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Networking Question

Posted on 2009-05-13
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Last Modified: 2012-05-06
Let's say you've got the following:
 
 1 blade server in a chassis. It's got two on board cisco switches in the
 chassis.
 
 The blade itself has two NIC's and one connects to one of the onboard
 switches and the other connects to the other onboard switch.
 
 Those two switches then connect up to a third switch.
 
 Lastly the two NIC's are teamed and each NIC is spoofed to have the same MAC.
 
 So, going out to the network, it seems pretty simple. I was just wondering
 how it's handled when data is being transmitted back to the blade server.
 
 For the third switch, does it have two entries in its table and they have
 identical MAC's at different ports? If that's the case, how does the
 switch decide to send to which port? Would it just randomly break the
 packet stream up or is there some other method? I know some switches need
 to be "made aware" of the teaming or is this mandatory all the time?

Also, would this result in duplicate packets being sent to the blade server?
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Question by:msheppard74
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blue-screen earned 500 total points
ID: 24375747
Only one MAC will appear on the switch.  The switch dynamically learns where the MAC addresses are based on the source MAC address of the incoming Ethernet frames.  Traffic will be sent back towards the switch that most recently sent a packet to the third switch.  

To restate:  If I am a switch and I have two ports A and B and I see traffic coming in from MAC X on port A, I will forward packets for X towards port A.  Once I see MAC X on port B, I will delete the entry facing A and start sending packets for mac X  to port B.  Functionally, it will be as if the device was physically moved to another network.

There is no danger of duplicate packets.

Switches that are aware of the teaming (when directly connected to the server) can spread the load over multiple links using Etherchannel (802.3ad)
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Author Comment

by:msheppard74
ID: 24376001
So switches that are able to be teaming aware must be directly connected to the server in question?
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by:blue-screen
blue-screen earned 500 total points
ID: 24376060
Depends on what your intended benefit is.  For redundancy, no.  For bandwidth aggregation, yes (unless your switches support multichassis etherchannel.)  I would need to understand more about what you are trying to accomplish.  

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