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naymar27
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vMAC address NSX

Hello guys,

I'm facing an issue with NetScaler in my infrastructure. My netscaler is connected to 2 DLR and I recently found in the logs that the two IP addresses of the DLR where having the same vMAC address:

192.168.200.254 02:50:56:56:44:52 0/1 1 DYNAMIC 1186 0

192.168.100.254 02:50:56:56:44:52 1/1 1 DYNAMIC 1162 0

I wish to know this is a bug? if, yes how can i solve it?

Thanks

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Sreec
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DLR has a VMAC concept and VMAC  is the vMAC that the DLR uses on all LIFs across all instances and MAC is the same on all hosts . If I'm not wrong your NetScaler is directly connected to DLR ?  You should also double check arp table of both the DLR and cross verify with the MAC what you are seeing 

nsxmgr# show logical-router host hostID dlr dlrID arp

Above command will show the ARP table and in the Expiry column you will see a permanent section which is nothing but a VMAC . So if the output is matching this is expected. 

If it doesn't match I would like to know the setup/configuration details of DLR interfaces along with a topology .

Cheers,
Sree | VCIX-5X| VCAP-5X| VExpert 7x|Cisco Certified Specialist
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Sreec
VMware Employee
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DLR has a VMAC concept and VMAC  is the vMAC that the DLR uses on all LIFs across all instances and MAC is the same on all hosts . If I'm not wrong your NetScaler is directly connected to DLR ?  You should also double check arp table of both the DLR and cross verify with the MAC what you are seeing 

nsxmgr# show logical-router host hostID dlr dlrID arp

Above command will show the ARP table and in the Expiry column you will see a permanent section which is nothing but a VMAC . So if the output is matching this is expected. 

If it doesn't match I would like to know the setup/configuration details of DLR interfaces along with a topology .

Cheers,
Sree | VCIX-5X| VCAP-5X| VExpert 7x|Cisco Certified Specialist
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naymar27
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The Netscaler is directly connected to the DLRs.

I checked that and the MAC address matches vMAC address:

192.168.200.254   02:50:56:56:44:52    VI         permanent  0          1          13880000000c

192.168.100.254   02:50:56:56:44:52    VI         permanent  0          1          13890000000a

Why is it using the vMAC address instead of the MAC address starting with 05?

Thanks Sreec

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Sreec
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This is by design and totally different comparing with general MAC creation of Virtual Machines in vSphere world. No matter how many DLR or NSX instances we have ,DLR VMAC remains the same . Considering the fact that we are using overlay networks, VMAC will never be learned by Switches (Only VM's will know/learn the same).  So in a nutshell overall ARP process will be like this

1.SRC MAC = vMAC, and DST MAC = Broadcast

2.SRC MAC = pMAC  and DST MAC = Broadcast (Now VTEP is involved and packet will be in encapsulated format)

3. When packet reaches the destination Host were we have the VM residing , SRC MAC = pMAC A, DST MAC = vMAC and sees its own LIF IP address requesting this. It saves the SRC MAC, and generates a new ARP Request packet, SRC MAC = vMAC, DST MAC = Broadcast

DLR ARP Resolution Process

Cheers,
Sree | VCIX-5X| VCAP-5X| VExpert 7x|Cisco Certified Specialist
Please KUDO helpful posts and mark the thread as solved if answered