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Connecting L2 Switches to L3 Switch

Connecting L2 Switches to L3 Switch

swIn the topology above I have 6 Servers , each server has 2 Nics teamed up. each Nic is connected to a separate L2 Switch. The Back of Each L2 Switch, assuming it has only one Fastethernet which is connected as Trunk  to L3 Switch.
On L3 Switch there are 6 Vlans in addition to Vlan1. I have 6 SVI , each one will be configured as the Default Gateway of each server.

I posted this Diagram just to see if this is how Servers with teamed Nic can be connected to L2 and L3 Switches. There is redundancy at the Servers level as well as L2 Switches, but not at L3 Swicthes (It is Ok since It is not time yet to talk about FHRP)

I have attached a diagram file if you need to correct it and post back.


Thank you
Vmware-Cabling-Charts2.xlsx
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jskfan
Asked:
jskfan
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4 Solutions
 
atlas_shudderedSr. Network EngineerCommented:
If you connect the NICs to separate switches, you will run into a link flap scenario.  Connectivity to your servers will be dicey at best, if not having a significant negative impact to your network overall.  If you are trying to run HA redundancy, the best you could do in your scenario is connect both NICs to the same switch.  Next level up would be to connect each server to a stack of L2 switches.  From there, you will be looking at implementing hardware that can handle something like VPC, etc.

In other words, in your current environment you would connect server 1 to L2-1, server 2 to L2-2, server 3 to L2-1, etc.
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jskfanAuthor Commented:
if you connect each server (Both Nics) only to the same L2 Switch, then you will not have Redundancy. If L2 Switch goes down the server will be cut off the network.
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atlas_shudderedSr. Network EngineerCommented:
Correct, but by connecting to two different layer 2 switches, your links in the trunk are going to flab due to mac flapping, ergo, not only loss of HA but gross negative impact to your network at large.
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jskfanAuthor Commented:
so how do you guarantee HA ? is there any different design ?
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David Johnson, CD, MVPOwnerCommented:
There is a big difference between teaming the NIC's and connecting 2 NIC's to different switches.  When you team the nics they have a unique MAC/IP address so flapping won't occur.
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jskfanAuthor Commented:
So how do you create HA at the L2 switch level in this case ?
I believe you can Team up both Nics at the Server Level, and at the L2 switch level you can create an etherchannel. for both links to operate as one link.

But still there is no L2 Switch HA
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atlas_shudderedSr. Network EngineerCommented:
David, you can't team the NICs and connect to two different switches.  A team has one IP and one MAC.  The ports will flap.  This is not conjecture nor is it theory.  I've seen and corrected this exact scenario and its associated problems on more than one occasion.  You can potentially (depending on the equipment/OS) gain redundancy but lose bandwidth via active/passive teaming but active/active just will not work.
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jskfanAuthor Commented:
atlas_shuddered,

So how do you do it, when seeking High Availability ?
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atlas_shudderedSr. Network EngineerCommented:
If all you want is redundancy, you can connect the trunk active/passive (if your OS, etc. will permit) to the two different switches.  If you are looking for HA and bandwidth, you need to go active/active and connect either to one switch per server or use switch equipment that will allow you to bypass STP (using VSS/VPC/etc.).  If the thought of going to a single switch concerns or if the VSS/VPC capable equipment is not a budgetary option, you can also build your L2 switches into stacks of two switches and then drop one NIC from each server into switch one in the stack and the other into switch 2 of the same stack.  Alternate servers between stacks.  Alternate NICs between switches in a stack but don't alternate NICs between stacks.  Same principle applies as would with one server with a NIC in two different switches.
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jskfanAuthor Commented:
At this level, I guess
If all you want is redundancy, you can connect the trunk active/passive (if your OS, etc. will permit) to the two different switches.
 makes more sense.

So to confirm that I understand your comments, you cannot have 2 NIics of the server teamed up and connected to 2 separate L2 Switches.
However you can have one Nic Active, the other Nic in Standby and connect each Nic to a separate L2 switch ?
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atlas_shudderedSr. Network EngineerCommented:
Yes, if your OS will support the configuration.  Some don't, just a heads up.  What you will end up with is (assuming you are using gig NICs) is two one gig NICs configured into a one gig team with a failover path, no increase to available bandwidth.
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jskfanAuthor Commented:
Vmware ESX servers usually support one Nic Active the other Nic in standby.
Though I have seen 2 Nics teamed up, but I am not sure if they connect them to one switch or each Nic to separate Switch.
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David Johnson, CD, MVPOwnerCommented:
I know for a fact that with WS2016
To prevent the switches from getting confused and to prevent MAC flapping alarms, the source MAC address is replaced with a different MAC address on the frames transmitted on team members other than the primary team member. Because of this, each team member uses a different MAC address, and MAC address conflicts are prevented unless and until failure occurs.
https://docs.microsoft.com/en-us/windows-server/networking/technologies/nic-teaming/nic-teaming-mac-address-use-and-management
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JustInCaseCommented:
There are 2 different flavors of NIC teaming - switch dependent and switch independent.
Switch dependent methods is using 1 IP and 1 MAC address.
Switch independent will use 1 IP address and different MAC addresses for each network card (trying to protect server from situation where one of switches can fail).
Since MAC addresses are different for switch independent NIC teaming there will be no link flapping.
That would be the case - Route Based on Source MAC Hash (two VTEPs) -VM2 in the drawing (MAC B & D).
The above explanation may be oversimplification - I am not familiar with all possible approaches and configurations, but it should be good enough.

Both NICs on VMware host can be active at the same time (can be configured as active-standby or active-active)
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jskfanAuthor Commented:
Switch dependent methods is using 1 IP and 1 MAC address.

can this cause an issue, if the same MAC address is on both Switches ?
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atlas_shudderedSr. Network EngineerCommented:
jsk -

Yes, that is the active/active method I was talking about above.  It will lead to a MAC flap in your network with your trunk going up and down.

What Dave is referencing is the active/passive method.  You gain switch independence (HA) but lose any increase to bandwidth.
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JustInCaseCommented:
Switch independent mode does not necessary has to be connected to different switches.. so it can provide both higher throughput even when connected to one switch.
:)
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atlas_shudderedSr. Network EngineerCommented:
True Pre - but it defeats the attempt for HA, aside from port failure.
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jskfanAuthor Commented:
Since EE has changed the way to close the Questions. I can see  only the way to Select the Best Solution, but not how to Distribute the Points between Experts.

Any idea ?
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jskfanAuthor Commented:
Thank you Guys
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