ip forwarding and weak host difference?
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?
September 12th, 2012 4:00pm
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
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September 14th, 2012 3:50am
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
September 15th, 2012 5:55am
"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?
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September 17th, 2012 3:12am
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
September 17th, 2012 4:02am
Hi,
Are do you mean that if I set weakhostsend on an interface, it automatically sets weakhostsend and weakhostreceive on all interfaces?
No. I mean bidirectional forwarding when use weak host.
Weak host method equals to run command:
netsh interface ipv4 set interface "NLB NIC" forwarding=enabled
netsh interface ipv4 set interface "Private NIC" forwarding=enabled
Regards,
Rick Tan
TechNet Subscriber Support
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Rick Tan
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September 18th, 2012 12:50am
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?
September 18th, 2012 3:48am
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
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September 19th, 2012 4:32am