host method command: netsh interface ipv4 set interface Private NIC weakhostsend=enabled netsh interface ipv4 set interface Private NIC weakhostreceive=enabled netsh interface ipv4 set interface NLB NIC weakhostsend=enabled netsh interface ipv4 set interface NLB NIC weakhostreceive=enabled So I stated weak host method equals to run command below and will cause the bidirectional forwarding. netsh interface ipv4 set interface "NLB NIC" forwarding=enabled netsh interface ipv4 set interface "Private NIC" forwarding=enabled RegardsRick Tan TechNet Community Support

Thank you. So I now know that running this: netsh interface ipv4 set interface Private NIC weakhostsend=enabled netsh interface ipv4 set interface Private NIC weakhostreceive=enabled netsh interface ipv4 set interface NLB NIC weakhostsend=enabled netsh interface ipv4 set interface NLB NIC weakhostreceive=enabled is the same as running this: netsh interface ipv4 set interface "NLB NIC" forwarding=enabled netsh interface ipv4 set interface "Private NIC" forwarding=enabled So, going back to the OP: what is the difference between the two? I find it hard to believe that the answer is "none at all" given that they are two different commands?

Hi Mark, I think these two commands are different with: If you enable the forwarding only, then the mode can possibly be the weak host mode but not the strong host mode. But if you enable the weak host mode only, then the mode can possibly be the weak host mode but not the strong host mode. Besides, "weak host mode" is the concept to "IP layer" while the "forwarding" is the concept to A"router". You can refer to the article: Source IP address selection on a Multi-Homed Windows Computer http://blogs.technet.com/b/networking/archive/2009/04/25/source-ip-address-selection-on-a-multi-homed-windows-computer.aspx Best Regards, Annie

Hi Mark, I think these two commands are different with: If you enable the forwarding only, then the mode can possibly be the weak host mode but not the strong host mode. But if you enable the weak host mode only, then the mode can possibly be the weak host mode but not the strong host mode. Besides, "weak host mode" is the concept to "IP layer" while the "forwarding" is the concept to A"router". You can refer to the article: Source IP address selection on a Multi-Homed Windows Computer http://blogs.technet.com/b/networking/archive/2009/04/25/source-ip-address-selection-on-a-multi-homed-windows-computer.aspx Best Regards, Annie

Hi Mark, I would like to confirm what is the current situation? If there is anything that I can do for you, please do not hesitate to let me know, and I will be happy to help. Regards, Rick Tan TechNet Subscriber Support If you are TechNet Subscription user and have any feedback on our support quality, please send your feedbackhere.Rick Tan TechNet Community Support

"If you enable the forwarding only, then the mode can possibly be the weak host mode but not the strong host mode. But if you enable the weak host mode only, then the mode can possibly be the weak host mode but not the strong host mode." They say the same thing - so does this mean that forwarding and weak host are actually the same? (I suspect that there is a typo there!) "Besides, "weak host mode" is the concept to "IP layer" while the "forwarding" is the concept to A"router". I get that weak host is an IP concept and forwarding is all about routing, but that really only explains it conceptually (as in "one is to do with routing but the other is to do with IP"). What I'm trying to get to the bottom of is: what in practice is the difference? I'm OK if someone says "actually there's no difference at all - two commands written by two different developers that were intended to be different but turned out to do exactly the same thing in practice". ;)

Hi Mark, Thanks for the post. I want to explain it further with the examples: If you have 2 NIC cards on the client :A=10.0.0.1, B=10.0.0.2. If you receive an IP address on this client point to the NIC B(10.0.0.2), but your A receive it. Then weak host mode will forward this package to the correct IP it defined. Of course, I think the IP forward= enable do the same thing as weak host mode since the destination IP is 10.0.0.2. However, if the client get another IP 10.0.1.10. IP forwarding will transfer this package to the correct network 10.0.1.x but weak host mode won't do that. I think this depends on the destination address: In my opinion, forward == from one network to another network host send ==from one nic to another nic Thanks. Annie

Hi Mark, Thanks for the post. I want to explain it further with the examples: If you have 2 NIC cards on the client :A=10.0.0.1, B=10.0.0.2. If you receive an IP address on this client point to the NIC B(10.0.0.2), but your A receive it. Then weak host mode will forward this package to the correct IP it defined. Of course, I think the IP forward= enable do the same thing as weak host mode since the destination IP is 10.0.0.2. However, if the client get another IP 10.0.1.10. IP forwarding will transfer this package to the correct network 10.0.1.x but weak host mode won't do that. I think this depends on the destination address: In my opinion, forward == from one network to another network host send ==from one nic to another nic Thanks. Annie